It's no coincidence that peanut is one of the most common allergens, not tolerated by 1% of the world's population. Humans, even those without allergies, appear to have a genetic predisposition to produce antibodies to ARA h2, the peanut protein creating the strongest reactivity, according to new work published in the journal Science Translational Medicine.
“Public antibodies,” whose structure is conserved from one individual to another
“ We were completely surprised by how the story unfolded", says Sarita Patil, an allergist who led this new work. The story of this research goes back a decade, when the team was looking for protective antibodies capable of inducing long-term peanut tolerance. Instead, they accidentally discovered antibodies that specifically target the Ara h2 protein and that share much of their structure from one person to another, despite genetic variations.
These so-called "public" antibodies, because they are widely shared within the population, are just beginning to be described in other diseases. The idea eventually emerged after several years of work that public antibodies could show us how multiple pathways can be genetically preprogrammed to result in nearly identical antibodies.", continues Sarita Patil.
Peanut antibodies found in non-allergic babies
When we eat, healthy humans produce antibodies that specifically target the food we eat, according to numerous scientific publications. These are called IgG (immunoglobulins, the scientific name for type G antibodies), meaning they do not cause an allergic reaction, unlike their counterparts, IgE. The purpose of normal IgG production against food antigens is not fully understood., admits Sarita Patil.
The process by which IgG can transform into IgE is called sequential switching, and while it is not entirely understood, it allows these antibodies to better retain memory of the response. The researchers thus found both anti-Ara h2 IgG and IgE in the blood serum of 22 children and adults with peanut allergies. Logical up to that point. But, surprisingly, similar IgGs were also present in the serum of half of the 45 healthy babies examined, who were introduced to peanuts in the first year of life.
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Mysterious evolutionary origins
“ We believe these results indicate that we are genetically preprogrammed through our antibody genes.", interprets Sarita Patil. It remains to be seen when this phenomenon developed during evolution, whether it is present in other mammals or if it is specific to humans. The question of the cause remains open for now.
“ Although we found this particular epitope on peanuts, it is possible that it was present in other foods even before the modern peanut plant was found 2,000 years ago in South America." suggests Sarita Patil. " It is also possible that there is another peanut-like epitope in a completely different organism, such as a bacterium, that we have learned to recognize during evolution.. » Our sensitivity to peanuts would in this case be a bias resulting from a defense genetically inscribed in the human species against a pathogen.
“ For us, this work was like a mystery box in which we kept finding new treasures at every level, which challenged our preconceived ideas about how antibodies against food develop.", summarizes the allergist.
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