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As a legume, the peanut belongs to the botanical family Fabaceae; this is also known as Leguminosae, and commonly known as the bean, or pea, family. World annual production of shelled peanuts was 44 million tonnes in 2016, led by China with 38% of the world total. Atypically among legume crop plants, peanut pods develop underground (geocarpy) rather than above ground. With this characteristic in mind, the botanist Carl Linnaeus named the species hypogaea, which means “under the earth”.

For many of us, the peanut is a harmless legume to eat without complications. But for others, it can lead to life-threatening allergic reactions. But much is unknown about the nature of these reactions and a lingering question is where in the body the antibodies are produced that result in an allergic reaction?

Now American researchers have been trying to answer this very question. The research team used an endoscope to take tissue samples from the esophagus, stomach and small intestine of 19 peanut-allergic people taking part in an oral immunotherapy trial. Then they closely examined those cells and compared them with ones found in the blood.

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They found an extra-large accumulation of a special protein, an antibody called Immunoglobulin E (IgE), in the gastrointestinal tract. And it is an antibody that is linked to allergic reactions.

Using genetic analysis, the researchers were also able to confirm that the cells were being made in the stomach and the duodenum of the small intestine. This showed they were not being generated elsewhere in the body, and then traveling to the gut.

According to the researchers, much indicates that immunoglobulin E, in these individuals, is formed by the fact that some cells in the stomach shift from producing harmless antibodies to IgE antibodies instead.

Previous studies on mice hinted that certain immune molecules are made in the gut, but there has been scant evidence of that in people.

“This is the first time that we actually see what is happening in the gut” in people with peanut allergies.

– Cecilia Berin, an immunologist who studies food allergies at the Icahn School of Medicine at Mount Sinai in New York City

Reference:

Hoh et al. “Origins and clonal convergence of gastrointestinal IgE+ B cells in human peanut allergy”. Science Immunology, 2020. Doi: Immunology.sciencemag.org/lookup/doi/10.1126/sciimmunol.aay4209