Why is there a greater incidence of allergy to the tropomyosin of certain animals than to that of others?

Tropomyosin is a major allergen in various foods, implicated in a spectrum of mild to life threatening systemic reactions. The incidence of allergy to tropomyosin varies greatly by species, with sensitivity to crab, shrimp, cockroach, and dust mite tropomyosins, among others, being the highest, while tropomyosins in vertebrate species are considered non-allergenic. We have analyzed the possible fragments which may result from Pepsin A digestion of tropomyosins from various species and find that larger fragments of the tropomyosins from crab, shrimp, cockroach, and especially, dust mites will probably survive gastric digestion, compared to those from, for example, chicken, cattle, rabbit, or fish. These larger peptide fragments may enter the bloodstream and assume a three-dimensional structure whose stability approaches that of the intact molecule. Antibodies, including IgE, would be expected to be produced specifically against stable regions of the tertiary structure. We propose that this is a plausible explanation for the greater ability of the larger molecules derived from invertebrate tropomyosins to trigger an immediate hypersensitivity response.