[Polymorphism in allergens].

Allergens are antigens that elicit an IgE-mediated immune response; they originate from diverse sources such as pollens, mites, molds, mammal exudates, insects and food. Allergenic molecules can contain several antigenic determinants, termed epitopes. Allergenic proteins have been discovered with polymorphisms, i.e., a mixture of similar molecules with minor variations in their amino acid sequences. These are called isoallergens or allergenic variants depending on the degree of similarity. Polymorphism may be defined by the presence of several alleles of the same gene or as families of related genes. Polymorphisms can have an important effect on the epitopes recognized by T lymphocytes, monoclonal antibodies and IgE of allergic patients. Individual polymorphisms can affect the basal level of allergenicity as well as the cross-reactivity with other allergens. The use of isoforms with low or total absence of IgE binding capacity but with high capacity to stimulate T cell response has been suggested as an alternative to the conventional immunotherapy for allergic diseases. Standardization of allergenic compounds can be affected by the differing proportions of isoforms in allergenic sources from different regions.