In a path-breaking finding that could help develop foods free from allergies as well as allergy therapies, scientists have found that the evolutionary distance of animal proteins to human proteins determines how likely they are to set off a food allergy.

While the most common food allergens in infants are cow’s milk and hen’s eggs, in adults, they are fish and seafood.

Researchers led by Dr Clare Mills, of the Institute of Food Research in Norwich, the United Kingdom, used sequence-based homology methods to
classify food allergens into families. They then conducted in-silico analyses to identify supposed relationships in protein sequence, structure and allergenic properties.

They found that, overall, only an animal food protein that is less than 54% identical to a human equivalent could become allergenic.

In simpler and practical terms, this explains why people who are allergic to cow’s milk can often tolerate mare’s milk, but not goat’s milk. Proteins in horse milk can be as much as 66% identical to human milk proteins, while known allergens from cows and goats are all less than 53% identical to their corresponding human proteins.

Dr Clare Mills and her co-researchers also found that most of the major animal-derived food allergens could be classified into one of three protein families – tropomyosins, EF-hand proteins, and caseins.

Among the tropomyosins – which are proteins found in muscle tissue and deemed the most important family – the team found a link between allergenicity and class of the animal from which it originates.

Tropomyosins in mammals, fish, and birds were found to be at least 90% identical to at least one human tropomyosin, and none has been reported to be allergenic, according to co-researcher Dr Heimo Breiteneder, of the Medical University of Vienna. In contrast, the allergenic tropomyosins are all from invertebrates such as insects, crustaceans, and nematodes and at most are only 55% identical to the closest human homologue.

Regarding the EF-hand proteins, the researchers found that those in birds and mammals are not allergenic to humans, while those in frogs and fish could be.

Caseins, the third family of animal food allergen, are all proteins from the milk of mammals. The researchers looked at milk from rabbits, rats, and camels as well as sheep, goats, cows, and horses.

The team concluded that “animal food proteins lie at the limits of the capability of the human immune system to discriminate between foreign and self proteins.”

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