The Evolution of Food Allergy

Why are some foods more allergenic than others?  Some propose that in sufficient amounts, any protein may stimulate an allergic response.  Others postulate that the structural properties of the protein are the main determinant.  One fascinating study looked at the differences in allergens in species with varying evolutionary distance from humans.  Muscle proteins called parvalbumins are either alpha (mostly fish, amphibians) or beta (mostly birds and mammals).  The difference between these parvalbumins makes it more likely that the alpha parvalbumins will be recognized by the immune system as non-self.  Likewise the tropomyosins of invertebrates (cockroach, dust mite and crustaceans) bear little similarity to vertebrate tropomyosin which also appears to account for the allergenic potential of these proteins.  Evolutionary distance is related to molecular differences which in turn forms the basis for the stimulation of the immune response.