Acute (IgE-mediated) reactions to milk are due to various milk allergens. Caseins and whey proteins account for approximately 80% and 20% of total milk protein, respectively.[
60] The caseins include α
s1-, α
s2-, β- and κ-caseins (Bos d 8) and comprise 32%, 10%, 28% and 10% of the total protein, respectively. The most important whey allergens are α-lactalbumin (ALA, Bos d 4) and β-lactoglobulin (BLG, Bos d 5), comprising 5% and 10% of total milk protein.[
60–
62] Other minor milk allergens include bovine serum albumin (BSA, Bos d 6), lactoferrin and immunoglobulins (Bos d 7).[
17,
62] Sequential IgE-binding epitopes of the major milk allergens have been identified [
63–
67] and several have been investigated for mutational analysis.[
68–
70] The pathogenesis and causative allergens in non-IgE-mediated CMA, and milk allergy due to mixed IgE- and non-IgE mediated processes, are less well-understood.
Cooking diminishes the allergenicity of whey proteins, particularly that of BLG, presumably by denaturation of heat-labile proteins resulting in loss of conformational epitopes.[
71,
72] This may explain why many CM allergic patients tolerate extensively heated milk.[
73] Similarly, yogurt cultures, which ferment and acidify milk, contain less intact whey protein[
72], and therefore individuals with CMA exclusively sensitized to whey proteins may tolerate yogurt-based dairy products.
The specificity of soy allergens is variable and complex. As many as 28 different soy proteins were recognized as able to bind IgE in soy-allergic patients.[
74,
75] However, only a few of these proteins are considered “major” allergens, defined as those to which more than 50% of tested population reacted.[
76] In this context, only the birch-pollen-related allergens, Gly m 3, a profilin, and Gly m 4, a PR-10 protein, in addition to soybean hull proteins Gly m 1 and Gly m 2 (see below) have been officially accepted as soybean allergens by the International Union of Immunological Societies Allergen Sub-Committee (
http://www.allergen.org?Allergen.aspx). Several other soy proteins have been characterized, including storage proteins (β-conglycinin and glycinin, named Gly m 5 and Gly m 6, respectively),[
77–
79] the thiol-protease Gly m Bd 30k (possibly a major soybean allergen),[
80–
82] the soybean Kunitz trypsin inhibitor,[
83–
85] and 2S albumin soy protein.[
85] The two soybean major storage proteins, β-conglycinin and glycinin, are 7S and 11S globulins and account for about 30% and 40% of the total seed proteins, respectively. Sensitization to both of those allergens has been shown to be a potential indicator for severe allergic reactions to soy.[
86] Specific linear IgE-binding epitopes on some soy allergens have been identified,[
78,
81] and mutational analysis is underway.[
82]
Soybeans are also aeroallergens, although the pathology and allergen reactivity profiles are different for ingestion versus inhalation, where soy hull antigens (Gly m 1 and Gly m 2), not present in soy protein isolates, seem to dominate.[
87] The hydrophobic soybean hull proteins Gly m 1 and Gly m 2 have been described to be relevant in respiratory soy allergy, acquired through inhalation of soy proteins.[
88]
Soy allergy may also develop secondary to initial sensitization to birch pollen and resulting cross-reactivity (see below). A retrospective analysis of specific IgE to foods and inhalants from 273 children by The German Multi-Centre Allergy Study revealed that IgE sensitization to soy in infancy is relatively uncommon and mostly primary (generated by food ingestion). On the other hand, it is more frequent at school age due to cross-reacting pollen antigens via inhalation.[
89]