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Monday, October 15, 2007

Why Some Foods Are More Allergenic Than Others

An absolutely fascinating piece of research was just published in The Journal of Allergy and Clinical Immunology

(DOI: 10.1016/j.jaci.2007.08.019.) "Evolutionary distance from human homologues reflects allergenicity of animal food proteins," by John Jenkins, Heimo Breiteneder, and Clare Mills.

Articles explaining the research can be found in more - - or less - - straightforward English on those sites.

The investigating team compared several types of proteins across a wide variety of types of animals, from insects to mammals to humans. If the protein was at least 55% identical to the human protein, few if any allergic reactions were produced. But proteins less similar triggered the immune system of the human body in some people.

"This explains why people who are allergic to cow's milk can often tolerate mare's milk but not goat's milk", said Dr Clare Mills of the Institute of Food Research. "Proteins in horse milk are up to 66% identical to human milk proteins, while known allergens from cows and goats are all less than 53% identical to corresponding human proteins.

Overall, the researchers believe that the reason why just a few percent of humans have milk allergies is that the protein similarities are so close to the border of tolerance.
"Animal food proteins lie at the limits of the capability of the human immune system to discriminate between foreign and self proteins", said Mills.

The researchers looked at all the main types of proteins and made a major discovery.
For the first time the researchers found that the majority of animal food allergens could be classified into one of three protein families. Tropomyosins, proteins found in muscle tissue, are the most important family.

"Tropomyosins in mammals, fish and birds are at least 90% identical to at least one human tropomyosin and none have been reported to be allergenic. 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", said Dr Heimo Breiteneder of the Medical University of Vienna.

EF-hand proteins form the second largest animal food allergen family. Those in birds and mammals are not allergenic, while those in frogs and fish can cause allergy. The third animal food allergen family, caseins, are all mammalian proteins from milk. The researchers analysed milk from rabbits, rats and camels as well as sheep, goats, cows and horses.

In previous analyses of plant food allergens published in 2005, the scientists found that most belong to a highly restricted number of protein superfamilies. The research will make it easier to identify new allergens and help explain how they trigger an immune response.

I reported a year ago that work was underway to develop a vaccine for allergies, but that 7 to 10 years was likely to be needed. See Cure for Allergies? Don't Hold Your Breath. I'm not sure if this work makes that wait any shorter. However, it's extremely promising research and a critical needed step.

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