How peanuts cause allergy

Research by a scientist in the UK helps understand a hitherto unexplained mystery of food allergy. He has discovered the route and type of transport taken by peanut proteins through the gut to the immune system. This route favours an immune response and helps explain why peanuts are one of the most allergenic foods.

Dr Claudio Nicoletti from the Institute of Food Research (IFA) said: "Food allergy is an immune system over-reaction to a food protein. The cause of this over-reaction has remained a mystery. Our aim was to identify the route that proteins from digested peanuts take to the lymphoid tissue of the gut where immune responses start."

First, using a digestion model, the research team found that digestion through the stomach and small intestine produces large amounts of soluble protein and intact protein bodies - large particle-like structures. Second, by labelling them with gold, Dr Nicoletti found that peanut proteins are delivered at high speed through the gut via M-cells.

M-cells are effective at rapidly delivering foreign bodies, including proteins, to defence cells. Protein bodies 'hitching a ride' with M-cells are therefore likely to trigger defence cells into action. "Peanut proteins are delivered quickly, in large amounts and in highly immunogenic form to immune cells," said Dr Nicoletti. "This may be important in explaining strong allergic reactions to peanuts."

Peanuts frequently cause severe reactions, including potentially lethal anaphylaxis. The allergy can be so severe that very tiny amounts can be enough to trigger a response.

The neighbouring cells to M-cells are enterocytes. Proteins delivered via these cells are processed to form peptides and when presented to the immune system are likely to induce tolerance. "This research shows that antigens have the ability to dictate the route of transport, and in doing so the type of immune response that follows," said Dr Nicoletti.

The work was supported by a strategic grant from the Biotechnology & Biological Sciences Research Council, UK, and intramural funds of the University of Siena, Italy. The results were published in Biochemical & Biophysical Research Communications.