Allergenicity of food allergens and routes of sensitization to them
There are four routes of IgE-dependent sensitization to food allergens: (1) gastrointestinal; (2) respiratory; (3) transcutaneous [5; 6: 7], and (4) rare genitourinary [8]. Accordingly, clinical manifestations are localized in the same target organs, including cardiovascular and central nervous systems, if anaphylaxis occurs [3: 7; 9; 10]. Not all food proteins are allergens, therefore subject to allergenicity of food allergens is very important. Allergenicity is the allergen’s ability to induce a non-adequate adaptive immune response, characterized by the overactivation of the immune system, absence of protective effect, and development of allergic inflammation and possible own tissue damage instead. Allergenicity is evaluated by many methods such as bioinformatics analysis, serological assays, mass spectrometry, cell experiments, animal models, etc. [11; 12; 13]. There are some families and three classes of food allergens [14]. Class 1 food allergens (cow’s milk, peanut, hen’s egg, etc.) are oral allergens that cause sensitization via the gastrointestinal tract and display severe clinical symptoms. Class 2 food allergens (e.g., birch) are aeroallergens that evoke sensitization via the respiratory tract and exert not severe cross-reactions termed ”oral allergy syndrome,” or ”pollen food allergy syndrome” [15; 16]. Class 3 food allergens (e.g., small food proteins, additives, and contaminants) not having the capacity of cross-reactivity, which sensitize via the unified airway or skin and frequently cause occupational allergies [14].
Food protein allergenicity depends on many factors: antigenic structure (multiple epitopes capable of linear IgE binding), molecular weight lower than 70 kDa, stability, solubility in water, interaction with lipids, abundance in food, biochemical characteristics of proteins allowing to pass the extremes of food processing and proteolysis by digestive enzymes, combination with adjuvants in food, ability to promote the production of high levels of allergen-specific IgE and high-affinity allergen-specific IgE, pathologic imbalance in the target organ’s microbiota, damaged mucosal barriers, decreased enzyme secretion, deficiency in sIgA, atopic predisposition of a person, etc. [17; 18].
”The Big Eight” food allergens cause about 90% of all food-allergic reactions. They are cow’s milk, hen’s eggs, peanuts, tree nuts, wheat, fish, and crustacean shellfish. Food allergies to cow’s milk, egg, and wheat often are outgrown as grown-up children acquire allergen tolerance, whereas allergies to peanuts, tree nuts, fish, and shellfish commonly persists over a lifetime exhibiting the high association with anaphylaxis [1; 16; 19].