Adults of S. mansoni. The thin female resides in the gynecophoral canal of the thicker male. CDC.
Janet Fang 02 Nov 2015, 17:38

Some of the things that we’re allergic to – such as peanuts and pollen, for example – carry compounds that resemble proteins found in parasites. Turns out, our allergic reactions are actually maladaptive immune responses: To protect us, our bodies are attacking similar but harmless compounds. The findings were published in PLOS Computational Biology last week.

Various environmental and food proteins called allergens are recognized by an immune system antibody called immunoglobulin E (IgE). This part of the mammalian immune system is thought to have evolved as an additional rapid response mechanism to combat parasitic arthropods and worms called helminths. If IgE-mediated immune responses evolved to provide extra protection – and not to cause allergic reactions – then environmental allergens such as pollen should share key molecular properties with the parasite antigens that are specifically targeted by IgE in infected humans.

To test this, a team led by Nidhi Tyagi from the EMBL-European Bioinformatics Institute searched 2,712 known IgE antigens against a dataset of proteins from dozens of species of helminths and parasitic arthropods. This resulted in a list of 2,445 parasite proteins that show significant similarity in both sequence and structure with allergenic proteins. Then, the team measured antibody responses in blood collected from 222 people living in the fishing village of Namoni on the shores of Lake Victoria in Uganda. These community members were suffering from schistosomiasis, which is caused by the worm Schistosoma mansoni (pictured above). The blood was collected immediately before anti-schistosomiasis treatment and five weeks afterwards.

Turns out, a plant protein called BetV1 – the commonest allergen in pollen – is a target of IgE in humans infected with schistosomiasis. 

Allergens have been defined in the literature on many criteria, Tyagi explained to IFLScience, and this new paper adds to one of those definitions: environmental and food proteins that are similar to those parasite proteins against which IgE is an observed marker of protective immunity. Defining allergen-like molecules in parasites and understanding their link to the unregulated IgE response, the authors write, will help with the discovery and design of molecules for future immunotherapy in allergic conditions. 

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