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].