**2.2 Food allergens**

218 Atopic Dermatitis – Disease Etiology and Clinical Management

improvement in clinical symptoms although not complete remission. AD patients not sensitized or not exposed to mites benefited as much from exposure to mite free

Many AD patients are highly sensitized to aeroallergens and experience precipitation of AD upon epicutaneous or bronchial allergen exposure. RAST and SPT help to verify or exclude the presence of IgE mediated hypersensitivity, by measurement of allergen specific IgE in serum and evaluation of IgE bound on mast cells. Neither test procedure considers those AD patients characterized by cell-mediated sensitization. The APT was established as a provocation test for a subgroup of AD patients to study the induction of eczema by aeroallergens after 24-72 hours. It is similar to nasal or bronchial provocation test in allergic rhinitis and asthma. Allergen specific IgE is not obligatory for a positive APT reaction. APT has shown a higher specificity towards inhalants (69-92%) when compared to SPT (44-53%) and serum specific IgE (42-64%), suggesting a more appropriate screening role for SPT and RAST in this context. APT does not replace the classical methods of diagnosis of IgEmediated allergy. APT are usually negative in individuals with respiratory allergy and healthy subjects pointing to AD specific triggering mechanisms required to produce APT positivity. Much effort has been undertaken to standardize APT procedures. The protocol of the European task Force on Atopic Dermatitis (ETFAD) provides a standardized APT

Despite above impressive data on APT as a diagnostic tool, final scientific proof for the relevance of aeroallergens as identified by positive APT, for clinical manifestation of AD is still missing. The question on how well APT can identify AD patients who would benefit

• Suspicion of aeroallergen symptoms without proof of positive specific IgE or positive

• Multiple IgE sensitizations without proven clinical relevance in patients with eczema

In summary sensitization to inhalant allergens is a major contributing factor to the pathogenesis and perpetuation of AD. It is found more commonly in older children and later life of AD individuals and is demonstrated by presence of aeroallergen specific IgE and positive SPT to aeroallergens. Bronchial inhalation challenge, RAST, SPT, and APT to

environment as those with mite sensitization and/or exposure.

• Evidence of aeroallergen specific T cells invading the skin

• Exacerbation of AD following epicutaneous aeroallergen application

Table 3. Factors implicating aeroallergens underlying pathomechanism of AD

• Exacerbation of AD following exposure to aeroallergen

• Clinical improvement in aeroallergen poor environment

• Presence of aeroallergen specific IgE

• New skin lesions induced by APT

technique (Ronchetti et al., 2008).

SPT

from allergen avoidance remains to be answered.

Table 4. ETFAD consensus on APT indications

• Severe and/or persistent AD with unknown trigger factors

The prevalence of AD and food allergies (FA) appears to have increased in recent years in many western countries. In this context it is important to define the terms. FA and food hypersensitivity (FH) indicate an adverse clinical reaction to food due to interaction of food proteins with one or more immune mechanisms. Food intolerance (FI) is the result of nonimmunological reactions to foods and food additives (Reitamo et al., 2008).


Table 5. Types of adverse reactions to foods

FA has the greatest incidence in infancy and early childhood. Around 8% of children are thought to develop adverse reactions to food, most of them within the first year of life. The prevalence of FA varies between regions and is influenced by culture and genetic factors. The spectrum of food allergens has remained relatively unchanged despite the rise of FA incidence. Seven food items account for 90% of FA in children. These include cow's milk, egg, peanuts, soybeans, wheat, fish, and tree nuts. By three years of age the majority of children will have developed tolerance to these food items with the exception of peanuts/ tree nuts and seafood. In adults, IgE mediated FA is rare. The main food allergens in adults are peanuts, tree nuts, fish and shellfish (Kim, 2008).


Table 6. Major food allergens in children and adults

In general high-protein food allergens are considered to be more allergenic. Most food allergens are water-soluble glycoproteins that are particularly resistant to food processing, cooking and digestion.

Trigger Factors, Allergens and Allergy Testing in Atopic Dermatitis 221

• Symptoms can involve more than one organ (oral itching and/or swelling, nausea, vomiting, abdominal pain, diarrhea, asthma, rhinitis, urticaria, angioedema,

FA is the earliest manifestation of atopy affecting both breast- and formula-fed infants. Early sensitization to food allergens is typically transient. It affects AD individuals mainly in the first 2 to 3 years but particularly in the first 12 months of life and is often followed by inhalant sensitization as demonstrated by presence of aeroallergen specific IgE and positive SPT to aeroallergens. These may in turn contribute to ongoing eczema later in life (older children and adults). Multiple studies have established that approximately 35% of children with moderate to severe AD have FA. Double-blind placebo-controlled food challenge (DBPCFC) is the gold standard for diagnosis of FA. Children with AD, that were assessed for FA by DBPCFC showed reactions in 40% of challenges. Of the positive challenges skin symptoms occurred in 84% of AD subjects, 56% showed either skin, GIT or respiratory symptoms and only 30% developed isolated skin reactions. Children with positive DBPCFC were younger than those without. Generally, the younger the patient and the more severe the AD, the more likely FA is to be a causative factor (Reitamo et al., 2008 & Kim, 2008). In adults with AD IgE-mediated FA plays only a minor role (1-3%). In this group birch pollen related food allergens have been shown to be a major predisposing factor. In recent years pseudo allergens have been reported to exacerbate symptoms in adults with AD, although it is still controversial if these observations always reflect a true pseudo allergic underlying pathomechanism. Pseudo allergic reactions are more known in the clinical context of urticaria and angioedema. To date no reliable laboratory or skin tests are available to diagnose pseudo allergy, so that for the identification of possible pseudo allergen trigger

• Specific food antigen can be identified

anaphylaxis)

• Timing of symptoms closely related to food intake

• Positive personal or family history of other atopic disorders

factors elimination diet and oral challenge are the norm (Reese et al., 2009).

positive results (Robinson & Smart, 2008 & Goodwin, 2008 & Kim, 2008).

Approximately 85% of AD individuals have specific IgE to food- and aeroallergens, making diagnosis of FA based on laboratory testing alone inadvisable. The importance of a careful history cannot be overemphasized. The history combined with diagnostic tests, should point toward a few possible offending foods or groups of food products. Food allergen specific IgE is a useful tool in the assessment of FA. A different positive predictive cut off point exists for each allergen tested and similar test results do not imply a similar clinical reaction to different allergen. Higher levels of specific IgE indicate increased likelihood of allergic reaction with exposure. Levels though cannot predict the severity of allergic reaction. In general positive RAST results only indicate the presence of IgE to an allergen or crossreacting allergen and may not correlate with true clinical reactions. Patients with AD can have very high levels of non-specific IgE, which can be detected and give rise to false

SPT in the diagnosis of FA in infancy is thought to be unreliable. It can provide rapid results with high sensitivity, and has a high negative predictive value (>95%), with a negative skin test essentially excluding IgE- mediated FA. In contrast the positive predictive value is

Table 8. Factors suggesting classic IgE mediated food allergy


Table 7. Common food allergens

FA in infancy is thought to be due to a failure of the gastrointestinal tract (GIT) to develop oral tolerance (OT). No down regulation occurs of GIT immune system in its responsiveness towards ingested soluble food antigens. Factors predisposing to impaired OT include increased antigen uptake, decreased production of secretory IgA, and an imbalance towards Th2 response. Other factors include dose and frequency of antigen exposure, biological characteristics of antigens as well as early intestinal inflammation affecting gut permeability and mucosal antigen uptake. IgE sensitization can occur as early as during fetal period and maternally ingested antigens can be excreted in the breast milk. An additional mode of sensitization to food allergens in AD individuals may involve the impaired skin barrier function, so that sensitization to food allergens may occur even though the food in question has not yet been integrated into the diet (Reitamo et al., 2008 & Kim, 2008).

Immunologically triggered FA can clinically present as immediate (oral allergy syndrome, urticaria, angioedema, bronchospasm and anaphylaxis), intermediate (predominantly GIT symptoms), and late-onset reactions (AD flares, development of cough and wheeze).

• Specific food antigen can be identified

220 Atopic Dermatitis – Disease Etiology and Clinical Management

*Caseins* α1-casein α2-casein β-casein κ-casein γ-casein

*Whey proteins*  β-lactoglobulin α-lactalbumin Bovine serum albumin (BSA)

Ovomucoid Ovalbumin Ovotransferrin/conalbumin Lysozyme

> Vicillin Conglutin Glycinin

Gly m 1 Trypsin inhibitor

FA in infancy is thought to be due to a failure of the gastrointestinal tract (GIT) to develop oral tolerance (OT). No down regulation occurs of GIT immune system in its responsiveness towards ingested soluble food antigens. Factors predisposing to impaired OT include increased antigen uptake, decreased production of secretory IgA, and an imbalance towards Th2 response. Other factors include dose and frequency of antigen exposure, biological characteristics of antigens as well as early intestinal inflammation affecting gut permeability and mucosal antigen uptake. IgE sensitization can occur as early as during fetal period and maternally ingested antigens can be excreted in the breast milk. An additional mode of sensitization to food allergens in AD individuals may involve the impaired skin barrier function, so that sensitization to food allergens may occur even though the food in question has not yet been integrated into the diet (Reitamo

Immunologically triggered FA can clinically present as immediate (oral allergy syndrome, urticaria, angioedema, bronchospasm and anaphylaxis), intermediate (predominantly GIT

symptoms), and late-onset reactions (AD flares, development of cough and wheeze).

**Food Item Protein** 

Cow's milk

Egg white

Peanut

Soy bean

Table 7. Common food allergens

et al., 2008 & Kim, 2008).


Table 8. Factors suggesting classic IgE mediated food allergy

FA is the earliest manifestation of atopy affecting both breast- and formula-fed infants. Early sensitization to food allergens is typically transient. It affects AD individuals mainly in the first 2 to 3 years but particularly in the first 12 months of life and is often followed by inhalant sensitization as demonstrated by presence of aeroallergen specific IgE and positive SPT to aeroallergens. These may in turn contribute to ongoing eczema later in life (older children and adults). Multiple studies have established that approximately 35% of children with moderate to severe AD have FA. Double-blind placebo-controlled food challenge (DBPCFC) is the gold standard for diagnosis of FA. Children with AD, that were assessed for FA by DBPCFC showed reactions in 40% of challenges. Of the positive challenges skin symptoms occurred in 84% of AD subjects, 56% showed either skin, GIT or respiratory symptoms and only 30% developed isolated skin reactions. Children with positive DBPCFC were younger than those without. Generally, the younger the patient and the more severe the AD, the more likely FA is to be a causative factor (Reitamo et al., 2008 & Kim, 2008). In adults with AD IgE-mediated FA plays only a minor role (1-3%). In this group birch pollen related food allergens have been shown to be a major predisposing factor. In recent years pseudo allergens have been reported to exacerbate symptoms in adults with AD, although it is still controversial if these observations always reflect a true pseudo allergic underlying pathomechanism. Pseudo allergic reactions are more known in the clinical context of urticaria and angioedema. To date no reliable laboratory or skin tests are available to diagnose pseudo allergy, so that for the identification of possible pseudo allergen trigger factors elimination diet and oral challenge are the norm (Reese et al., 2009).

Approximately 85% of AD individuals have specific IgE to food- and aeroallergens, making diagnosis of FA based on laboratory testing alone inadvisable. The importance of a careful history cannot be overemphasized. The history combined with diagnostic tests, should point toward a few possible offending foods or groups of food products. Food allergen specific IgE is a useful tool in the assessment of FA. A different positive predictive cut off point exists for each allergen tested and similar test results do not imply a similar clinical reaction to different allergen. Higher levels of specific IgE indicate increased likelihood of allergic reaction with exposure. Levels though cannot predict the severity of allergic reaction. In general positive RAST results only indicate the presence of IgE to an allergen or crossreacting allergen and may not correlate with true clinical reactions. Patients with AD can have very high levels of non-specific IgE, which can be detected and give rise to false positive results (Robinson & Smart, 2008 & Goodwin, 2008 & Kim, 2008).

SPT in the diagnosis of FA in infancy is thought to be unreliable. It can provide rapid results with high sensitivity, and has a high negative predictive value (>95%), with a negative skin test essentially excluding IgE- mediated FA. In contrast the positive predictive value is

Trigger Factors, Allergens and Allergy Testing in Atopic Dermatitis 223

The factors influencing colonization and infection of *S. aureus* in AD skin are not yet well understood and likely to be multifactorial. Defective skin barrier function, reduced content of skin lipids, loss of certain innate antibacterial activities via changes of antibacterial peptides on skin, and a more alkaline pH of skin surface are all thought to play a role in this context. Antimicrobial peptides such as β-defensins and cathelicidins are critical elements of the skin's innate immunity. These peptides eliminate not only *S. aureus*, but also fungal, viral and other bacterial pathogens. The decreased antimicrobial peptide levels in AD skin are not caused by intrinsic defect in keratinocyte production but rather to inhibition mediated by the Th2 cytokine milieu in the AD microenvironment (Schlievert et al., 2008). Scratching disturbs the epidermal barrier and releases pro-inflammatory cytokines that up regulate the extracellular matrix molecules to act as adhesins to *S. aureus.* Cracks in the skin expose underlying extracellular matrix molecules to *S. aureus* attachment (Reitamo et al., 2008).

• Increased adherence of *S. aureus* to skin due to raised fibronectin and fibrinogen (so

• Reduced keratinocyte production of β-defensins and LL-37 (antimicrobial peptides)

Staphylococcal super antigens include staphylococcal enterotoxins, classically the common cause of food poisoning and non menstrual toxic shock syndrome (TSS), and TSS toxin1 (TSST-1), the cause of both menstrual and non menstrual TSS. Staphylococcal enterotoxin serotypes A-E (SEA-SEE) and SEG-SEQ are well documented in the literature. Super antigens are defined by their ability to stimulate cytokine release from both T cells and macrophages. They bind directly without antigen processing to constitutively expressed HLD-DR molecules on professional antigen-presenting cells precipitating marked T cell

Most AD individuals show raised specific IgE levels in serum against staphylococcal superantigens and rarely make IgE against constituents of *S. aureus* cell wall. They also demonstrate super antigen specific IgE on their skin. Basophils from patients with superantigen specific IgE release histamine on exposure to relevant superantigen, but not when exposed to super antigens they are not sensitized to. A correlation between presence of superantigen specific IgE and clinical AD severity has been identified and colonization with superantigen producing *S. aureus* is greatest with IgE to staphylococcal superantigen. Skin homing peripheral T cells have also been shown to respond to superantigen and contribute to eosinophilia and IgE production in AD. Epicutaneous application of SEB to unaffected AD skin is followed by exacerbation of eczema suggesting that superantigens can precipitate and sustain the dermal inflammatory cascade in AD individuals. Combined treatment of AD with antibiotics and corticosteroids is more effective than corticosteroid treatment alone suggesting that *S. aureus* secrets products that can induce steroid resistance (Schlievert et al., 2008). In a recent study *S. aureus* strains isolated from steroid resistant AD showed an ability to

Table 9. Factors influencing colonization and infection with *S. aureus* in AD

• Disturbed skin barrier and function • Reduced content of skin lipids • pH of skin surface more alkaline

called adhesins)

stimulation (Macias et al., 2011).

<50%; suggesting that an isolated positive SPT cannot be predictive for FA. A cut off weal diameter of 6-8mm has been demonstrated to be associated with a positive oral food challenge (predictive value >95%). In this context SPT can reduce the need for oral food challenges by 23% when compared to RAST testing. SPT with fresh fruits and vegetables is a better predictor of clinical relevant reaction in comparison to the use of commercial extracts for SPT (Robinson & Smart, 2008 & Goodwin, 2008 & Kim, 2008).

FA in children with AD is thought to be an IgE- and T-cell mediated phenomenon, making the use of the APT a useful diagnostic tool. Clinical studies have demonstrated the APT to be particularly useful in predicting late-phase clinical reactions. However different studies have published contradicting results regarding sensitivity of unstandardized food APT and further clinical studies are required for standardization and patient group selection for food APT. APT cannot replace oral food challenges. Finally APT in conjunction with positive RAST and positive SPT to food allergens has been shown to reliably predict positive food challenges (Robinson & Smart, 2008 & Goodwin, 2008 & Kim, 2008 & Ronchetti et al., 2008).

In summary, a proper dietary and clinical history combined with available testing are more likely to yield a clinical relevant result. Involvement of a dietitian is paramount in AD patients complaining of FA in order to avoid malnutrition in the long run.

#### **2.3 Microbial allergens**

Interaction with environmental microbes may be important in the causation of AD in a number of ways. Early-life exposure may condition maturation of the immune system so that apparent dysregulation associated with IgE production and allergy formation does not occur. The possible role of microbes in the early maturation of the immune system may be the major factor that could explain the differences between western and developing world regarding the incidence of atopy and allergic diseases. Microbes entering via fecal-oral route have been shown to have a greater protective effect against development of allergic diseases than those entering via respiratory route. Early exposure to Hepatitis A virus, *Helicobacter pylori* or *Toxoplasma gondii* has been associated with a reduced risk for atopy by 60%. The burden of exposure of microbial endotoxins in early infancy is thought to play a major role in driving the immune system towards protective responses and away from nuisance responses that are associated with allergy (Burns et al., 2004). A number of observations suggest the relevance of skin flora in clinical manifestation of AD. In individuals with atopic phenotype, eczema may be induced or exacerbated by staphylococcal toxins or by the presence of *Malassezia* yeasts on the skin.

*Staphylococcus aureus* is found on the skin of 90% of chronic AD individuals, but only on 5% of healthy subjects. When present on healthy normal skin *S. aureus* is usually low in number and mainly confined to intertriginous areas and nasal nares. The presence of *S. aureus* on atopic skin depends on the skin lesion. *S. aureus* has been isolated in 55-75% of clinically unaffected AD skin, 85-91% of chronic lichenified lesions and 80-100% of acute exsudative eczematous lesions. The density of *S. aureus* on acutely inflamed AD skin can be 1000-fold higher than on uninvolved skin in AD individuals suggesting a good correlation between the degree of bacterial colonization and clinical disease severity

The ability of *S. aureus* to cause human disease is dependent on production of cell surface adhesions, antiphagocytic factors and secreted exotoxins, whose function appear to be both securing nutrient for microbes and delaying function of immune system. Among the factors secreted by *S. aureus* is the large family of superantigen exotoxins.

The factors influencing colonization and infection of *S. aureus* in AD skin are not yet well understood and likely to be multifactorial. Defective skin barrier function, reduced content of skin lipids, loss of certain innate antibacterial activities via changes of antibacterial peptides on skin, and a more alkaline pH of skin surface are all thought to play a role in this context. Antimicrobial peptides such as β-defensins and cathelicidins are critical elements of the skin's innate immunity. These peptides eliminate not only *S. aureus*, but also fungal, viral and other bacterial pathogens. The decreased antimicrobial peptide levels in AD skin are not caused by intrinsic defect in keratinocyte production but rather to inhibition mediated by the Th2 cytokine milieu in the AD microenvironment (Schlievert et al., 2008). Scratching disturbs the epidermal barrier and releases pro-inflammatory cytokines that up regulate the extracellular matrix molecules to act as adhesins to *S. aureus.* Cracks in the skin expose underlying extracellular matrix molecules to *S. aureus* attachment (Reitamo et al., 2008).


222 Atopic Dermatitis – Disease Etiology and Clinical Management

<50%; suggesting that an isolated positive SPT cannot be predictive for FA. A cut off weal diameter of 6-8mm has been demonstrated to be associated with a positive oral food challenge (predictive value >95%). In this context SPT can reduce the need for oral food challenges by 23% when compared to RAST testing. SPT with fresh fruits and vegetables is a better predictor of clinical relevant reaction in comparison to the use of commercial extracts

FA in children with AD is thought to be an IgE- and T-cell mediated phenomenon, making the use of the APT a useful diagnostic tool. Clinical studies have demonstrated the APT to be particularly useful in predicting late-phase clinical reactions. However different studies have published contradicting results regarding sensitivity of unstandardized food APT and further clinical studies are required for standardization and patient group selection for food APT. APT cannot replace oral food challenges. Finally APT in conjunction with positive RAST and positive SPT to food allergens has been shown to reliably predict positive food challenges (Robinson & Smart, 2008 & Goodwin, 2008 & Kim, 2008 & Ronchetti et al., 2008). In summary, a proper dietary and clinical history combined with available testing are more likely to yield a clinical relevant result. Involvement of a dietitian is paramount in AD

Interaction with environmental microbes may be important in the causation of AD in a number of ways. Early-life exposure may condition maturation of the immune system so that apparent dysregulation associated with IgE production and allergy formation does not occur. The possible role of microbes in the early maturation of the immune system may be the major factor that could explain the differences between western and developing world regarding the incidence of atopy and allergic diseases. Microbes entering via fecal-oral route have been shown to have a greater protective effect against development of allergic diseases than those entering via respiratory route. Early exposure to Hepatitis A virus, *Helicobacter pylori* or *Toxoplasma gondii* has been associated with a reduced risk for atopy by 60%. The burden of exposure of microbial endotoxins in early infancy is thought to play a major role in driving the immune system towards protective responses and away from nuisance responses that are associated with allergy (Burns et al., 2004). A number of observations suggest the relevance of skin flora in clinical manifestation of AD. In individuals with atopic phenotype, eczema may be induced or exacerbated by staphylococcal toxins or by the

*Staphylococcus aureus* is found on the skin of 90% of chronic AD individuals, but only on 5% of healthy subjects. When present on healthy normal skin *S. aureus* is usually low in number and mainly confined to intertriginous areas and nasal nares. The presence of *S. aureus* on atopic skin depends on the skin lesion. *S. aureus* has been isolated in 55-75% of clinically unaffected AD skin, 85-91% of chronic lichenified lesions and 80-100% of acute exsudative eczematous lesions. The density of *S. aureus* on acutely inflamed AD skin can be 1000-fold higher than on uninvolved skin in AD individuals suggesting a good correlation between

The ability of *S. aureus* to cause human disease is dependent on production of cell surface adhesions, antiphagocytic factors and secreted exotoxins, whose function appear to be both securing nutrient for microbes and delaying function of immune system. Among the factors

for SPT (Robinson & Smart, 2008 & Goodwin, 2008 & Kim, 2008).

patients complaining of FA in order to avoid malnutrition in the long run.

**2.3 Microbial allergens** 

presence of *Malassezia* yeasts on the skin.

the degree of bacterial colonization and clinical disease severity

secreted by *S. aureus* is the large family of superantigen exotoxins.


#### Table 9. Factors influencing colonization and infection with *S. aureus* in AD

Staphylococcal super antigens include staphylococcal enterotoxins, classically the common cause of food poisoning and non menstrual toxic shock syndrome (TSS), and TSS toxin1 (TSST-1), the cause of both menstrual and non menstrual TSS. Staphylococcal enterotoxin serotypes A-E (SEA-SEE) and SEG-SEQ are well documented in the literature. Super antigens are defined by their ability to stimulate cytokine release from both T cells and macrophages. They bind directly without antigen processing to constitutively expressed HLD-DR molecules on professional antigen-presenting cells precipitating marked T cell stimulation (Macias et al., 2011).

Most AD individuals show raised specific IgE levels in serum against staphylococcal superantigens and rarely make IgE against constituents of *S. aureus* cell wall. They also demonstrate super antigen specific IgE on their skin. Basophils from patients with superantigen specific IgE release histamine on exposure to relevant superantigen, but not when exposed to super antigens they are not sensitized to. A correlation between presence of superantigen specific IgE and clinical AD severity has been identified and colonization with superantigen producing *S. aureus* is greatest with IgE to staphylococcal superantigen. Skin homing peripheral T cells have also been shown to respond to superantigen and contribute to eosinophilia and IgE production in AD. Epicutaneous application of SEB to unaffected AD skin is followed by exacerbation of eczema suggesting that superantigens can precipitate and sustain the dermal inflammatory cascade in AD individuals. Combined treatment of AD with antibiotics and corticosteroids is more effective than corticosteroid treatment alone suggesting that *S. aureus* secrets products that can induce steroid resistance (Schlievert et al., 2008). In a recent study *S. aureus* strains isolated from steroid resistant AD showed an ability to

Trigger Factors, Allergens and Allergy Testing in Atopic Dermatitis 225

properties. Despite the available positive data on *Malassezia* species and AD there is not convincing proof for the importance of this yeast in AD pathogenesis. *Malassezia* sensitization has been reported in both types of AD, extrinsic and intrinsic, and skin barrier dysfunction in AD enabling easier access and therefore cross reactivity between human and fungal manganese superoxide dismutase might be another explanation for the sensitization

Colonization with *Candida albicans* has been found in higher numbers on involved and uninvolved skin of AD individuals than on normal subjects. More importantly colonization of the gastrointestinal tract with *Candida* yeasts was identified in 70% of AD patients compared to 54% of healthy volunteers. 22-94% of AD individuals have shown positive SPT to *C. albicans* and positive correlation existed between the number of positive SPTs and clinical disease severity. *C. albicans* specific IgE has been reported in 25-88% of AD patients and cross reactivity to *Malassezia* has been described. Interestingly PT with *C. albicans* extracts have shown fewer positive results than the healthy controls. In summary the evidence on *C. albicans* is too small to allow any conclusions about its role in AD

IgE autoreactivity has been implicated in the immune pathogenesis and in particular perpetuation of AD. Striking similarities between environmental allergens and human proteins have been identified on molecular analysis of allergens, and IgE-reactive autoantigens against human proteins have been cloned from human epithelial copy DNA expression libraries. Autoantigens have been detected in IgE-mediated immune complexes in serum of AD individuals and release of autoallergens following tissue (skin barrier) damage has been reported. More importantly reduced levels of IgE autoallergen levels have been noted following successful treatment of AD. It is possible that following initiation of the AD immune and inflammatory cascade in skin and peripheral blood by environmental allergens, these mechanisms are then partially perpetuated by autoallergens. More studies

It is clear that AD individuals are at greater risk in developing irritant contact dermatitis than non-atopic subjects, as contact allergens are likely to penetrate the defective skin barrier more easily. In this context hand eczema has been reported to occur in higher frequency in AD patients. AD individuals, who are particularly employed in occupations involving wetwork are prone to develop an intractable hand dermatitis in their occupational setting leading to considerable occupational disability. Urticaria is frequently encountered in AD individuals, and an allergic basis is found more often in atopic subjects than in the normal population. Contact urticaria of hands may lead to exacerbation of clinical disease in AD particularly in food handlers and slaughterhouse workers (food allergens) as well as

There has been dispute about whether atopic individuals are at greater risk to developing contact allergic reactions. CAD has a reported prevalence of as high as 28% in certain European countries, and similarity in clinical symptoms between AD and CAD makes correct diagnosis of CAD a challenge and can easily lead to misdiagnosis. A recent PT study found that a family history of AD (85%), female sex (74%), and age 11-16 (63%) were

are required in the future to allow any sensible conclusion (Reitamo et al., 2008).

health care workers (latex protein sensitivity) (Burns et al., 2004).

to *Malassezia* yeasts seen in AD.

pathogenesis (Reitamo et al., 2008).

**2.4 Autoallergens** 

**2.5 Contact allergens** 

produce larger numbers of superantigen types per organism. There was also dysregulated production of super antigens and production of unusual superantigen combinations. Reduction of *S. aureus* on AD skin controls the skin inflammation which predisposes to *S. aureus* colonization and/or infection. Discrepancies in antibiotic sensitivity pattern have been documented among *S. aureus* strains colonizing different sites of AD skin (affected and unaffected) and also in AD individuals with prior antibiotic therapy. Repeat microbial susceptibility testing on different body sites is therefore recommended (Kedzierska et al., 2008).


Table 10. Relevance of skin flora for AD

In recent years there is an increasing body of evidence suggesting that yeasts particularly of the genera of *Malassezia* and *Candida* can be relevant for AD pathogenesis. Many studies have demonstrated colonization of AD skin with *Malassezia* yeasts with subsequent deterioration of clinical disease (Darabi et al., 2009). *Malassezia* yeasts are members of the normal human skin flora, and often associated with different dermatological disease. The concentration of yeasts on skin does not have to be raised in AD individuals, suggesting that skin barrier dysfunction and typical changes in skin inflammatory response in AD play a major role. Great variation in density and presence of *Malassezia* yeasts in different sites of AD skin has been documented with the highest concentrations affecting the scalp and upper trunk and the lowest on hands. Sensitization to *Malassezia* yeasts have been exclusively demonstrated in AD individuals, via SPT with *Malassezia* extracts and the presence of *Malassezia* specific IgE antibodies. The density of the yeasts reduces with progressing age, although the yeast cells are larger in adults than in children. *Malassezia* specific IgE in serum has been identified in 20-100% of AD subjects depending on trial. Prevalence was highest in adults with head and neck AD (HNAD) and lowest in children with AD. A strong correlation between *Malassezia* specific IgE levels and severity of HNAD has been found, with *Malassezia* specific IgE being a good marker for HNAD (Darabi et al., 2009). Positive SPT to *Malassezia* extracts have been reported in 13.5-79% of AD individuals, compared to small minority in individuals with other *Malassezia* induced skin conditions. This suggests an exclusive presence of *Malassezia* sensitization in AD subjects. *Malassezia* antigens have been used to APT in some trials and positive results were observed in AD patients suggesting a possible role of *Malassezia* yeasts in eliciting and perpetuating eczema in already sensitized AD individuals (Reitamo et al., 2008 & Darabi et al., 2009). *Malassezia* extracts are not yet part of the standardized APT panel provided by ETFAD. No consistent correlation has been shown between HNAD and positive APT. In many trials oral antifungal therapy has been shown to improve clinical manifestations of AD, particularly in the context of HNAD, exacerbations during adolescence and young childhood, severe AD recalcitrant to conventional therapy, and presence of other atopic diseases. It is not clear yet if this is due to the anti-inflammatory effects of antifungals or due to their antifungal properties. Despite the available positive data on *Malassezia* species and AD there is not convincing proof for the importance of this yeast in AD pathogenesis. *Malassezia* sensitization has been reported in both types of AD, extrinsic and intrinsic, and skin barrier dysfunction in AD enabling easier access and therefore cross reactivity between human and fungal manganese superoxide dismutase might be another explanation for the sensitization to *Malassezia* yeasts seen in AD.

Colonization with *Candida albicans* has been found in higher numbers on involved and uninvolved skin of AD individuals than on normal subjects. More importantly colonization of the gastrointestinal tract with *Candida* yeasts was identified in 70% of AD patients compared to 54% of healthy volunteers. 22-94% of AD individuals have shown positive SPT to *C. albicans* and positive correlation existed between the number of positive SPTs and clinical disease severity. *C. albicans* specific IgE has been reported in 25-88% of AD patients and cross reactivity to *Malassezia* has been described. Interestingly PT with *C. albicans* extracts have shown fewer positive results than the healthy controls. In summary the evidence on *C. albicans* is too small to allow any conclusions about its role in AD pathogenesis (Reitamo et al., 2008).

#### **2.4 Autoallergens**

224 Atopic Dermatitis – Disease Etiology and Clinical Management

produce larger numbers of superantigen types per organism. There was also dysregulated production of super antigens and production of unusual superantigen combinations. Reduction of *S. aureus* on AD skin controls the skin inflammation which predisposes to *S. aureus* colonization and/or infection. Discrepancies in antibiotic sensitivity pattern have been documented among *S. aureus* strains colonizing different sites of AD skin (affected and unaffected) and also in AD individuals with prior antibiotic therapy. Repeat microbial susceptibility testing on different body sites is therefore recommended

In recent years there is an increasing body of evidence suggesting that yeasts particularly of the genera of *Malassezia* and *Candida* can be relevant for AD pathogenesis. Many studies have demonstrated colonization of AD skin with *Malassezia* yeasts with subsequent deterioration of clinical disease (Darabi et al., 2009). *Malassezia* yeasts are members of the normal human skin flora, and often associated with different dermatological disease. The concentration of yeasts on skin does not have to be raised in AD individuals, suggesting that skin barrier dysfunction and typical changes in skin inflammatory response in AD play a major role. Great variation in density and presence of *Malassezia* yeasts in different sites of AD skin has been documented with the highest concentrations affecting the scalp and upper trunk and the lowest on hands. Sensitization to *Malassezia* yeasts have been exclusively demonstrated in AD individuals, via SPT with *Malassezia* extracts and the presence of *Malassezia* specific IgE antibodies. The density of the yeasts reduces with progressing age, although the yeast cells are larger in adults than in children. *Malassezia* specific IgE in serum has been identified in 20-100% of AD subjects depending on trial. Prevalence was highest in adults with head and neck AD (HNAD) and lowest in children with AD. A strong correlation between *Malassezia* specific IgE levels and severity of HNAD has been found, with *Malassezia* specific IgE being a good marker for HNAD (Darabi et al., 2009). Positive SPT to *Malassezia* extracts have been reported in 13.5-79% of AD individuals, compared to small minority in individuals with other *Malassezia* induced skin conditions. This suggests an exclusive presence of *Malassezia* sensitization in AD subjects. *Malassezia* antigens have been used to APT in some trials and positive results were observed in AD patients suggesting a possible role of *Malassezia* yeasts in eliciting and perpetuating eczema in already sensitized AD individuals (Reitamo et al., 2008 & Darabi et al., 2009). *Malassezia* extracts are not yet part of the standardized APT panel provided by ETFAD. No consistent correlation has been shown between HNAD and positive APT. In many trials oral antifungal therapy has been shown to improve clinical manifestations of AD, particularly in the context of HNAD, exacerbations during adolescence and young childhood, severe AD recalcitrant to conventional therapy, and presence of other atopic diseases. It is not clear yet if this is due to the anti-inflammatory effects of antifungals or due to their antifungal

(Kedzierska et al., 2008).

• Efficacy of topical antiseptic treatment • Efficacy of topical antibiotic therapy • Efficacy of application of gammaglobulins • Efficacy of oral antibiotic and antifungal therapy

Table 10. Relevance of skin flora for AD

IgE autoreactivity has been implicated in the immune pathogenesis and in particular perpetuation of AD. Striking similarities between environmental allergens and human proteins have been identified on molecular analysis of allergens, and IgE-reactive autoantigens against human proteins have been cloned from human epithelial copy DNA expression libraries. Autoantigens have been detected in IgE-mediated immune complexes in serum of AD individuals and release of autoallergens following tissue (skin barrier) damage has been reported. More importantly reduced levels of IgE autoallergen levels have been noted following successful treatment of AD. It is possible that following initiation of the AD immune and inflammatory cascade in skin and peripheral blood by environmental allergens, these mechanisms are then partially perpetuated by autoallergens. More studies are required in the future to allow any sensible conclusion (Reitamo et al., 2008).

#### **2.5 Contact allergens**

It is clear that AD individuals are at greater risk in developing irritant contact dermatitis than non-atopic subjects, as contact allergens are likely to penetrate the defective skin barrier more easily. In this context hand eczema has been reported to occur in higher frequency in AD patients. AD individuals, who are particularly employed in occupations involving wetwork are prone to develop an intractable hand dermatitis in their occupational setting leading to considerable occupational disability. Urticaria is frequently encountered in AD individuals, and an allergic basis is found more often in atopic subjects than in the normal population. Contact urticaria of hands may lead to exacerbation of clinical disease in AD particularly in food handlers and slaughterhouse workers (food allergens) as well as health care workers (latex protein sensitivity) (Burns et al., 2004).

There has been dispute about whether atopic individuals are at greater risk to developing contact allergic reactions. CAD has a reported prevalence of as high as 28% in certain European countries, and similarity in clinical symptoms between AD and CAD makes correct diagnosis of CAD a challenge and can easily lead to misdiagnosis. A recent PT study found that a family history of AD (85%), female sex (74%), and age 11-16 (63%) were

Trigger Factors, Allergens and Allergy Testing in Atopic Dermatitis 227

Consideration of CAD is recommended in each case of recurrent and recalcitrant clinical disease, and PT should be considered and offered to AD patients in those circumstances. However the relevance between a positive PT reaction and clinical severity of AD remains

AD is a common chronic skin condition associated with high morbidity and major public health implications. As prevention of disease is not yet a real option, reducing morbidity is main aim of treatment. Identifying the underlying pathomechanism of the individual's AD is very crucial. High levels of specific IgE antibodies and or total IgE levels in serum are significantly associated with severity of dermatitis in individuals with the extrinsic type of AD. Raised specific IgE antibodies can be detected in the peripheral blood for most trigger factors and allergens. Food and aeroallergens, microbes including *S. aureus* and *Malassezia* yeasts, contact allergens and autoallergens have been identified to trigger AD and

To date no standard test is available to diagnose AD. Sensitization to various allergens is a major part of triggering and perpetuating the inflammatory skin response in AD. Various tests have been developed to investigate the underlying type(s) of hypersensitivity reaction involved in AD patients. None of the available tests so far have proven sensitive and specific enough to identify reliably relevance between clinical reaction and test result. Allergy tests commonly used in practice include measurement of total levels of IgE and allergen specific

Precise understanding of these tests including their limitations together with accurate correlation of patient history, symptoms and signs are required in order to differentiate between allergy, intolerances and hypersensitivities, and achieve an appropriate clinical

In a recent meta-analysis filaggrin gene defects have shown to increase the risk of developing allergic sensitization, AD, and allergic rhinitis. The presence of filaggrin gene mutations correlated strongly with disease severity and treatment failure, and also increased the risk of asthma in AD patients. Gene testing for filaggrin gene mutations might be an additional way to identify atopic individuals in future. Restoring skin barrier function in filaggrin deficient individuals early in life may help prevent the development of

Boussault P et al. (2007). *Oat sensitization in children with atopic dermatitis: prevalence risks and* 

Burns T, Brethnach S, Cox N, Griffiths C (2004). *Rook's Textbook of Dermatology, (*7th ed.

Czarnobilska Ket al (2010). *A half of school children with "ISAAC eczema" are ill with allergic* 

Darabi K et al. (2009). *The role of Malassezia in atopic dermatitis affecting the head and neck of* 

Fonacier LS, Aquino MR (2010). *The role of contact allergy in atopic dermatitis*. Immunol

diagnosis. Results must always be interpreted in the context of clinical history.

sensitization and halt the development and progression of allergic disease.

Chapter 18). Blackwell Publishing. ISBN 0-632-06429-3

*contact dermatitis*. J Eur Acad Dermatol Venereol; 4.

*associated factors* Allergy 2007: 62: 1251–1256

*adults*. J Am Acad Dermatol;60(1):125-36

Allergy Clin North Am;30(3):337-50

perpetuate so the underlying immune and inflammatory cascade of AD.

IgE levels in serum (RAST), SPT, APT, PT and DBPCFC.

to be answered.

**3. Conclusion** 

**4. References** 

predisposing risk factors to contact allergen sensitization. Another study evaluating contact sensitization in a series of atopic pediatric patients, that were patch tested, identified 43% positive reactions without commenting on clinical relevance of these reactions (Fonacier & Aquino, 2010 & Jacob S et al., 2008). AD individuals can develop sensitivity to a variety of contact allergens such as topical medicaments including emollients and corticosteroids as well as fragrances, particularly in the presence of recalcitrant periorbital dermatitis. A positive past medical history of AD (44% in patients with periorbital dermatitis) has been found to be a predisposing factor for periorbital dermatitis when compared with all patchtested individuals (29% with peri-orbital dermatitis). Statistically significantly more patients with AD were found in the group of patients with than without periorbital dermatoses. The periorbital region is a prime location for AD and in consequence a defective skin barrier alleviates sensitization to contact allergens as well as aeroallergens.

Hand eczema and compositae allergy may be more common in AD, whereas allergies to topical corticosteroids and antiseptic solutions are only positive in a small subset of AD patients (15%) (Fonacier & Aquino, 2010).

Oat sensitization and its clinical manifestations in the form of digestive, respiratory and cutaneous symptoms (including CAD) has been identified in 15-20% of AD children, compared to none in the normal population. It is likely to be due to repeated applications of oat proteins through topical emollients and hygiene products on a predisposed impaired epidermal skin barrier of AD individuals. Oat can also be added to the list of food products (e.g. peanut, ovalbumin, almond) responsible for FA triggered by a possible percutaneous sensitization. Avoiding application of topical containing oat protein products in AD infants is paramount in reducing sensitization to oat (Boussault P et al., 2007).


Table 11. Factors that make a diagnosis of CAD likely

A lower frequency of positive quinoline allergy has been documented in AD individuals, whereas contact allergy to neomycin among atopic subjects is usually found to be equivalent or slightly raised in comparison to non-AD individuals. AD subjects appear to have increased efficiency in orally tolerising haptens but are inefficient in orally tolerising proteins. The reduced contact allergy to quinoline in AD patients might be explained by a higher exposure of haptens in the gut and skin at a young age producing "hapten"-tolerance (McFadden & White, 2008).

History for CAD should always include the patient's personal hygiene environment, medical and medicament history as well as home and care giver environment. PT should be performed in all AD patients where CAD is considered and particularly in children with AD. However because of irritancy interpretation of PT may be difficult in AD individuals and the severity of AD might have an impact on the results obtained through PT. PT should always include the emollients used.

In summary more and more studies suggest, that CAD might occur as common in AD individuals and particularly in children with AD as in the general population. Consideration of CAD is recommended in each case of recurrent and recalcitrant clinical disease, and PT should be considered and offered to AD patients in those circumstances. However the relevance between a positive PT reaction and clinical severity of AD remains to be answered.
