**3.7 Aflatoxins and the immune system's relationship**

Reduced vaccination efficacy, evidence of aflatoxins affecting both innate and acquired/adaptive immunity was found to have an increased incidence and severity of infectious infections, as well as prolonged healing times [3]. According to a study, AFB1 immunotoxicity is mediated by AFBO, as well as interchanging with immunocompetent cells throughout the body, altering their fast growth and/or the manufacture of immune reaction mediators, disrupting innate and adaptive immunity. Although these mechanisms were established using animal studies, AFB1's immunotoxicity has also been confirmed in vitro on human cell lines and in case–control studies in heavily exposed areas such as Ghana [3, 49]. In rats, a ten-fold higher dose of 1 mg AFB1/kg bw increased the number of CD8+ (cytotoxic T cells) while not affecting other immunological markers [3]. Other scientific studies, on the other hand, have demonstrated that the immune response can be altered even at low levels of aflatoxins and shorter exposure times. For example, rats were fed a portion of food that contain about 5 to 75 g AFB1/kg bw for five weeks [50], Other research, on the other hand, has demonstrated that the immune response can be altered even at low levels of aflatoxins and shorter exposure intervals. For five weeks, rats were fed a diet with 5 to 75 g AFB1/kg bw [51]. Although the preponderance of evidence suggests that aflatoxins mostly impair immune function, in vitro and in vivo investigations have revealed that they can also dysregulate immune responses through immunostimulatory effects [52].

### **3.8 The link between aflatoxins and innate immunity**

In vivo and in vitro, structurally barriers example: skin and intestinal epithelial cells are damaged, causing the weakened structure–function against microbial and toxin intrusions. The production of intra-epidermal vesicles and squamous cell carcinoma have been connected to contact with the skin of a variety of animals [53]. Pigs fed an aflatoxins-contaminated diet for 28 days exhibited crusting and skin

#### *Aflatoxins: Toxicity, Occurrences and Chronic Exposure DOI: http://dx.doi.org/10.5772/intechopen.105723*

ulceration on their snouts, lips, and buccal commissures (AFB1, AFB2, AFG1, and AFG2) [3]. Aflatoxins have been shown to impair the intestine's mechanical barrier by interrupting cell cycle development or damaging intestinal epithelial cells and the tight junctions that hold them together in scientific review studies. Broilers fed 0.6 mg AFB1/kg food for exactly 3 weeks had their cell growth interrupted at the G2/M phase, leading to a decrease in jejunum height and a decrease in the villus height/crypt ratio, jeopardizing their function as a selective barrier [54]. The mechanical, chemical, and immunological barriers that protect the gut mucosa from external assaults at the molecular level are affected by aflatoxins. The CacO-2 human cell line was treated in vitro with 1–100 M AFB1 for 48 hours, which decreased trans-epithelial electrical resistance (TEER). As a result, paracellular permeability increased and survival decreased [55]. After 48 hours of exposure to varying doses of AFM1, CacO-2 cells' selective permeability was likewise impaired (0.2 to 20 M) [56]. Cell viability, function, or gene expression of cytokines and chemokines in immune cells like monocytes, macrophages, dendritic cells (DC), and natural killer (NK) cells, all of which play important roles in innate immunity has been shown by a certain secondary metabolite (Flavonoids). TLR-2, TLR-4, and TLR-7 transcription are suppressed in broilers exposed to AFB1, showing a suppressive effect on innate immunity. These receptor proteins have a role in sentinel cells like macrophages and dendritic cells recognizing external invaders, which is a crucial step in initiating an immune response [57]. Human monocytes were pre-treated for 24 hours with as little as 0.1 pg. AFB1/mL before being cultured with *Candida albicans* for 30 minutes at 37°C [3]. In addition, the aflatoxins AFB1, AFB2, and/or AFM1 have been shown in other studies to reduce macrophage viability, proliferation, cytotoxicity, and phagocytic activity, as well as the expression of cytokines like TNF-, IL-1, and IL-6, and the inducible nitric oxide synthase (iNOS), which mediate intracellular pathogen killing during phagocytosis [3]. When dairy cow neutrophils were given low doses of AFB1 for 18 hours (0.01, 0.05, and 0.5 ng/mL), their phagocytic and cytotoxic capacities against *Staphylococcus aureus* and *Escherichia coli* were drastically diminished. This was attributed to the reduction of reactive oxygen species (ROS) in neutrophil cytoplasm, which is important for pathogen killing during phagocytosis [58]. In numerous mammals, aflatoxins blocked the complement system, which is a critical component of innate defense that causes the phagocytosis of dangerous microorganisms [3]. Complement activity was observed to be decreased in cattle and poultry fed at varying threshold levels [59]. After ducklings were fed AFB1 at doses of 0.5 or 0.8 mg/kg feed for 40 days, the APCA was activated for the first 15 days, then suppressed for the remaining days of the study. In contrast, the effect of aflatoxins on the complement system appears to be very reliant on the host, as rabbits fed a 24 mg/kg diet for 28 days showed no significant change in serum hemolytic activity (CH50) [3].

#### **3.9 The link between aflatoxins and adaptive immunity**

The decrease of adaptive/acquired immunity that occurs as a result of aflatoxins exposure is well documented, implying that exposed hosts are more susceptible to infectious pathogens and that vaccine protection is reduced or nonexistent [60]. In contrast to a control group fed an aflatoxin-free diet, vaccination failed to protect pigs against *Erysipelothrix rhusiopathiae* when fed AFB1-contaminated feed [3]. Humans and animals have shown reduced lymphocyte fast growth, activation, and/ or function. In adaptive immunity, lymphocytes are the most significant immune cells. Apoptosis was seen in human peripheral blood cells treated at diverse times

with different dosages of AFG1 (3.12–2000 g/L) [61]. In vitro treatment of human lymphocytes with AFB1 at concentrations ranging from 5 to 165 uM increased the frequency of apoptotic and necrotic lymphocytes in a dose-dependent manner, with a considerable increase in cell necrosis beginning at 50 uM (15.6 mg/L) after 24 hours [62]. T-cell proliferation was decreased in a dose-dependent manner starting at 15 M in vitro culture of the human lymphoblastoid Jurkat T-cell line with AFB1 or AFM1 at 3-50 M concentrations range for 72 hours, but no apoptosis or necrosis was seen [63]. When compared to negative control cells cultivated in the absence of aflatoxins, AFB1 and AFM1 dramatically enhanced the expression of IL-8, a cytokine implicated in innate immunity, while adaptive immunity was unaffected, as seen by unchanged levels of interferon (INF)- and IL-2 cytokine [3]. AFB1 and AFM1 significantly increased the expression of IL-8, a cytokine implicated in innate immunity, when compared to negative control cells cultivated in the absence of aflatoxins, while adaptive immunity was unaffected, as seen by unchanged levels of interferon (INF) and IL-2 cytokine [64]. The suppression of adaptive CMI has been researched in lab animals such as chickens and rats, with results showing a decrease in the amount of distinct T-cell lymphocyte subsets as well as the cytokines they release, both of which are important components of this form of the immune response. Reduced delayedtype hypersensitivity (DTH) in a variety of species, including chicken and rats, at doses ranging from 0.3 to 1.0 mg/kg feed, supported adaptive CMI suppression by aflatoxins, meaning a reduction in the frequency of adaptive CMI cases [65]. Rats given AFB1 dosages ranging from 5 to 75 g/kg bw for five weeks had decreased proliferation and cytokine production in splenic helper T cells (CD4+) engaging in acquired cellular immunity. In laboratory animals, adaptive CMI has been studied [50]. AFM1 decreased DTH and related T lymphocyte subsets (CD3+, CD4+, CD8+, CD19+, and CD49 b), as well as the interleukins they release, such as INF-, IL-10, and IL-4, in mice administered 25 or 50 g/kg bw intraperitoneally [49]. A decrease in CD3+ and CD19+ lymphocyte subsets bearing the D69 activation marker (i.e., CD3 + CD69+ and CD19 + CD69+), as well as CD8+ T-cells, which play a key role in vaccination and immune response against pathogens, was highly correlated with high levels of AFB1, as measured by the concentrations of AFB1-albumin adduct in the serum [66].

#### **3.10 Aflatoxins, malnutrition, and neurodegenerative diseases are linked**

Aflatoxins have been linked to a variety of diseases, each with its own set of processes and risk factors. Malnutrition problems include malnutrition (faltering and stunting), physical and mental maturation issues, reproductive and sexuality troubles, and nervous system abnormalities, among others (neurodegenerative diseases and neuroblastoma) [67, 68]. Chronic aflatoxins exposure has been related to neurological illnesses, according to a growing body of scientific evidence. In neuronal brain cells, oxidative stress caused by aflatoxins, as well as AFBO and ROS produced by CYP450 enzymes, react with functional macromolecules, restricting lipid and protein synthesis and causing degeneration [69]. Aflatoxins have also been shown to disrupt the structure and function of mitochondria in brain cells, causing oxidative phosphorylation to be inhibited and cell [70]. As with vitamins A, C, and E, aflatoxin interferes with vitamin and mineral absorption, worsening low nutritional status, and selenium deficiency inhibits children's growth [71]. As a result, children exposed during pregnancy may develop growth abnormalities that remain throughout adulthood, including stunted and delayed physical and mental maturation [72].

#### **3.11 Aflatoxin and kwashiorkor investigations in the past**

A possible link between aflatoxin exposure and childhood kwashiorkor, a disorder characterized by the protein-energy shortage, was debated decades ago. Kwashiorkor and marasmus (another malnutrition-related childhood disease prevalent in impoverished countries) are both severe malnutrition diseases. Although protein deficiency is a fundamental cause of both kwashiorkor and marasmus, one key difference between the two conditions is that kwashiorkor can occur even when the children's calorie intake is adequate, whereas marasmus can only be caused by low caloric intake [73]. Fatty liver and edema, both frequent kwashiorkor signs, are less likely in children with marasmus. Kwashiorkor's symptoms include anorexia and light-colored hair and skin [74]. Marasmic kwashiorkor is defined as edema from kwashiorkor combined with wasting from marasmus [75]. According to a scientific study, children with kwashiorkor had higher amounts of aflatoxins or their metabolites in their blood or urine than children with other protein malnutrition-related illnesses such as marasmus. Furthermore, aflatoxins were identified in autopsies of children who died from kwashiorkor in their lungs and livers, but not in their kidneys, but not at statistically significant levels, compared to those who died from other diseases or other forms of malnutrition [76]. Kwashiorkor patients were paired with children who did not show any indications or symptoms of protein-energy deficit. All of the children's serum and/or urine contained aflatoxins. Although the controls had a higher proportion of urine aflatoxins than the kwashiorkor group, the kwashiorkor group had a much higher serum/urine ratio. Rather than aflatoxin playing a direct role in the production of kwashiorkor, these data could imply that kwashiorkor has decreased liver function, which could lead to abnormalities in aflatoxin metabolism. Indeed, it has been proposed that children with kwashiorkor are more susceptible to the hazards of Aflatoxin in the diet [74].

#### **4. Conclusions**

Aflatoxins being very common and highly toxic, pose a great threat to food safety, more research would aid in a better understanding of their toxicity incidence, patterns, and resultant correlations with foods and other illnesses to appropriately address their negative effects on public health and the economy. With the growing prevalence of aflatoxin in developing countries where agroclimatic zones encourage aflatoxin growth in cash crops such as peanut, maize, sorghum, and sunflower; contamination of farm produce in endemic regions continues to be a major impediment to international trade and food security, as it not only affects local populations but also has the potential to spread to other parts of the world by either exporting highly contaminated goods or restricting their marketability, both of which contribute to rising prices and limiting access. Interventions can be made to target the inhibitions of these fungi on the field and in their storage produce if the mechanism of actions is well understood. The data presented through this research aims to delve more into the growing body of evidence associating teratogenicity, immunotoxicity, malnutrition ('kwashiorkor'), neurological disease, and aflatoxin exposure with respect to cancers. More research is needed to determine the mechanism that connects aflatoxins to the many diseases they cause. The link between Aflatoxin exposure and the immune system reveals that this fugal's effect is lethal and should be handled with prudence. Furthermore, studies show that aflatoxins impair immune function in humans who are exposed to these natural fungal toxins.
