Are ABO Gene Alleles Responsible for Cardiovascular Diseases and Venous Thromboembolism and Do They Play a Role in COVID?

*Dennis J. Cordato, Wissam Soubra, Sameer Saleem and Kaneez Fatima Shad*

## **Abstract**

Cardiovascular diseases (CVD) including coronary heart disease and stroke are leading causes of death and disability globally. Studies of the association between ABO blood groups and CVD have consistently demonstrated an increased risk of coronary heart disease, myocardial infarction, cerebral ischaemic stroke, peripheral arterial disease and venous thromboembolism (VTE) including deep vein thrombosis and pulmonary thromboembolism in patients who possess a non-O blood group type. The most likely mechanism is thought to be the increase in von Willebrand Factor (vWF) and factor VIII levels seen in patients with a non-O blood group. Other postulated mechanisms include elevations in circulating inflammatory markers such as endothelial cell and platelet adhesion molecules in subjects with a non-O blood group. More recently, it has also been recognised that individuals with a non-O blood group type carry a higher risk of SARS-C0V-2 infection and COVID-19 related complications. The increased levels in vWF and factor VIII amongst individuals with a non-O blood group who have contracted SARS-CoV-2 infection may result in an additive thrombophilic effect to that caused by the SARS-CoV-2 virus. Another postulated mechanism is that individuals with an O-blood group are protected by anti-A and B antibodies which possibly inhibit the binding of the SARS-CoV-2 spike protein to lung epithelium angiotensin converting enzyme-2 receptors. There are over 35 minor blood groups on red blood cells, some of which such as Kidd, Lewis and Duffy have been associated with CVD either alone or in combination with a non-O blood group allele(s). However, their role in SARS-CoV-2 infection and mechanism of action for an association with CVD remain unknown. This review explores the relationship between ABO and minor blood groups with CVD and VTE, with a focus on potential mechanisms underlying this relationship and the potential role of ABO blood group types in COVID.

**Keywords:** cardiovascular diseases, venous thromboembolism, ABO blood group, von Willebrand Factor, COVID

## **1. Introduction**

Cardiovascular diseases (CVD) including coronary heart disease and stroke are the global leading cause of death and a major contributor to disability [1].

Traditional modifiable risk factors include hypertension, dyslipidaemia, diabetes mellitus, current smoking, obesity and physical inactivity and non-modifiable risk factors include age, gender, family history and ethnic background [2]. Amongst the non-modifiable risk factors, genetic variations in conjunction with traditional modifiable risk factors may significantly influence the trajectory of an individual's CVD risk [3]. Studies on the association between ABO blood group and CVD have consistently demonstrated that possession of the O blood group, the most common phenotype in most populations [4], confers protection against an individual developing a cardiovascular event [5–11]. The A and B blood groups are most frequently seen in Caucasian and Asian populations, respectively [4]. However, the magnitude of the association between CVD and ABO blood grouping across different ethnic populations is controversial in part due to the higher population attributable risk of traditional modifiable vascular risk factors [9, 10, 12].

There is also a well-documented interaction between ABO blood group and venous thromboembolism (VTE) [7, 13–15]. The A2 blood subgroup, which is less common than A1 and rare in Asian populations [5], has been reported to be associated with a modest VTE risk (Odds Ratio 1.2) whereas the A1 and B subgroups confer a 1.8-fold increased risk [7]. The non-O blood groups are associated with ~25–30% higher plasma levels of factor VIII and von Willebrand Factor (vWF) which are felt to be the major contributing factors to the increased risk of VTE [7, 16]. ABO blood grouping has been reported to influence activated protein C resistance [8], plasma lipid levels [11] and markers of inflammation including soluble intercellular adhesion molecule 1 (ICAM1), plasma soluble E-selection and P-selectin and tumour necrosis factor-alpha [11]. An additive effect on VTE risk and ABO blood group has also been described in association with factor V Leiden and prothrombin gene mutations [10, 17]. Finally, ABO blood grouping has more recently been reported to influence

#### **Figure 1.**

*ABO gene and their potential role in COVID-19, cerebral ischaemic disease, peripheral arterial disease, and myocardial infarction.*

*Are ABO Gene Alleles Responsible for Cardiovascular Diseases and Venous Thromboembolism… DOI: http://dx.doi.org/10.5772/intechopen.100479*

susceptibility to SARS-CoV-2 infection and an individual's propensity to more severe disease [18–20]. Proposed mechanisms include an additive risk of COVID-19 related thrombophilic complications in patients with a non-O blood group and a protective role of the O-blood group against the binding of the SARS-CoV-2 spike protein to lung epithelium angiotensin converting enzyme-2 receptor [18–20].

There are at least 35 minor blood group antigens in addition to ABO including Kidd, MNS, Duffy and Lewis [21] for which some, including Kidd and Lewis, have also been associated with CVD although the mechanisms of the associations are unclear [22–24].

This review will focus on the relationship between ABO blood types and CVD including coronary artery disease, ischaemic stroke, peripheral arterial disease and VTE (**Figure 1**). The contemporary relationship between SARS-CoV-2 infection, CVD and ABO blood grouping and the role of minor blood group antigens in the pathogenesis of CVD will also be discussed.

#### **2. The ABO blood group system**

The discovery of the ABO blood group system in 1900 by Austrian physician Karl Landsteiner saw him awarded of a Nobel Prize in physiology and medicine thirty years later [25]. The ABO blood group system consists of three main alleles A, B and O with codominant A and B alleles resulting in an inheritance pattern consisting of six genotypes and four major blood types [4, 25]. The ABO locus is found on chromosome 9 (9q34.1-q34.2) and codes for 2 glycosyltransferases A and B that transfer N-acetyl-D-galactosamine and D-galactose to a H antigen acceptor site on red blood cells (RBC) producing A and B surface antigens and blood group types, respectively (**Figure 2**) [26]. Lack of glycosyltransferase activity results in an unmodified ABO H antigen precursor and an O blood group type (O standing for 'Ohne', the German word for 'without') [25, 26]. Although ABO blood group antigens are RBC antigens, they are also expressed on human tissue including epithelial and endothelial cells [4].

The four basic ABO blood groups are O, A, B and AB. The ABO blood phenotypes have multiple subtypes, including A1, A2 and A3, in which 80% of blood group A cases are A1 in subtype, and O1, O2 and O3, in which O1 accounts for 95% of blood group O cases (**Table 1**) [4, 26]. From an evolutionary perspective, the oldest blood groups are A and O with A1 subtype considered the ancestral blood group [4, 7]. Single nucleotide polymorphisms (SNPs) of the ABO gene define the major haplotypes of European ancestry populations [7]. A substitution from proline to leucine at amino acid 156 results in a change from A1 to the less common A2 allele [5, 7]. Substitutions from glycine to serine at amino acid 235, leucine to methionine at amino acid 266 and glycine to alanine at amino acid 268 results in B allele subtypes [7, 27]. In contrast, the O1 type is a consequence of a frameshift deletion of guanine (cdel261G, p88fs118Stop) which translates to a protein without enzymatic activity [4, 5, 7].

There are significant geographic and racial variations in the distribution of blood groups across the world [4, 25]. Contributing factors include migration over the time of humankind's existence and processes of natural selection influenced by environmental factors such as climate and major diseases including malaria for which the O blood group confers protection [25]. Blood group A is predominant in Northern and Central Europe, B in Central Asia and O in Africa, South America, and Australia [4, 5, 25]. However, there are isolated populations within each continent that have a completely different blood group [4]. For example, the O blood group is common in different areas of Europe including Scandinavia and Switzerland [10, 25]. The most recent blood group, AB, appears to have arisen when A blood group populations in Europe migrated and mixed with B blood group populations of Asia [4].

#### **Figure 2.**

*Transfer of N-acetyl-D-galactosamine and D-galactose to a H antigen acceptor site on red blood cells (RBC) produces A and B surface antigens and blood group types, respectively. Lack of such a transfer result in an unmodified ABO H antigen precursor and the O blood group type.*


#### **Table 1.**

*The main ABO groups and their subtypes.*

Due to the association between clotting and ABO blood group, these geographic and racial differences may contribute to ethnic differences seen in rates of CVD.

## **3. ABO blood groups and arterial diseases**

There have been numerous retrospective and prospective studies and meta-analyses demonstrating an association between non-O blood groups and CVD events [5, 8–12, 24]. These studies have consistently demonstrated an association between non-O blood groups and an increased risk of arterial disease including myocardial infarction, coronary heart disease, peripheral arterial disease, and ischaemic stroke (**Table 2**). Possible mechanisms for an association with CVD include vWF-related thrombosis and modulation of platelet function through other platelet proteins which also express ABO antigens such as glycoprotein IIb [5]. The following two sections discuss the relationship between ABO blood groups and arterial diseases.


*Are ABO Gene Alleles Responsible for Cardiovascular Diseases and Venous Thromboembolism… DOI: http://dx.doi.org/10.5772/intechopen.100479*

*ACS = acute coronary syndrome; C = control subjects; CVD = cardiovascular disease; HR = heart rupture; MI = myocardial infarction; OR = Odds Ratio; PAD = peripheral arterial disease; SCANDAT = Scandinavian Donations and Transfusions; y = years.*

#### **Table 2.**

*Subject characteristics and non-O versus O blood group findings for the studies presented in the ABO blood groups and arterial diseases section (by year of publication).*

## **4. ABO and coronary artery disease**

In 1971, Medalie et al. reported the findings of a five-year prospective study of 10,000 Israeli male government employees aged ≥40 years who were born in six different regions (Eastern, Central and South-eastern Europe, Israel, Asia, and North Africa) [24]. The study found that subjects with blood groups A1, B, and A1B tended to have higher rates of myocardial infarction and those with A1 and B had higher rates of angina pectoris when compared to other blood groups [24]. Further, subjects who were negative for the Kidd glycoprotein (JKa−), a red blood cell urea transporter, had the highest rates of myocardial infarction and angina pectoris and adding this group to the ABO system (A1Jka−, BJka− and, particularly, A1BJka−) was associated with very high incidence rates [24].

A pooled analysis of two large prospective United States (US) cohort studies, the Nurses' Health Study (NHS) which included 62,073 women and the Health Professionals Follow-up Study (HPFS) which included 27,428 men, both of which had >20 years follow-up, also found that the ABO blood group was significantly associated with an increased risk of coronary heart disease for men and women [11]. A limitation of these two patient cohorts was the self-reporting of ABO and Rh factor status. However, a validation analysis of a subsample of 98 subjects found a 93% serologically confirmed ABO consistency for NHS and 90% consistency for HPFS. The combined analysis found that those with blood group A, B or AB were more likely to develop coronary heart disease and this risk was independent of age, level of physical activity, alcohol or smoking consumption or diabetes history [5, 11]. A meta-analysis, performed by the same authors, of 7 cohort studies including NHS and HPFS which combined a total of 114,648 individuals and 5,741 coronary heart disease cases found a significant pooled relative risk for coronary heart disease in patients with a non-O blood group of 1.1 (95% CI 1.05–1.18, p = 0.0001). Subjects with an O blood group had a lower risk for coronary heart disease when compared to B or AB with a trend seen for blood group A [5, 11].

ABO blood group status may be clinically relevant in subjects with concurrent cardiovascular risk factors. A study of 289 Italian blood donors with a high cardiovascular risk score (≥20) found that those with a non-O blood group had an increased risk of CVD events (including acute coronary syndrome, cerebral ischaemia, cardiac arrhythmias and supraaortic trunk or iliac artery stenosis) during a median follow-up of 5.3 years [6]. ABO blood group status may also influence CVD-related patient outcomes. In a study of 1209 patients with acute myocardial infarction, Lin et al. found a higher rate of spontaneous recanalization following myocardial infarction in association with the O blood group whereas the rate of spontaneous recanalization was lower in subjects with an A blood group [28]. Blood group A type has also been associated with an increased risk of heart rupture following myocardial infarction [29]. Hence, ABO blood type may not only predispose susceptible individuals to an increased risk of CVD events but may also influence post-myocardial infarction outcomes.

#### **5. ABO, stroke, and arterial disease in general**

ABO blood group status has been shown to influence stroke risk. An association of AB blood group with stroke (adjusted Hazards Ratio [aHR] 1.83, 95% CI 1.01–3.30) was found in the (Reasons for Geographic And Racial Differences in Stroke [REGARDS]) study which involved 30,239 US participants followed up over 5.8 years [12]. This finding remained significant after adjustment for age, gender, race region and Framingham stroke risk factors (systolic blood pressure, taking

*Are ABO Gene Alleles Responsible for Cardiovascular Diseases and Venous Thromboembolism… DOI: http://dx.doi.org/10.5772/intechopen.100479*

antihypertensive medication, diabetes, current smoking, atrial fibrillation and left ventricular hypertrophy). The association was greater in those participants without diabetes mellitus (aHR 3.33 95% CI, 1.61–6.88). Factor VIII levels accounted for 60% of the AB associated stroke risk [12]. Another study by Wiggins et al. identified an increased risk of ischaemic stroke in subjects with a B blood group (OR 1.59, 95% CI 1.17–2.17) [30].

Meta-analysis studies have also demonstrated associations between non-O blood groups and arterial diseases in general. Chen et al. performed a meta-analysis of 17 studies involving 225,810 participants and found that blood group A was associated with an increased risk of coronary artery disease (OR 1.14, 95% CI 1.03–1.26, p = 0.01) and blood group O a lower risk (OR 0.85, 95% CI 0.78–0.94, p < 0.001) [9]. These results remained significant after cases of myocardial infarction were excluded. Wu et al. conducted a systematic review and meta-analysis of 59 studies, both retrospective and prospective, reporting associations of ABO blood groups and arterial disease [8]. They found significant ORs of 1.25 (95% CI 1.14–1.36) for myocardial infarction (n = 22 studies), 1.45 (95% CI 1.35–1.46) for peripheral arterial disease (n = 8 studies) and 1.14 (95% CI 1.01–1.27) for cerebral ischaemia of arterial origin (n = 7 studies) in subjects with a non-O blood group [8].

### **6. ABO blood groups and venous thromboembolism**

The relationship between the ABO blood groups and VTE is most probably stronger than that seen in arterial diseases [5]. The association between blood group subtypes and VTE has been well documented in a few genome-wide association (GWAS) [5, 31, 32], meta-analyses and/or case–control studies [7, 8, 10, 13] (**Table 3**). A French GWAS study involving 419 patients with early age onset of first deep vein thrombosis (DVT) who were compared to 1228 controls found that participants with blood type O had a 67% lower risk of VTE compared to n those with a non-O blood group [5, 31]. Relative to other non-O groups, subjects with the uncommon A2 subtype had a 47% lower risk [5, 31]. In the same study, Factor V Leiden mutations were also associated with increased risk of VTE although the authors did not investigate the potential for an additive risk in those having both a non-O blood group and a Factor V Leiden mutation [31]. A similar association of non-O blood group with VTE was found in another GWAS study comparing 1503 VTE subjects to 1459 age and gender matched controls [32]. In this study, the population attributable risk for VTE was highest for the non-O blood group, followed by blood type A, Factor V Leiden, and prothrombin G20210A [32].

There is evidence that the A2 subtype of blood group A is associated with a lower VTE risk when compared to the A1 allele [5, 33]. The A2 allele possesses a single base deletion near its carboxyl terminal (1061delC) which results in 30 to 50-fold less A-transferase activity than its A1 counterpart which suggests a correlation between the degree of H antigen glycosylation and VTE risk [33]. Data from 2 population-based case control studies that included 504 post-menopausal women with non-fatal VTE found that the B and AB blood groups were both associated with an increased risk of VTE (OR 1.82, 95% CI 1.29–2.57, and OR 2.7, 95% CI 1.73–4.21, respectively) when compared to O1O1 subjects [30]. Participants with A11, a subtype of the A1 allele, also carried a 79% increased risk of VTE (OR 1.79, 95% CI 1.41–2.26) [30]. An increased VTE risk was also identified in a populationbased case control study of venous thrombosis (Leiden Thrombophilia Study) [34]. In this study, an increased thrombotic risk was found for non-O blood groups apart from those with genotypes homozygous to A2 or possession of any A2/O combination. Subjects with A1B/A2B and A1A1/A1A2 blood group genotypes had a 90–110%


*C = control subjects; DVT = deep vein thrombosis; FVL = Factor V Leiden; GWAS = genome-wide association study; LETS = Leiden Thrombophilia Study; MP = menopausal; OR = Odds Ratio; PTE = pulmonary thromboembolism; SCANDAT = Scandinavian Donations and Transfusions; VTE = venous thromboembolism; y = years.*

#### **Table 3.**

*A summary of subject characteristics and non-O versus O blood group findings for the studies presented in the ABO blood groups and VTE section (by year of publication).*

increased risk and those with BB/BO1/B02 genotypes had a 60% increased risk when compared to the OO genotype [34].

In a pooled analysis of 6 case–control/prospective studies of VTE, the A2 subgroup was found to be associated with a modest increase in VTE risk (OR 1.2) whereas the A1 and B subgroups had a 1.8-fold increased risk compared to the O1 subgroup. In contrast, O2 had a relative protective effect (OR 0.8) [7]. Both the A1

#### *Are ABO Gene Alleles Responsible for Cardiovascular Diseases and Venous Thromboembolism… DOI: http://dx.doi.org/10.5772/intechopen.100479*

and B subgroups were associated with increased vWF and factor VIII plasma levels whereas only the A1 subgroup was associated with increased ICAM levels [7]. A meta-analysis of 21 VTE studies, 18 of which were retrospective in design, found a pooled OR of 1.79 (95% CI 1.56–2.05) for non-O blood group and VTE [7]. The combination of A1A1/A1B/BB genotypes had an OR of 2.44 (95% CI 1.79–3.33) and A1O/BO/A2B an OR of 2.11 (95% CI 1.66–2.68) for VTE [8].

The presence of a non-O blood group has been found to correlate with unprovoked PTE, provoked including pregnancy induced and recurrent VTE. In a Scandinavian 25-year follow-up study of >1.6 million blood donors, those with a non-O blood group had higher rates of pregnancy-related VTE events, DVT and pulmonary embolism [10]. The risks of recurrent pulmonary embolism and DVT provoked by comorbid illness were also higher in subjects with a non-O blood group [10]. A large hospital-based retrospective study of 200,660 Han Chinese patients including 1412 VTE subjects (600 with DVT, 441 with pulmonary embolism and 371 with both conditions) conducted between 2010 and 2016 found a significant association of non-O blood group with VTE (OR 1.35, 95% CI 1.21–1.54) [13]. Interestingly, subgroup analysis found a relatively greater non-O blood group risk for those with an unprovoked VTE (OR 1.86) compared to provoked VTE (OR 1.22). The OR for having a non-O blood group also appeared to decrease with age [13]. Finally, a Brazilian case control study comparing 65 subjects with a history of DVT to 51 controls showed a significant increased risk of VTE in the presence of Factor V Leiden mutation (OR 10.1) which doubled in those in whom the AB allele of the ABO blood group was also present (OR 22.3) [17].

Future research into the role of developing risk stratification models or algorithms, for example, by combining ABO and other genetic variables with patient comorbidity and arterial risk factors to identify individuals at higher risk of VTE is warranted. This may translate to improved cardiovascular disease management including decision making for VTE prophylaxis at the hospital and outpatient setting.

## **7. Von Willebrand factor, factor VIII and other factors associated with ABO blood group and CVD**

The majority of studies that have been presented in this review implicate an increase in plasma levels of vWF and factor VIII by non-O blood group types as the likely mechanism for an increased risk of thromboembolic events [5–13]. VWF/ factor VIII are important in the acute phase response to vessel injury [8]. VWF is a carrier of factor VIII, protects it from inactivation, can also recruit platelets to a site of vessel injury to induce a coagulation cascade responsible for clot formation [5]. VWF can also bind to the platelet receptor glycoprotein Iba, to form a bridge between platelets and the endothelium and participate in a thrombo-inflammatory response (**Figure 3**) [35, 36].

ABO blood groups may have a direct functional effect on circulating vWF and thereby modulate both vWF and factor VIII levels [5]. The mechanism by which the presence of an N-acetyl-D-galactosamine or D-galactose residue on glycans expressed on the H antigen acceptor site of a RBC influences plasma levels and/ or bioactivity of vWF is unclear [16]. A plausible mechanism is that ABO glycans on vWF itself influence its release into plasma and/or its clearance [16]. VWF is derived from a pre-pro-polypeptide (ppvWF) synthesized in endothelial cells and megakaryocytes [16]. The expression of blood antigen A on vWF correlates with decreased ppvWF to vWF ratios as well as longer half-life and increased plasma levels of vWF [16].

#### **Figure 3.**

*Von Willebrand factor (vWF) can bind to the platelet receptor glycoprotein Ib (GPIb) to form a bridge between platelets and the endothelium and a thrombo-inflammatory response. The protease ADAMTTS13 (***a d***isintegrin* **a***nd* **m***etalloproteinase with a* **t***hrombo***s***pondin type 1 motif, member* **13***) is responsible for the proteolysis and clearance of vWF from the circulation.*

It has been postulated that the presence of A and B terminal carbohydrate antigens influence the proteolysis of vWF by its major protease ADAMTTS13 (**a d**isintegrin **a**nd **m**etalloproteinase with a **t**hrombo**s**pondin type 1 motif, member **13** - also known as von Willebrand factor-cleaving protease [VWFCP]) [5]. Individuals lacking glycosyltransferase activity (O blood group) have higher levels of ADAMTS13 activity suggesting that ABO glycosyltransferase activity can indirectly modify, for example, inhibit proteolytic activity and reduce vWF clearance from the circulation [5]. However, there are studies which have not supported this as the underlying mechanism [37]. Future research into other, yet to be determined, ABO blood group and VWF-related associations may unravel the underlying mechanism of a non-O blood group increased risk of thrombosis.

Blood group antigens are also associated with elevated plasma levels of markers of inflammation including endothelial cell and platelet-derived adhesion molecules [5]. Elevated plasma levels of adhesion molecules including soluble P-selectin, soluble ICAM-1 and tumour necrosis factor-alpha are associated with ABO genotype, which may result in arterial and venous thrombosis and an increased CVD risk [5, 11]. However, in studies reporting the circulating expression levels of sICAM-1 and soluble P-selectin, the blood group A has paradoxically been found to be associated with lower circulating expression levels of sICAM-1 and soluble P-selectin when compared to the O blood group [38, 39]. This contradictory finding has been described in healthy Chinese populations and a study of Caucasian women without a history of chronic disease [38, 39]. A postulated explanation for why blood group A, in general, may be associated with lower circulating inflammatory markers despite carrying a higher CVD risk is that higher levels of sICAM-1 or soluble P-selectin expression are limited to those with significant CVD risk factors and/ or symptomatic CVD. The concentrations of membrane forms of these adhesion

*Are ABO Gene Alleles Responsible for Cardiovascular Diseases and Venous Thromboembolism… DOI: http://dx.doi.org/10.5772/intechopen.100479*

molecules may also higher and thereby still mediate leucocyte migration and adhesion at an endothelial level [39]. It is also possible that reduced levels of sICAM-1 increase the adhesion of leukocytes on endothelial surfaces which may result in increased arterial inflammation [40].

Platelet glycoproteins including GPIIb, and platelet endothelial cell adhesion molecule are known to carry ABO blood group antigens and may be involved in thrombosis through modulation of the GPIIb-GPIIIa fibrinogen receptor complex [5]. A relationship between ABO blood group and angiotensin converting enzyme activity has also been reported which implicates a role for ABO blood group in the regulation of arterial risk factors such as hypertension [41].

Epidemiological studies have demonstrated an association between an elevated serum cholesterol including low-density lipoprotein cholesterol and non-O blood groups [5, 42]. These findings implicate ABO genotypes in the modulation of plasma lipids. ABO blood groups are also associated with phytosterol levels which have also been reported to modify cardiovascular risk [5].

## **8. ABO blood group, COVID-19, and CVD**

There is growing evidence that ABO blood groups may play a role in the susceptibility to and severity of SARS-CoV-2 infection [18–20]. Individuals with blood group O have a lower risk and those with blood group A carry a higher risk of SARS-CoV-2 infection [18]. A systematic review by the International Society of Blood Transfusion (ISBT) COVID-19 working group recently reported that subjects with blood group A had a higher rate of SARS-CoV-2 infection as well as an increased risk of requiring mechanical ventilation, continuous renal replacement therapy and prolonged intensive care unit stay [18]. Postulated mechanisms include an increase in angiotensin converting enzyme-1 levels in blood group A patients and an increased risk of cardiovascular, thromboembolic, and inflammatory complications [18]. It is plausible that possession of a non-O blood group and associated increase in vWF and factor VIII levels have an additive effect to the thrombophilia caused by SARS-CoV-2 and results in an increased risk of COVID-related CVD complications [18–20]. A recent hypothesis for an association between non-O blood group type and risk of SARS-CoV-2 infection is that anti-A and/or anti-B antibodies, which are present in patients with blood group O bind to a corresponding antigen, for example the angiotensin-converting-enzyme-2-receptor, on the SARS-CoV-2 viral envelope which then inhibits viral entry into lung epithelium (**Figure 4**) [18]. Although ABH antigen structures are yet to be described on the SARS-CoV-2 protein, the spike protein has been reported to possess N-glycans and N-glycosylation sites which could potentially interact with anti-A and anti-B antigens and thus confer protection against infection in individuals with the blood group O type [18]. The possibility that blood group A patients also have higher rates of underlying comorbidities which significantly contribute to COVID-related complications cannot be excluded [18].

A single-centre study from Bangladesh which evaluated 438 patients with SARS-CoV-2 infection also found a significantly higher rate of blood group A amongst COVID-19 patients compared to the general population [20]. However, ABO blood groups were not associated with type of presentation or recovery from infection [20]. Conversely, an observational study of 14,112 individuals tested for SARS-CoV-2 in the New York Presbyterian hospital system found that risk of intubation was increased for AB and B blood groups but decreased for A when compared to O blood group and risk of death was increased for those with AB blood group and decreased for A and B blood groups [19]. Interestingly, Rhesus status, which is not implicated

#### **Figure 4.**

*A hypothesis for an association between non-O blood group type and risk of SARS-CoV-2 infection is that anti-A and/or anti-B antibodies may bind to the angiotensin-converting-enzyme-2-receptor on the SARS-CoV-2 viral envelope and thereby inhibit viral entry into lung epithelium. Top left shows blood group O with anti-A and anti-B antibodies in the plasma. Top right illustrates anti-A antibodies of blood group O which potentially competitively bind to the spike protein of SARS-CoV-2 and thus inhibit infection. Lower left shows blood group A with A-antigens on the membranes of red blood cells. Lower right depicts ABH glycans on the SARS-CoV-2 spike protein which potentially competitively bind to angiotensin converting enzyme 2 (ACE2) receptors.*

in CVD risk, correlated with COVID-19 risk [19]. Rhesus-negative subjects had a lower risk of SARS-CoV-2 infection, intubation, and death [19]. The mechanism of the relationships of ABO blood group, Rhesus status and SARS-CoV-2 infection is unknown. Further research into the relationship between blood groups and risk of SARS-CoV-2 infection and COVID-19 related complications is warranted.

## **9. Minor blood group antigens and CVD**

There are over 35 minor blood group antigens on red blood cells [21], some of which including P and Lewis, are widely distributed in other human cells and body fluids [43, 44]. Minor blood groups have been associated with several diseases ranging from malignancy to peptic ulcer disease, infection and CVD [43, 44]. As discussed previously, subjects with a combination of blood groups A or B and the Kidd antigen Jka− status have been shown to be at increased risk of myocardial infarction [24]. Sialyl-Lex (sLex ), an antigen of the Lewis blood group system, is a major ligand for the cellular adhesion molecules E, P and L-selectin which are involved in the adhesion of leucocytes to endothelium [44]. The Duffy blood group glycoprotein is a chemokine receptor on RBCs that is involved in the recruitment

#### *Are ABO Gene Alleles Responsible for Cardiovascular Diseases and Venous Thromboembolism… DOI: http://dx.doi.org/10.5772/intechopen.100479*

of leucocytes to sites of inflammation [44]. Although the exact mechanisms are unclear, these biological characteristics offer explanation why the Lewis and Duffy blood group antigens may be associated with an increased risk of CVD.

The Lewis blood group system, which was first discovered by Mourant in 1946, is classified into four phenotypes [Le(a-b-), Le(a + b-), Le(a-b+), Le(a + b+)] determined by two genetic systems closely related on the short arm of chromosome 19 [45]. In a study of 3385 Danish males, the Le(a-b-) phenotype was associated with an increased risk of mortality from ischaemic heart disease [46]. In another Danish study involving 702 participants (72% male), the Le(a-b-) was associated with self-reported non-fatal stroke [47]. However, a North Indian cross-sectional study that compared 161 patients with angiographically-proven coronary artery disease with 71 control subjects with normal angiography, found that the lack of Lewis antigen expression was associated with coronary artery disease in female subjects only [48]. A lack of Lewis antigen expression has also been associated with a higher body mass index, weight gain over time, a lower level of physical activity, type 2 diabetes mellitus and hypertriglyceridemia all of which associated with an increased risk of CVD [49–52].

The Duffy antigen, located on the long arm of chromosome 1 [53], has also been implicated in CVD risk [54]. There are four Duffy phenotypes [Fy(a-b-), Fy(a + b-), Fy(a-b+), Fy(a + b+) [53]. A study of 5301 African American participants found that Duffy negative subjects with a neutrophil: lymphocyte ratio ≥ 1.77 were more likely to have coronary artery disease and stroke [54]. Lack of Duffy expression has also been associated with chronic organ damage, in particular renal dysfunction, in subjects with sickle-cell disease [55].

To the best of our knowledge, there have been no studies to date addressing the relationship of minor blood groups and COVID-19.

The limitations of studies evaluating the role of minor blood groups in CVD include their observational cohort design, case selection, outcome definitions, cohort sizes and influence of population attributable factors.

## **10. Conclusion**

Subjects with non-O blood group type have an increased risk of arterial and venous thromboembolism. Blood groups A1, B and AB are at particularly increased risk of CVD events whereas blood group O confers a protective effect. Postulated mechanisms of underlying the relationship between ABO blood group and CVD include vWF and factor VIII activity and elevations in circulating inflammatory markers and plasma lipids. Comorbidities including arterial risk factors and predisposing factors to VTE such as concomitant Factor V Leiden mutations may have an additive effect to thromboembolic risk. Minor blood group types including Kidd, Lewis and Duffy are also been associated with CVD. The relationship of non-O blood group type and SARS-CoV-2 infection warrants further research. Future directions include the development and implementation of risk stratification algorithms for thromboembolic risk such as ABO blood group and other factors associated with arterial or venous disease in a hospital or outpatient setting.

## **Author details**

Dennis J. Cordato1,2,3, Wissam Soubra3,4,5, Sameer Saleem1,2,3 and Kaneez Fatima Shad3,5,6\*

1 Department of Neurophysiology, Liverpool Hospital, NSW, Australia

2 South Western Sydney Clinic School, University of New South Wales, Sydney, NSW, Australia

3 Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia

4 A Healthy Step Clinic, NSW, Australia

5 School of Life Sciences, University of Technology Sydney, NSW, Australia

6 School of Behavioural and Health Sciences, Faculty of Health Sciences, Australian Catholic University, NSW, Australia

\*Address all correspondence to: kaneez.fatimashad@uts.edu.au; ftmshad@gmail.com

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Are ABO Gene Alleles Responsible for Cardiovascular Diseases and Venous Thromboembolism… DOI: http://dx.doi.org/10.5772/intechopen.100479*

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## **Chapter 2** Human Blood

*Francisca Varpit and Vela Galama*

## **Abstract**

The human blood is composed of 3 layers of humors when separated into its different components. The component that is clear, slightly yellow (plasma), the whitish viscous-like (buffy coat) and the red fluid (red cells). The plasma component is composed of proteins; however, it will not be discussed in this chapter. The buffy coat is composed of white blood cells and platelets. The white blood cells are composed of granulocytes and agranulocytes; all of which take part in immune defense. The granulocytes, including monocytes have non-specific immune response while agranulocytes, which include B and T cells have specific immune response. The platelets function to help maintain normal hemostasis during vascular injury. Blood group antigens are found on the surface of red cells and are composed of proteins, carbohydrates and lipids. They are mostly inherited on autosomes with the exception of two which have been found to be inherited on the X chromosomes. With the advance of technology, some of their physiological functional roles have been elucidated. These include; structural integrity, cationic exchange, transporters, adhesion and receptor functions, and cell to cell communication. However, these mechanisms have been capitalized by infectious agents to gain entry to the human body causing disease.

**Keywords:** human blood, blood components, red cell membranes, blood group systems, blood group antigens, physiological functions, pathophysiological functions

## **1. Introduction**

Since ancient times, blood has been viewed as the very essence of human life. In fact, description of the human blood dates back to the writings of Hippocrates in about 400 B.C. He described it as being composed of four layers of fluid; one that looked "black bile, red blood, whitish viscous-like (phlegm) and yellow bile" [1]. This was later clarified in the twelfth century by a Swedish physician as a description of blood that is undergoing clotting process, where blood is being separated into distinct portions. During this time and earlier, the state of health and disease were thought to have been caused by an imbalance between these layers of blood. This helped to explain why bloodletting was performed during those ancient times and into the nineteenth century [1, 2].

During those early years (200 AD), red blood was taught to be the dominant humor and therefore bloodletting was carried out to reduce excess blood from circulation, to slow down the heart rate, and also to reduce an inflammatory process in an individual suffering from an inflammation. It was believed that this process would in turn bring balance to the different layers of blood, and ultimately health to the individual being bled [2].

The composition of blood was however not known, until the discovery of the microscope in 1673 by Anton Leeuwenhoeck. By 1683, Leeuwenhoeck could see minute microorganisms such as bacteria using the instrument [3] and even accurately described and measured red blood cells [1]. During this time, bloodletting was based on unscientific principles and therefore remained controversial.

However, with the advance of technology at the turn of the twentieth century, new approaches and standardized methods were developed, which contributed to better understanding of the composition and structural organization of red cells [4]. This eventuated in the current acceptance of Bloodletting as a therapeutic treatment for specific chronic diseases associated with hematochromatosis (iron overload), erythrocytosis (elevated hematocrit), porphyria and polycythemia (excess number of red cells) [3].

As a result of advance in technology, there was also the understanding that red blood cell membranes are composed of protein and lipid residues, which define their structural composition, physiological and biological roles. Much of their protein content is made up of hemoglobin; essential for transportation of oxygen (O₂) to tissues and carbondioxide (CO₂) to the lungs. Apart from transportation, they have other physiological functions such as; maintaining structural integrity of the cell, modulation of cell-cell interactions or vascular endothelium-cell interactions, anchorage site of cystoskeleton, anion exchange, adhesion and receptor functions [4]. It is now well understood that, apart from these normal physiological functions, red cells also serve as biological mediums by which external invaders can enter blood circulation and tissues to cause disease to the human body [5]. Their pathophysiological roles are discussed in Section 4, Subsection 4.2.

## **2. Blood Components**

#### **2.1 Composition**

Blood does not only contain fluid but also other substances such as proteins, carbohydrates, lipids and antigens [4]. The blood is comprised of 55% plasma and 45% formed or cellular elements [6]. The formed or cellular elements include buffy coat, which contains white blood cells (WBCs) and platelets, and red blood cells (**Figure 1**). Blood is essential in humans and other animals and performs multiple tasks. The erythrocytes or red blood cells contain hemoglobin and function in the

#### **Figure 1.**

*Blood, when centrifuged, it is separated into 3 different layers; plasma (contains proteins), Buffy coat (contains mainly white blood cells and platelets), and red cell concentrate) [7].*

### *Human Blood DOI: http://dx.doi.org/10.5772/intechopen.102293*

transport of oxygen (O2) to tissues and carbon dioxide (CO2) from tissues to the lungs. The WBCs (Leucocytes)) are involved in the body's defense against the invasion of foreign antigens. The Platelets (thrombocytes) are involved in the process of hemostasis; prevention of blood loss during injury [6–8].

## **2.2 Synthesis of blood components**

All human blood goes through a process known as hemopoiesis or hematopoiesis. Hematopoiesis or hemopoiesis is the process of blood production. This process proceeds through different stages starting from early embryonic life (mesoblastic stage), to the hepatic stage, and then to the myeloid stage. The process in the embryonic and early foetal life occur in the yolk sac, although at this stage, only the very early red cells (erythroblasts) are formed. As the foetus develops, all blood cells are formed in the foetal liver. Apart from the yolk sac, hemopoiesis also occurs in the mesoderm of intraembryonic aorta/gonad/mesonephros (AGM) region. After several weeks, it also occurs in the spleen, lymph nodes and thymus. From the third to the 4th month until birth, blood cell production occurs exclusively in the bone marrow. As the child matures into adulthood, blood cell production is confined to only the flat bones such as; the sternum, ribs, iliac bones, vertebrae, and proximal ends of long bones (**Figure 2**) [7, 8].

## *2.2.1 Red blood cells (Erythrocytes)*

Mature red blood cells (RBCs) or erythrocytes are very small cells with a diameter of about 8.0 μm. They maintain a biconcave discoid shape and do not contain a nucleus [9]. The life span of mature RBCs is about 120 days. After the 120 days, they are phagocytosed by reticuloendothelial system (RES) macrophages in the spleen [8]. Their main function is to transport O₂ from the lungs to various tissues and organs and from these tissues and organs, it carries CO₂ to the lungs for reoxygenation [7, 9, 10].

#### **Figure 2.**

*The phases of hematopoeisis. During the process of blood production, erythroblasts are the first to be formed in the yolk sac, followed by the rest of the cell lines in the fetal liver, then in the spleen and finally in the BM from the 4th month of life onwards to adulthood [7].*

## *2.2.2 White blood cells*

White blood cells are categorised as granulocytes and agranulocytes. Granulocytes include; neutrophils, eosinophils and basophils, and agranulocytes include; lymphocytes and monocytes [9, 11].

## *2.2.2.1 Granulocytes*

These are also called polymorphonuclear leucocytes because their nuclei are oddly shaped and their cytoplasm have densely stained granules when stained with Leishman's stain or Wright-Giemsa stain. They play a major role in immune defence as part of the innate immune system. Their role in defence is non-specific, short-lived and without memory [11].

## *2.2.2.1.1 Neutrophils*

Neutrophils make up 97% of the granulocyte lineage and are the first to arrive at sites of infection. The size of a mature neutrophil is about 10 to 12 micrometres (μm), with 2 to 5 lobes of deep purple nucleoli when stained with Leishman's stain. They also have very fine light pink cytoplasmic granules. These granules contain proteins and enzymes such as; lysozyme, lactoferrin, vitamin B₁₂-binding protein, myeloperoxidase, acid phosphatase, elastases and others. Their major roles are; phagocytosis of bacteria, viruses and yeasts, formation of Neutrophil Extracellular Trap (NET), degranulation and cytokine production [11, 12]. Their lifespan is 1–2 days in peripheral blood circulation [7, 8].

## *2.2.2.1.2 Eosinophils*

Eosinophils are small bilobed granulocytes, with granules that stain red orange with the Wright-Giemsa stain. These granules contain proteins and enzymes such as the major basic protein, cationic proteins, peroxidase and histaminase. These are used to defend against helminthic parasites. On activation, eosinophils produce debilitating toxic respiratory burst and also create transmembrane plug that kill their target. Their maturation in the BM takes 2 to 6 days and their lifespan in blood is less than 8 hours [7–9].

## *2.2.2.1.3 Basophils*

Basophils are the least numerous of the circulating WBCs. Their nucleus contains condensed chromatin, shrouded by darkly stained coarse granules when stained with the Wright-Giemsa stain. These granules contain inflammatory mediators and proteins such as; histamine, serotonin, heparin, Major Basic protein, and enzymes such as DNAases, proteases and lipases. They also express receptors to IgE and therefore have the ability to become activated when bound to IgE-Antigen immune complexes. On activation, they degranulate releasing their content that kill their target [12]. They also play a role in hypersensitivity reaction. Their lifespan is less than 3 days [13].

## *2.2.2.2 Agranulocytes*

These cells do not contain multiple lobes like the granulocytes.

## *2.2.2.2.1 Lymphocytes*

There are two types of lymphocytes. These are B and T lymphocytes. They are the major players in the adaptive immune response against foreign invasions. They constitute 20–30% of the total WBC population. Unlike the granulocytes, their actions are slow, specific and have memory [12]. The B cells function to produce antibodies and the T cells function to provide help to B-cells for antibody production, kill off virus-infected cells, and also play regulatory roles. The sizes of these cells range from 8 to 10 μm [7–9]. Naïve lymphocytes live longer in their restful state than effector lymphocytes. Lymphocytes that have differentiated into memory cells have longer lifespan. The different lifespan periods are dependent on heterogeneous populations during stages of differentiation and activation [14].

## *2.2.2.2.2 Monocytes*

Monocytes are usually large in size, measuring about 12–20 μm in diameter. The nucleus is generally kidney-shaped with fine chromatin. They have abundant cytoplasm which appear blue, and often contain azurophilic granules and vacuoles. They circulate in blood for about a day before they exit to tissues where they are called macrophages or histiocytes [12]. In the blood, their function is to protect against bloodborne pathogens. In tissues, their major roles are phagocytosis, antigen presentation, cytokine production and NET formation [7–9]. This population of cells comprise a heterogeneous population; distinguishable by their cell surface markers and functions. A blood classical monocyte's lifespan is ~1.0 day, a blood intermediate monocyte's life span is ~ 4.3 days and a non-classical blood monocyte's lifespan is ~7.4 days [15].

## *2.2.3 Platelets*

Platelets are the products of cytoplasmic fragmentation of megakaryocytes in the BM in a process called megakaryopoiesis [12]. The diameter of platelets is about 2–3μm. They contain α-granules, dense granules, and lysosome. Their main function is their synergistic interactions with endothelial wall and plasma proteins to maintain normal hemostasis during vascular injury. They remain alive in the blood for about 10 days [7–9].

## **3. Blood group antigens**

The term "blood group" generally refers to a person's collection of "red cell surface antigens". These are found on the surface of red blood cells as part of the red cell membrane. They are made up of proteins, glycoproteins and glycolipids. These may elicit an immune response in individuals lacking these antigens.

Blood group antigens have been classified by the International Society for Blood Transfusion (ISBT) into 30 blood group systems [16–18]. However, as of June, 2019, there are currently 38 blood group systems (**Table 1**), with over 200 red cell antigens classified under these systems, while some are classified as collections [16, 19]. These antigens are inherited and as such, understanding of their genetic makeup is important as well as their unique characteristics which differentiates one group or one antigen from another. Such characteristics include; genetic expression, structure and location on red blood cells, and the type of antibody they induce. The most common and clinically significant of these blood group antigens are the


#### **Table 1.**

*International society for blood banks (ISBT) classification of the known blood group systems with their ISBT numbers and symbols [19].*

antigens belonging to the ABO and Rhesus blood group systems because they have the potential of eliciting an immune response that can cause fatal consequences through blood transfusion and or pregnancy [16].

#### **3.1 Blood group antigen inheritance**

Genes are units of inheritance that encode particular proteins needed for production of particular inherited traits. Genetic information caried in these genes are found in double stranded deoxyribonucleic acid (DNA) called chromosomes. Humans have 23 pairs of these, of which; 22 are autosomes and 1 pair of sex chromosomes. Within these chromosomes are sites called genetic loci; where genes are located. Within these genetic loci are alternate forms of genes called "alleles" [16].

Inheritance of blood group antigens follow an autosomal codominant pattern of inheritance, where alleles inherited from both parents are equally expressed on autosomes [16]. Hereditary patterns of these antigens are based on the Mendelian principles of inheritance; which sprouted from early experiments done on pea hybrids [17]. His genetic concepts of Dominance, Independent Segregation and Assortment are currently applied in understanding inherited characteristics (traits) observed in human blood group genetics. For each inherited trait (character), there are two alleles inherited from each parent. The expression of this inherited trait is dependent on the combination of the two alleles inherited. One of these alleles suppresses the effect of the other, while the other allele can only be observed in the absence of the dominant allele. The allele that suppresses the expression of the other *Human Blood DOI: http://dx.doi.org/10.5772/intechopen.102293*


**Table 2.**

*This Punnett square describes Mendel's concept of "independent segregation" using symbolic "A" and "a" to denote inheritance of a dominant allele and a recessive allele respectively [17].*

is called the dominant gene, while the other that is not expressed in the presence of the dominant gene is called recessive. This concept is referred to as the Law of dominance [16, 17].

Thus, alleles inherited from each parent can be the same (homozygous) or different (heterozygous). The concept of independent segregation refers to each parent having a set of alleles for a particular trait, either of which can be passed onto the next generation. These alleles segregate, allowing for only one allele to be transmitted to an offspring. For example, using the letters "A" and "a" to represent a dominant and a recessive allele respectively, there are four possible combinations (**Table 2**). The AA combination constitutes entirely of AA (homozygous) offspring and the aa combination comprise entirely of aa (recessive) offspring. The offspring of the aa allele combination differ from the AA, aA and Aa combination due to the absence of a dominant allele. The offspring of Aa and aA (heterozygous) gene combinations inherited traits common to all four combinations [17].

Mendel's third concept is "independent assortment". During meiosis, a mixture of genetic material is produced resulting from random behavior of genes on separate chromosomes. These genes are inherited independent of each other on different chromosomes but are expressed on the same red cell membrane. **Figure 3** illustrates

#### **Figure 3.**

*Independent assortment. The ABO blood group antigens are sorted independently from the Kell antigen genes because they are inherited on different chromosomes. However, they can all be expressed on the same red cell membrane separately and discretely [16].*

#### **Figure 4.**

*Strength of immunogenicity of the Rhesus Blood Group antigens in decreasing order of immunogenicity.*

the ABO and the Kell blood group system genes, whose genes are located on chromosomes 9 and chromosome 7 respectively [16].

Genes coding for most of these blood group antigens are inherited on autosomes except the Xg and the Kx. The Kx is coded for by the Xk gene, while the Xg is coded for by the Xgᵅ allele, both of which are located on the X chromosome. This means that fathers having the latter genes would pass it on to their daughters and none to their sons. If, however, mothers have these genes, they would pass it on to both genders [16, 20].

Inheritance of blood group antigens follow distinct patterns of inheritance. Some genes code for antigens that are co-dominant., some are dominant over another and some are recessive. For example, in the ABO blood group system, the A and B antigens are codominant; both alleles are expressed to show the trait. When A and O alleles, or B and O alleles are inherited, the O trait is not expressed because the A and the B alleles are dominant over the O. When O and O alleles are inherited, the O traits are observed in the absence of a dominant gene. The O gene is said to be recessive (**Figure 4**) [17].

According to the ISBT, some of these blood group antigens have been classified as blood group systems based on their serologic and molecular characteristics (**Table 1**) and their locations on specific chromosomes has also been elucidated (**Table 3**).

#### **3.2 Structure and location on red cells**

Three of the basic structural properties of red cells are hemoglobin, enzymes and the membrane [18].

#### *3.2.1 Hemoglobin*

Although mature red cells no longer have nucleus nor mitochondria, they have an abundance of hemoglobin, a red pigment that contains oxygen. The hemoglobin carries oxygen to all parts of the body to keep the body alive and collects carbon dioxide (CO₂) from the tissues to the lungs for re-oxygenation.


#### **Table 3.**

*Some of the blood group antigens and their chromosomal locations, all of which are found on autosomes and only two are found on the X (sex) chromosomes [16].*

#### *3.2.2 Enzymes*

The Embden-Meyerhof pathway is a metabolic pathway used by mature red cells to generate energy through a series of enzymatic pathways that catalyze the conversion of glucose to lactate and pyruvate. Within this pathway, there is a shunt called the Rapoport Luebering shunt that generates the production of 2,3Diphosphoglycerate (2,3DPG); important in influencing the release of O₂ in tissues. Apart from production of energy and 2,3 DPG, another end product of this glycolytic pathway is generation of Nicotinamde Adenine Dihydrogenase (NADH); necessary for reducing nonfunctional methemoglobin to oxyhemoglobin. Another metabolic pathway in red cells is the pentose phosphate shunt. Two enzymes are generated during this process. These are called glucose-6 phosphate-dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD), which then generate Nicotinamide Adenine Diphosphodehydrogenase (NADPH). This enzyme with Glutathione reductase catalyzes the generation of glutathione (GSH), which along with glutathione peroxidase function to detoxify hydrogen peroxide and thus rendering the red cell safe from oxidant damage [18].

## *3.2.3 Red cell membrane*

The red cell membrane is comprised of proteins, lipids and carbohydrates. Blood group antigens are found linked to these on the red cell membranes. Some of these red cell antigens are only found on the red cell membrane or in fluids, while some are found both on the red cell membranes and in body fluids. Those found on the red cell membrane and also in fluids are; the ABO blood group system, Hh and Lutheran. In fact, the ABO antigens are also found in lymphocytes, platelets, epithelial cells and endothelial cells and the kidney having been adsorbed from the plasma [16]. Those found on red cell membranes include; the Rhesus, Kell, Kx, Duffy and Kidd. There is one known blood group system that is unique from the others in that it is found predominantly in fluids. This blood group system is called the Lewis and it is produced by tissue cells and released into body fluids. However, these get adsorbed onto red cell membranes shortly after birth and continues on for the first 6 years of life [19]. Although it is not clinically significant, serologic antibody detected may indicate H. *pylori* infection as the Leᵇ allele has a receptor to this gram- negative bacteria [16].

Like the ABO blood group system, the Le gene does not code directly for its antigen but instead codes for a glycosyltransferase called L-fucosyltransferase, which then adds an immunodominant sugar called L-fucose to the precursor substance (H antigen) to form the Leᵅ antigen or Le (a+) phenotype. Its adsorption onto red cell membranes depends on the presence of the precursor substance (H antigens) on red cells and also presence of the L-fucosyltransferase type 1. Conversion of the Lewis antigen from Leᵅ allele to Leᵇ in secretions depends on the Secretor gene (Se). If the individual also had inherited this gene, which is mainly found in fluids, then the L-fucose is added to the precursor substance in fluids to form the Leᵇ antigen or Le(b+) phenotype. This then gets adsorbed onto red cell membrane preferably over the Leᵅ antigen [16, 20].

### *3.2.3.1 The ABO, rhesus and other blood group antigens*

Genes coding for the formation of some of these antigens do not code directly for their respective antigens. Instead, they code for glycosyltransferases, which in turn catalyze the transfer of immunodominant sugars from donor molecules to a precursor substance for the formation of their respective antigens. Examples of

these are; the H, ABO, Se, Lewis, I/i and P₁. The H, ABO and secretor (Se) blood group antigens are inter-related, in that the H antigens forms the basis for the formation of the A and B antigens on red cells and in secretions [20]. Lack of formation of the H precursor antigen on red cells result in the formation of the Bombay (OH) blood type, instead of the ABO [21]. These individuals lack the ABH antigens and thus possess naturally occurring antibodies against the A, B, O and H antigens in their plasma. This exposes them to fatal consequences during blood transfusion. The Se gene on the other hand play a vital role in the formation of ABH antigens in secretions. This is because it controls the expression of the H antigen in secretions [21]. In individuals who lack the Se genes, there is no formation of the H antigen in secretion and ultimately no formation of the A and B antigens in secretions as well.

There are however, cases where an individual inherits a dominant allele and a recessive (Sese) or co-dominant alleles (SeSe) from each parent in secretions but lacks the H gene on red cells. In such individuals, formation of the H antigen will still occur and thence formation of A and B antigens in secretions but not on red blood cells. These individuals are said to have the "para-Bombay" phenotype [22]. Some amounts of the A and B antigens may adsorb onto red cell membranes from plasma and hence are detected on red blood cells [22]. This is summarized in **Table 4**.

Some of the blood group antigen genes that code directly for the formation of their respective antigens include the Rhesus, Kell, Kidd, Duffy and MNS. Among these, the Rhesus antigens are very immunogenic because they are protein in nature, the most immunogenic of which is the Rh D, followed by the c, E, C, e. (**Figure 4**). Initially founded in 1939, the Rh blood group system is the most complex and polymorphic with about 50 well-defined related antigens assigned to its system classification by the ISBT [8, 23]. It is mostly associated with Haemolytic Disease of the Foetus/New Born (HDFN) especially in a second pregnancy of a Rh D positive child conceived in a mother who does not have the Rh D antigen. In the general population, 85% have the Rhesus D antigen, while the rest are negative for it [19, 24].

However, the Kidd, Kell and Duffy are all considered clinically significant as well because they have also been implicated in Hemolytic Disease of the Newborn and therefore recognition of antibodies against these antigens are vital in relation to blood transfusion and pregnancy [16].

After the Rhesus antigens, the Kell blood group antigens are next most immunogenic. It is associated with another blood group system called the Kx, inherited on the X chromosome. Absence of this on an individual's red cells weakens the


#### **Table 4.**

*Interaction between the ABO, H and Secretor genes depicting the expression of soluble antigens on red blood cells and in secretions [16, 22].*

#### *Human Blood DOI: http://dx.doi.org/10.5772/intechopen.102293*

expression of the Kell antigens, a condition called "Mcleod phenotype". They develop red cell abnormalities such as acanthocytosis and reticulocytosis [16, 20].

The Duffy Blood group antigens are glycoproteins found on chromosome 1. These glycoproteins span the membrane of the red cells. First defined in 1950 in a patient who was suffering from hemophilia, it is best remembered for its association with malaria. Individuals who do not possess this antigen (Fy a-b-) are protected against Plasmodium vivax and Plasmodium knowlesi infections. This blood type is common amongst African and American Blacks [16, 25]. Like the Duffy, the Kidd blood group antigens are glycoproteins but located on chromosome 18. They are not as polymorphic as the Rhesus and Kell blood group antigens. They play a role in urea transport. They have also been implicated in causing extravascular haemolysis in a delayed type of hemolytic transfusion reaction [16, 20].

Like the ABO and Lewis blood group antigens, the I blood group antigens are oligosaccharides, which along with the i antigen, exist on the ABH oligosaccharide chain precursors nearer to the red cell membrane. The i antigen on the other hand has not been assigned to a blood group system and remains as a collection. The i antigen is mostly expressed on red cells of New Born and cord blood, while the I is mostly seen in adults red cells [16, 18]. The P1PK Blood group antigens are glycoproteins and glycolipids, and like the ABO, Lewis, and I blood group antigens, they are also formed through the actions of glycosyltransferases. At birth, P1 is poorly expressed. The MNS are structurally glycoproteins; their sugar components are primarily composed of sialic acids attached to proteins which lends the negative charge of red cells [20].

#### **3.3 Antibody response to blood group antigens**

Karl Landsteiner's discovery of the ABO blood group antigens in 1900 [16, 26] was the beginning of safe blood transfusion as we know today. He began by first experimenting with his own blood and then that of his co-workers. When he began to mix serum taken from co-worker A with red cells from co-worker B, he realized that these formed clumps. When he then mixed his serum with red cells from both of his two co-workers, he recognized that he had antibodies against both. This he appropriately called blood group O, which to become the universal donor. The other two co-workers A and B, he called anti-A and anti-B respectively because their serum agglutinated when mixed with each other's red cells. In his article published in 1900 on these experiments, he added a footnote that stated "the serum of healthy humans has an agglutinating effect, not only upon animal blood cells, but frequently upon blood cells from other individuals as well" [26].

The antibodies against the ABO blood group antigens are the most clinically significant because they are pre-existing. Based on Landsteiner's rule, healthy individuals have antibodies against antigens that they do not have. This is the basis for all blood transfusions today. Patients' blood is always typed and crossmatched before they are infused to avoid fatal intravascular hemolytic transfusion reactions. An individual with blood antigen A has antibodies against the B antigen and an individual with blood antigen B on their red cell membrane has pre-existing antibodies A in their plasma. Individuals with no AB antigens on their red cells have both A and B antibodies in their plasma, while those that have both A and B antigens on their red cells, they do not have pre-existing antibodies in their plasma (**Table 5**).

Antibodies against the ABO blood group antigens are mainly of the IgM class and therefore are capable of reacting at temperatures ranging from 4°C to 22°C or room temperatures. Because of its pentameric structure, it is able to bind to 10 of these red cell antigens in at any one time. This is enough to trigger off a massive intravascular complement protein reaction via the classical pathway resulting in an


**Table 5.**

*Based on Karl Landsteiner's conclusions, healthy individuals have antibodies in their plasma against antigens that they do not have.*

acute hemolytic transfusion reaction if the wrong ABO blood is transfused to an individual with a different blood type. This type of reaction usually occurs within minutes or hours of transfusion of the wrong blood. If not stopped quickly, fatal consequences like disseminated intravascular coagulation (DIC), irreversible shock and death can occur. Antibodies against the Luᵇ antigens in the Lutheran Blood group system are also clinically significant. Although rare and mainly of the IgG class, it has been found to be associated with transfusion reactions and HDFN [16].

Auto antibodies against the P antigen is bi-phasic and it is called the Donath-Landsteiner antibody. It is referred to as bi-phasic because it is able to bind to the P1 or P2 antigens at lower temperatures especially in the extremities of the body and when warmed to warmer temperatures, the complement cascade is activated resulting in haemolysis. These antibodies are mainly associated with paroxysmal cold hemoglobinuria; a rare disorder characterized by cold associated haemolysis and hematuria [16].

Autoantibodies against the I are mainly associated with patients with Mycoplasma pneumoniae infections and cold haemagglutinin disease. In these patients, strong auto-agglutinations are observed in in-vitro analysis. In patients with disease conditions such infectious mononucleosis, lymphoproliferative disease and sometime in cold hemagglutinin disease, anti-i is usually detected.

### **4. Blood group antigens as modes of disease transmission**

For hundreds of years, the red cells were thought to be inert; with no form of biological functions. This was never been justified until in 1865, when Hoppe-Seyler discovered that in the red cells, there is an abundance of hemoglobin. These red cells have two important properties that allow them to squeeze easily through blood capillaries supplying tissues with oxygen to keep these tissues alive [1]. These are flexibility of its membrane and fluidity of its content. Any imbalance in these two properties will cause reduced survival of these red cells and removal hence by macrophages in the spleen [20].

#### **4.1 Physiological functions of red cell antigens**

Apart from the important roles in O₂ transport to tissues and CO₂ back to the lungs, production of ATP, 2,3 DPG and production of enzymes that ultimately catalyzes the biochemical processes that result in the reduction of the dysfunctional methemoglobin to oxyhemoglobin and reduced GSH, red cell antigens located on and across the red cell membranes also play other roles in many ways. Some of their known physiological functions include, gylcosyltransferases, structural maintenance of red cells, protein transportation, complement pathway molecules


#### **Table 6.**

*Putative physiological functions of some of the known red cell antigens [22].*

regulation, adhesion molecules and as microbial receptors [16, 23]. These functions are summarized in **Table 6**.

#### **4.2 Pathophysiological functions of blood group antigens**

Blood is a pharmaceutical therapy for treatment of various blood component deficiencies and blood loss. However, it is quite often forgotten that, apart from its normal biological functions, it also serves as vessel for transmission of various blood borne pathogens. It is now well documented that some blood group antigens have been found to be associated with increased susceptibility to infections [27] enhance disease progression in others [28], while in others have indicated reduced susceptibility and severity [29]. Susceptibility to infection often depends on the geography and epidemiology of the different blood group antigens [30].

Among the ABO blood group antigens, the A antigen has been shown to be associated with increased mortality from the COVID-19 than Blood groups B and O [30]. With Blood groups B and AB, they have a higher risk of suffering from thromboembolism caused by the COVID-19 infections than O because they have higher levels of von Willie Brands Factor (vWF) [31]. Blood group A has also been reported to play a synergistic effect with the Hepatitis B virus (HBV) on the risk of development of pancreatic cancer [32]. Blood group A is also found to be significantly associated with the HBV infections, while syphilis was significantly associated with the Rhesus blood group in the same study [33]. Data from one study demonstrated that Blood group B antigens are associated with lower risk of being infected with hepatitis B virus (HBV) while Group O has been demonstrated to have had a 12% risk of being infected with HBV [32]. Severity of diarrhoea caused by *Esherishia coli, Vibrio Cholerae and Helicobacter pylori* is dependent on the O blood type and Secretor status of an individual [34]. Blood group AB is associated with the severity of dengue disease in secondary infections [27]. Like the covid-19 infections, blood group O plays a protective role against severe malaria infection [35, 36]. Being a non-secretor also play a role in reducing risk of infection by the HIV-1 and also slows down disease progression. However, on the other extreme, being a Secretor promotes infections by *Haemophilus inflenzae, Neisseria meningitidis, Streptococcus pneumonie and Esherishia coli* [34].

Helicobacter *pylori* is associated with peptic ulcer, disease, gastric carcinoma and the Norwalk virus, however disease progression is enhanced in the presence of Leᵇ antigens as these serve as receptors to the bacteria [16]. Furthermore, autoantibodies against the I (autoanti-I) are increased in *Mycoplasma pneumoniae* infections and Cold haemagglutinin disease. Additionally, autoantibodies against the i antigens (autoanti-i) are elevated in infectious mononucleosis, lymphoproliferative disease and also in Cold Hemagglutinin disease. The Duffy blood group antigens on the other hand play a protective role against Plasmodium vivax (Pv) invasion [24]; a parasite species that causes malaria. This applies only to individuals who does not express the Duffy antigens (Fya-b-).

## **5. Conclusion**

The human blood is the very essence of life as it supplies the whole body with O₂ and nutrients needed for its sustenance of life. The blood group antigens are a part of this scared suspension of fluid that flows throughout the body unendingly throughout life. Carried in its membranes are the structures that can serve two purposes in a normal physiological sense and pathophysiological, in that apart from carrying out functions that sustains the livelihood of the body that carries it, it also serves as a means of entry for foreign invaders, which cause an imbalance in the normal physiological functioning of the body causing disease state.

#### **Acknowledgements**

We wish to acknowledge the contribution of Mr. Gairo Gerega of the University of Papua New Guinea School of Medicine and Health Sciences for supplying some notes on the blood group antigens.

## **Conflict of interest**

"The authors declare no conflict of interest."

## **Author details**

Francisca Varpit\* and Vela Galama Division of Health Sciences, Discipline of Medical Laboratory Science, University of Papua New Guinea School of Medicine and Health Sciences, Port Moresby, Papua New Guinea

\*Address all correspondence to: lakuadavina@gmail.com

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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## **Chapter 3**

## ABO Blood Group and Thromboembolic Diseases

*Yetti Hernaningsih*

## **Abstract**

Thromboembolic diseases are usually inherited in the family. The tendency to repeat in an individual is a phenomenon that allows it to be studied. The inheritance and recurrence of thromboembolic diseases, of course, have individual risk factors for this occurrence. In the past, the ABO blood group was only needed for transfusion and organ transplant therapy. Over time, scientists think that blood type is a risk factor for certain diseases, including thromboembolism. Many studies divide between type O and non-O blood groups, both of which are distinguished by the presence of antigens on the cell surface and antibodies in the plasma of individuals. Type O does not have A, B antigens but has antibodies against A, B antigens, and vice versa for the non-O type. Many studies have shown that the non-O blood group has a risk factor for thromboembolic diseases, commonly due to higher levels of von Willebrand factor (VWF) and factor VIII (FVIII). These thromboembolic events can occur in arteries or venous. Thromboembolic manifestations are often associated with cardiovascular diseases for arterial thrombosis; and deep vein thrombosis (DVT) and pulmonary embolism (PE) for venous thromboembolism (VTE).

**Keywords:** ABO, blood group, arteries, venous, thromboembolic diseases

### **1. Introduction**

The known blood types in the population are A, B, AB, and O. These blood types are inherited from both parents. Antigens in the ABO blood group are complex carbohydrates, found in erythrocytes, lymphocytes, platelets, epithelial and endothelial cells, and organs such as the kidneys. Soluble forms of antigen are also synthesized and secreted by tissue cells [1]. The distribution of ABO blood groups in the population depends on race. For example, in India and Mexico, blood type O is the most common. If data from countries in the world are compared, in India and neighboring countries such as Bangladesh and Pakistan, groups O and B dominate, while populations in Europe and Africa are dominated by groups O and A. This comparison explains that the heterogeneity of blood groups in different places and populations is caused by genetic and environmental factors [2].

Initially, the importance of ABO blood type is needed to obtain a match between donor and recipient in the case of transfusion or organ transplantation. Furthermore, many studies reported the association of blood type with a certain disease, especially in the distinction between blood group O and non-O. The non-O blood type has been reported to be associated with several diseases, including cardiovascular disorders, and the incidence of venous thromboembolism (VTE). The first observation on the association between ABO blood type and VTE was made in

1963 by Dick et al. who found a statistically significant predominance of group A in 461 VTE patients [2–5].

The non-O blood group was at higher risk of thromboembolism due to higher levels of von Willebrand factor (VWF) and factor VIII (FVIII). The rate of proteolytic clearance of VWF by a disintegrin-like and metalloprotease with thrombospondin type 1 motif, 13 (ADAMTS-13) was relatively lower in plasma of the non-O blood group, resulting in a longer VWF half-life in the non-O plasma group than in the O plasma group. As a result, VWF levels were 25–30% higher in non-O group plasma than in group O plasma. High levels of VWF in non-O plasma always lead to increased FVIII levels due to the physiological role of VWF as carriers of FVIII and protecting it from the proteolytic effects of ADAMTS-13. Higher VWF and FVIII levels in subjects with non-O blood groups were strongly correlated with an increased risk of venous thrombosis, a situation that led to non-O blood type being assessed as a genetic risk factor for venous thromboembolism [6].

Wu et al. result in a meta-analysis study of the association between the ABO blood group and vascular disease, the combined odds ratio of the 21 studies analyzing VTE was 1.79 (95% CI, 1.56–2.05) for the non-O versus O group. In three studies in which blood type genotypes were performed, the combination A1 A1/A1 B/BB gave an odds ratio of 2.44 (95% CI 1.79–3.33), while the odds ratio for A1 O/BO/A2 B was 2.11 (95% CI 1.66–2.68), suggesting that the risk is related to the expression of the O(H) antigen [7].

These results are similar to the study of Spiezia et al. in a retrospective case–control study conducted on Italian patients with DVT and controls, which found that non-O blood group increased the risk of DVT by 2.2-fold than individuals with group O. An up to the 7-fold increased risk of VTE was observed when the condition inherited thrombophilic (factor V Leiden, prothrombin G20210A mutations, antithrombin, protein C and protein S deficiency) were associated with non-O blood group carriers compared with non-thrombophilic group-O carriers [4].

The data presented by Spiezia et al. cautioned that the high prevalence of non-O blood type in the general population appears to be one of the most important genetic risk factors for venous thrombosis. Like inherited thrombophilic factors (i.e., factor V Leiden and the prothrombin G20210A mutation), non-O blood types are responsible for a moderate increase in the risk of VTE, and, therefore, ABO blood group testing is recommended in individuals with thrombophilia to assess risk thrombotic [7].

#### **2. ABO blood group**

The ABO blood group system was discovered by Landsteiner in 1900. A few years later, von Decastello and Sturly discovered the AB type. Landsteiner's rule stipulates that normal individuals have ABO antibodies against an antigen not found on red blood cells. Individuals with blood type A have A antigens, do not have B antigens, therefore these individuals have B antibodies. On the other hand, individuals with blood group B have B antigens, do not have A antigens, therefore they have A antibodies. The four phenotypes were derived from the two main antigens (A and B) of the system. The phenotypes are group A, group B, group AB, and group O. Individuals with blood type AB means they have A, B antigens and do not have antibodies against A, B antigens. On the other hand, individuals with blood type O have antibodies against antigens A, B and do not have antigens A, B [1]. This classification is important for the sake of blood transfusions that must meet certain requirements.

The A and B alleles are located on chromosome 9 at the ABO locus, encoding the A- and B glycosyltransferase enzymes. ABO antigens can be found on blood

#### *ABO Blood Group and Thromboembolic Diseases DOI: http://dx.doi.org/10.5772/intechopen.102757*

cells, lymphocytes, platelets, most epithelial and endothelial cells, and organs such as the kidneys. Soluble forms of antigen can be synthesized and secreted by tissue cells. Soluble antigens can be detected in all body fluids except cerebrospinal fluid. The ABO antigen attached to red blood cells is in the form of glycolipid molecules or glycoproteins, while the main soluble form is the glycoprotein form. Discussion of the ABO antigen requires an understanding of the H antigen. The H gene is located on a different chromosome from the ABO genetic locus and plays a role in controlling the production of H antigen. In addition to the ABO and H genes, the expression of soluble ABO antigens is influenced by the inheritance of the Se gene. The Se gene genetically influences the formation of ABO antigens in saliva, tears, and other body fluids. Consequently, the occurrence and location of ABO antigens are influenced by three genetically independent loci: ABO, H, and Se [1].

The antigen-building block structure for A, B, and H antigens is an oligosaccharide chain attached to a carrier molecule either a protein or lipid. The oligosaccharide chain comprises four sugar molecules linked in simple linear forms or complex branched structures. The two-terminal sugars, d-galactose and N-acetylglucosamine, are coupled in two different configurations. When carbon number 1 of d-galactose is coupled with carbon number 3 of N-acetylglucosamine, the bond is symbolized as 1 → 3. When the number 1 carbon of d-galactose is coupled with the number 4 carbon of N-acetylglucosamine, the bond is described as β1 → 4. The structure of β1 → 4 is associated primarily with glycolipids and glycoproteins on the red cell membrane, the structure of β1 → 3 is located in body fluids and secretions [1].

This transferase catalyzes the addition of certain sugar residues so that the core structure of the H glycan precursor is converted to antigen A (GalNAc 1 → 3 [Fuc 1 → 2] Galβ 1 → 4 GlcNAc 1→), or antigen B (Gal 1–3 [Fuc 1–2] Galβ 1–4 GlcNAc 1-). As a result, the A and B structures are differentiated based on a single terminal sugar (N-acetylgalactosamine versus D-galactose respectively). Individual O groups lack A- or B-transferase activity result from the inactivation of the A1 glycosyltransferase gene, and the nonreducing ends of the corresponding glycans, and therefore continue to express the basic structure of the glycan H (Fuc 1–2] Galβ 1–4 GlcNAc 1-) at the ends of their oligosaccharide chains [8, 9]. Individuals who synthesize determinant A exclusively have blood type A and have genotypes AA or AO, individuals with blood group B are BB or BO, and individuals expressing one allele A and one B have genotype AB. Individuals with blood type O expressing inactive glycosyltransferase A/B have genotype OO. They express only the H antigen. In terms of nomenclature, blood group O includes the H antigen and sometimes the term ABO(H) is used [10].

## **3. Thromboembolic diseases**

Venous and arterial thrombotic disorders have different pathophysiological entities, as a result of anatomical differences and different clinical presentations. In particular, arterial thrombosis results from the phenomenon of platelet activation, whereas venous thrombosis is largely a matter of activation of the clotting system [1].

There are fundamental pathophysiological differences between arterial and venous thrombus. Arterial thrombi which are happened in small arteries and arterioles are occlusive. Thrombus that occurs in the ventricles of the heart and the great arteries and the aorta, the common carotid artery is nonocclusive. Arterial thrombus is formed in response to increased local shear and exposure to thrombogenic material in damaged vessels, occurs in high-pressure and high-flow systems. Arterial thrombus, referred to as white thrombus, due to consists mainly of

platelets and a small amount of fibrin or red blood cells. Leukocytes are also actively recruited to platelet-rich arterial thrombi [11].

The differences from a clinical point of view are as follows: (1) hereditary hypercoagulation (occurs in the "thrombophilia" state), characterized by chronic hyperactivation of the coagulation system, this condition mainly associated with venous rather than arterial thrombosis; and (2) anticoagulant agents (e.g., heparin, warfarin) are usually used to prevent venous thrombosis, whereas antiplatelet agents (e.g., aspirin) are used to prevent arterial thrombosis. In both types of thrombus consists of platelets, fibrin, erythrocytes, and leukocytes with different compositions. Moreover, all thrombi are undergoing propagation, organization, embolization, lysis, and thrombosis, and this dynamic remodeling results in a changing composition [11].

#### **3.1 Arterial thromboembolism**

Rudolph Virchow describes three conditions that induce thrombosis, called the Virchow triad. This triad includes endothelial injury, blood flow stasis or turbulence, and blood hypercoagulability. Abnormalities of one or more of these conditions more often manifest the occurrence of DVT. DVT after trauma is more common in conditions of stasis and endothelial injury while spontaneous DVT is more common in cases of hypercoagulability. Risk factors can be classified as acquired or genetic. Genetic risk factors can be divided into strong, moderate, and weak factors. Strong risk factors include deficiency of antithrombin, protein C and protein S. Moderate risk factors include factor V Leiden, prothrombin 20210A, non-O blood type, and fibrinogen 10034C > T. Weak genetic risk factors include fibrinogen variants, factor XIII, and factor XI [11, 12].

Normal wall shear rates range from 300 to 800/s in the large arteries and increase to about 500 to 1600/s in the arterial of microcirculation. However, in pathological stenotic vessels, the wall shear rate can be up to 10,000/s or even higher. The increased shear stress in the microenvironment of the atherosclerotic plaque area of the stenotic vessel is exacerbated by turbulent blood flow. This high hemodynamic force can activate platelets as they pass through the region. This abnormal flow can cause local endothelial dysfunction. High shear stress, especially with a marked shear gradient around the site of the stenosis, is sufficient to induce VWF from endothelial cells and binding of VWF to platelets via glycoprotein Ib-V-IX. This interaction does not occur in normal circulation, result mediating platelet adhesion to the intima surface and triggering platelet thrombus formation [11].

Heterogeneity is seen in the composition of atherothrombotic plaques, even within the same individual. In addition to plaque composition, differences in the basic structural features of the arteries contribute to differences in thrombogenic substrates. For example, the carotid and iliac arteries contain relatively more elastic fibers and proportionately fewer smooth muscle cells than the coronary arteries. Therefore, coronary artery thrombosis usually results in slightly stenotic, lipidrich plaque, whereas carotid artery usually results in severe stenotic and high-risk plaque [11].

#### **3.2 Venous thromboembolism (VTE)**

Venous thrombi are formed mainly from fibrin and red blood cells. Thrombogenic stimulation is caused by (1) stasis of veins, (2) activation of clotting factors, and (3) vascular damage. Anti-thrombogenic properties through mechanisms (1) inactivation of activated coagulation factors by natural inhibitors such as antithrombin and activated protein C, (2) elimination of activated coagulation factors and soluble fibrin

#### *ABO Blood Group and Thromboembolic Diseases DOI: http://dx.doi.org/10.5772/intechopen.102757*

polymer complexes by mononuclear phagocytic cells and liver, and (3) lysis of fibrin by enzymes fibrinolytic from plasma and endothelial cells [11].

In the adult group, the predisposition factors to VTE are increasing age, cancer, prolonged immobilization, stroke or paralysis, varicose veins, prolonged air travel, acute inflammatory bowel disease, rheumatic disease, and nephrotic syndrome, oral contraceptive pills, especially those containing third-generation progestins. In the pediatric group, the risk factors for thromboembolism are central venous lines, cancer, and chemotherapy [13].

Venous thrombi are almost always occlusive and can form casts of the vessels in which they arise. Unlike arterial thrombus, severe vascular damage is generally not found at the site of venous thrombosis. Therefore, in low-flow and low-pressure venous systems, decreased blood flow (stasis) and systemic activation of the coagulation cascade play a major pathophysiological role. Venous thrombi consist mostly of red blood cells trapped in fibrin and contain relatively few platelets; hence, they have been described pathologically as red thrombi [11].

The study of Sun et al. in 1412 patients with VTE (consisting of 600 DVT patients, 441 PE patients, and 371 patients having a diagnosis of DVT and PE) and 199,248 controls the results of VTE patients were significantly higher in the non-O blood group compared to all non-VTE discharge patients with OR 1.362 (95% confidence interval, 1.205-1.540). When the non-O group was classified into A, B, and AB and a pairwise comparison test was performed on VTE and non-VTE patients, the results were not statistically different [14].

## **4. The relation of ABO blood group and thromboembolic diseases**

ABO blood group has been recognized as a risk factor for thromboembolic diseases since the 1960s. Many studies have shown that the non-O group had a higher incidence of ischemic heart disease**.** ABO blood type is important in relation to VWF and FVII levels because in turn confer a clear risk of increased VTE especially in non-O blood groups which provide a higher increase. This association is less clear for CAD and MI but a similar pattern emerges with most studies finding group O to be at lower risk [15].

The Framingham Heart Study, and others, resulted in blood group A having an increased risk of CAD [16–18] and MI [19]. More specifically, blood type A is associated with early detection of CAD [19, 20] and predominates in patients with MI [21]. Another study reported that groups B [22, 23] or AB [24] had a higher incidence of CAD. In contrast, Mitchell [25] reported that cities with a higher prevalence of group O had higher rates of cardiovascular mortality and a study in India showed that blood type O increased the risk of CAD [26]. Further studies did not identify any association between blood type and CAD [27, 28]. Based on these inconsistent results, He et al. [29] conducted a meta-analysis found the highest risk of CAD was observed in blood group AB, followed by groups B, A, and O. This is similar to ABO-associated vWF/FVII levels which the highest in group AB, followed by groups B, A and O [18].

The theory proposed to explain the relationship between ABO blood group and CAD is as follows. Fibrinogen together with vWF activates platelet aggregation and adhesion which in turn plays a role in the development of atherosclerosis. On the other hand, blood group A has been reported to have higher cholesterol levels and lower lipoprotein density, this may explain the association with an increased risk of CAD. In addition, ABO loci have been reported to be associated with inflammatoryforming CAD, including intercellular adhesion molecule-1, soluble P selectin, soluble E selectin, and tumor necrosis factor-α. Meanwhile, the interaction between genetic factors (genes known to increase susceptibility to CAD and the ABO locus) and environmental factors still contribute to the risk of CAD and MI [15].

The incidence of VTE is more often due to factor VIII (FVIII) and von Willebrand Factor (VWF) levels are higher in the non-O blood group than in the O blood group. Moeller et al. comparing VWF and FVII levels in individuals with ABO phenotype found the following order O < A < B < AB for vWF levels and O < A < AB < B for FVII levels [30]. Nevertheless, Simangunsong et al. found no significant differences were present in factor VIII activity between A, B, and O blood types [31].

A blood type that is identical to high vWF, is an important genetic factor that explains around 30% of the variation in factor VIII levels. There is a relationship between factor VIII and vWF. However, attempts to find other genetic loci associated with high vWF and factor VIII levels have not been successful to date. Most likely, the high factor VIII levels are due to increased synthesis or decreased clearance of the vWF-factor VIII complex [32]. Furthermore, non-O blood groups are associated with increased arterial and venous thrombotic events possibly mediated by increased levels of von Willebrand factor and factor VIII in non-O blood groups [33].

Meanwhile, several studies have confirmed that the level of vWF is lower in people who have blood type O, therefore FVIII: C is reduced due to the stabilizing function of vWF as an FVIII: C carrier. Factor VIII affinity for vWF may also differ from individual to individual, which is genetically determined [30].

Blood group A is associated with an increased odds of major adverse cardiovascular events (MACE), whereas blood group O was associated with a reduction in the odds of MACE in patients with COVID19. These findings suggest an association between blood group type and cardiovascular complications in COVID-19. The biological mechanism behind the role of ABO blood groups in COVID-19 remains elusive. Natural anti-glycan ABO antibodies have been shown to inhibit SARS-CoV1 interaction of spike protein and angiotensin-converting enzyme 2 (ACE2) [33].

In the cellular experimental model approach, it can be proven that the binding of the SARS-CoV S protein with ACE2 on target cells can be blocked by anti-A antibodies in the blood group, because the S protein is synthesized by A-antigenexpressing cells, after transfection by cDNA glycosyltransferases. in accordance. When produced in cells expressing blood type A or B enzymes, SARS virions are decorated by appropriate glycan antigens, consequently, the presence of anti-A and anti-B antibodies in blood type O individuals can block the attachment and entry of the virus thereby preventing infection. Therefore, individuals with blood type O will have a lower risk of infection than non-O individuals. This phenomenon occurred during the 2003 Hong Kong SARS hospital outbreak, and a similar trend was recently observed for COVID-19 in China, the infectious SARS virions are decorated by glycan antigens corresponding to blood group A or B, and the presence of anti-A antibodies and anti-B in individuals with blood type O can prevent infection by blocking the attachment and entry of the virus [34, 35].

Vasan study used data on 1.1 million healthy blood donors from the binational database SCANDAT2 (Scandinavian Donations and Transfusions), which contains national data on blood donation and transfusion from Sweden and Denmark, to investigate the association between ABO blood type and arterial thrombotic events. or veins. And the results confirm that there is a consistent relationship between non-O blood type and VTE and cardiovascular events, with a greater risk in the venous. The proposed basic mechanisms driving this association include higher concentrations of factor VIII and von Willebrand factor in individuals with non-O blood types. This study provides strong evidence of a consistent relationship between the non-O blood group and VTE, and the incidence of cardiovascular thrombosis, with a greater risk of recurrence in non-O blood groups. Also, non-O blood groups confer an increased risk of thromboembolism, ABO blood groups may

#### *ABO Blood Group and Thromboembolic Diseases DOI: http://dx.doi.org/10.5772/intechopen.102757*

have a role in thrombosis risk assessment and could potentially be added to existing clinical prediction systems [5].

Sickle cell disease or what is known as sickle cell trait (SCT) in individuals will provide a risk of DVT even though it is weak. This potential risk will increase if the patient has a non-O blood group. This combined effect will increase the activation of clotting factors and increase the risk of DVT. Thus, caution should be exercised in co-inheritance of non-O blood group and SCT, in which case it should be paid attention to assess the risk profile of DVT in patients in Africa and other areas where SCT is common [6].

Non-group O patients have susceptibility and greater risk of VTE than patients of group O and have greater levels of von Willebrand factor (vWF) and factor VIII. The risk of VTE is probably related to the level of vWF and factor VIII. A, B, and H blood group antigens are expressed on N-glycans of VWF and influence the half-life of the protein (10 hours for group O and 25 hours for non-O subjects), explaining the greater levels in non-O patients [8].

In the report of Rejtő et al. who investigated the effect of ABO, VWF level, age on the variability of F VIII levels in 8 patients non-severe Hemophilia A results that ABO and VWF levels did not influence the variability of FVIII levels, whereas age had only a small influenced [36].

The coagulation process is under the control of several inhibitors which limit clot formation. A balance between procoagulants and anticoagulants is necessary for maintaining hemostasis. A thrombus is formed as a result of a disturbance in this balance. Thrombus is formed when the procoagulant activity of one of the coagulation factors is increased or the activity of one of the natural inhibitors is decreased, a condition called thrombophilia can occur in inherited deficiency of natural inhibitors, as well as with inherited gain-of-function mutations of some coagulation factors. The deficiency of natural inhibitors such as antithrombin, protein C and inherited protein S is a strong risk factor for venous thrombosis; they have little or no effect on arterial thrombosis. Antithrombin directly inhibits several activated coagulation factors, notably thrombin, and activated factor X, and the inhibitory effect is amplified by its binding to glycosaminoglycans on the endothelial surface carrying heparin-like activity. The effect of increasing the tendency for clot formation is especially in the venous system where the coagulation pathway (different from that of platelets) plays a major role. The anticoagulant protein C on the surface of the endothelium is very important in the down-regulation of thrombin formation. Activated protein C inactivates factor Va and factor VIIIa proteolytically, the two most important activated cofactors of the coagulation cascade, causing a slowdown in the rates of thrombin and fibrin formation. The inhibitory effect of activated protein C is accelerated by its main cofactor, protein S. Inherited deficiency of one of these inhibitors leads to increased thrombin formation, increasing susceptibility to VTE [37].

Ahmed et al. hypothesized that if Sickle Cell Trait was a risk factor for DVT, individuals with non-O blood group and SCT (Hb AS) would have a higher risk of DVT than those with non-O blood group and normal hemoglobin (Hb AA) phenotype. The results of this study indicate that SCT itself is a weak risk factor for DVT, but would have the potential to increase the risk of DVT in patients with non-O blood groups. Therefore, co-inheritance of SCT and non-O blood groups is an important risk factor for DVT [6].

The study of Vasan et al. results almost in all age groups, the incidence of VTEs and cardiovascular events is higher in non-O than O blood groups. The incidence rate ratio (IRR) was highest for the venous events, with all venous thrombotic events combined for individuals with non-O blood group compared with blood group O having an IRR of 1.80 (95% CI, 1.71–1.88). The risk patterns were similar

for pulmonary embolism and deep vein thrombosis. Among arterial events, IRRs were generally lower with IRRs of 1.10 (95% CI, 1.05–1.14) for myocardial infarction and 1.07 (95% CI, 1.02–1.12) for stroke in individuals in non-O blood groups compared with those in blood group O [5].

## **5. Summary**

ABO blood type is associated with the risk of thromboembolic diseases. Non-O blood type has a greater risk than O blood type. Thromboembolic events occur in both arteries and venous, which are venous more often, one of the causes is FVIII and VWF clearance in non-O blood groups are longer, results found high levels of both in the non-O blood group. While the manifestation of arterial thromboembolism commonly happened in cardiovascular diseases including coronary arterial disease and myocardial infarct.

## **Conflict of interest**

No conflict of interest in this article.

## **Abbreviations**


*ABO Blood Group and Thromboembolic Diseases DOI: http://dx.doi.org/10.5772/intechopen.102757*

## **Author details**

Yetti Hernaningsih Faculty of Medicine Universitas Airlangga, Dr. Soetomo General Academic Hospital, Surabaya, Indonesia

\*Address all correspondence to: yetti-h@fk.unair.ac.id

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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## **Chapter 4**
