Factors Influencing the Allergenicity and Adjuvanticity of Allergens

Stephan Deifl; Barbara Bohle

Disclosures

Immunotherapy. 2011;3(7):881-893. 

In This Article

Allergenicity

In this article, we define allergenicity as the property of being able to induce a Th2 response and subsequent production of allergen-specific IgE antibodies. Usually, the presence of allergen-specific IgE in serum is paralleled by the property of an allergen to induce clinical reactions. However, there are circumstances where this is not the case. If IgE antibodies only react with a single epitope; no cross-linking of IgE bound to the surface of effector cells can occur. Furthermore, IgE antibodies specific for carbohydrates on glycosylated allergens exist and cause problems in in vitro test systems for allergy diagnosis due to broad cross-reactivity.[33] On the other hand, in many cases, IgE antibodies specific for carbohydrate determinants of allergens do not induce mediator release.[34,35]

Complex allergen sources contain only a limited number of allergens that induce IgE antibodies in more than 50% of the allergic individuals, so-called 'major' allergens. 'Minor' allergens are less frequently recognized. However, the definition of major and minor allergens may differ between diverse populations of patients and should always be studied in a sufficiently high number of individuals. In view of the limited number of major allergens, one is tempted to assume that they share common characteristics that provide them with allergenic potential. Intense efforts have been made to identify common features and physicochemical parameters, such as the isoelectric point (pI value), hydrophobicity, protein stability, structural elements, molecular surface motifs, glycosylation, dimerization/oligomerization and enzymatic activity have been suggested. In addition, allergenicity may also depend on the capacity of allergens to bind lipids or to activate the innate immune system through signaling pathways of PRR, such as Toll-like receptors (TLRs) or C-type lectin receptors. Another interesting concept suggested that a lack of homology to bacterial proteins could be a common denominator for allergenicity.[36] The sequence comparison of allergens and bacterial proteins revealed that, in contrast to randomly selected control protein sequences, allergens have no or very few bacterial homologs. Consequently, allergens might be recognized by the human immune system differently from proteins with related bacterial homologs. Some examples of features suggested to underlie the phenomenon of allergenicity will be illustrated in more detail below.

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