Allergen Extract Analysis and Quality Control

Abstract

The increase in allergic diseases in Westernized Countries is an established phenomenon, which has been extensively documented by several large epidemiologic studies (Sicherer and Leung, 2010). Allergies affect nowadays a proportion of the general population as large as one out of five individuals. The most prevalent clinical expression of allergies include respiratory allergies, such as allergic rhinitis and asthma (Chu et al., 2010), skin allergies, such as atopic dermatitis (Spergel, 2010a), and food allergies (Chafen et al., 2010). The pathogenesis of allergic diseases, and the reasons for their increased incidence is partially known and include environmental and genetic factors (Kuriakose and Miller, 2010). In all cases, the hallmark of all these bone fide allergic diseases is the presence of specific antibodies of the immunoglobulin E (IgE) isotype against protein antigens, which are indicated as allergens on the basis of their capability to elicit allergic reactions. The presence in the biological fluid of IgE to a given allergen is indicated as “sensitization” to that allergen. In most cases, IgE are measured in serum, where they are more easily detected and also on the ground that allergy is a systemic condition, with clinically relevant expression in different individuals at different target organs (e.g., lower respiratory tract in the case of allergic asthma, nasal mucosa in the case of allergic rhinitis, etc.) (Pucci and Incorvaia, 2008) depending on organ-specific characteristics, which have been only partially identified. The correct identification of sensitizing allergens is required to put in action the most efficient strategies to counteract the clinically relevant effect of allergies as well as their remarkable effects on the quality of life (Cummings et al., 2010). Useful measures include allergen avoidance, when applicable, proper symptomatic therapy and, most importantly, allergen specific immunotherapy, which is the only intervention capable to actually modify the pathogenic mechanisms of allergic diseases and their natural history, known as the allergy march (Spergel 2010b). IgE can be measured in vivo with prick testing and in vitro with immunochemistry testing. Notably, as compared to immunochemistry testing of other immunoglobulin classes, specific enhanced procedures have to be used for allergen specific IgE determination, due their concentrations in biological fluids, which is in the range of ten to hundred thousand times lower as compared to the most represented immunoglobulins, e.g., those belonging to the IgG isotype. A major issue to be considered in allergen-specific IgE determination is the quality of the antigen to be used for testing. Indeed allergens, which are encountered by patients in natural context are complex mixtures of relatively heterogeneous proteins. This fact poses several problems to Manufacturers of allergen extracts, including the