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Irritable bowel syndrome (IBS) is a common condition that affects the digestive system. It causes symptoms like diarrhea, stomach cramps, constipation, and bloating, causing distress to the patients. Guy Boeckxstaens, a gastroenterologist at KU Leuven, and his colleagues have recently proposed that stomach pain is caused owing to a localized allergic reaction to food in the gut.
To test their hypothesis, Boeckxstaens and his team had infected one set of mice with harmful gut bacteria and fed them egg white protein (antigen). This group represents people with food allergies. The control set of mice were just infected with harmful gut bacteria. When the first batch of mice recovered from the gut infection, they were again fed with the same antigen. Scientists observed that this time the mice experienced abdominal pain, which was measured by studying the muscle contractions of their stomach. Such contraction was not present in the control group of mice.
On further investigation, researchers found that after the onset of gut infection, the egg white proteins trigger a chain of reactions similar to food allergies. After the second exposure to egg white antigen to the mice, the antigen attaches to the antibodies (IgE) bound to mast cells. The mast cells (immune cells) get activated and released histamine that stimulated the nearest gut neurons. As a result of which the gut got extremely hypersensitive, which the body experienced as stomach pain.
The study was extended to human beings, whereby, Boeckxstaens’s team injected common food antigens, i.e., soy, gluten, milk, and wheat, into the rectosigmoid mucosa of patients with IBS. Researchers found that food antigens induced mast cell activation and local edema. This research highlights a peripheral mechanism that underlies food-induced abdominal pain. It also paved the path for new treatment procedures for IBS and other related abdominal pain disorders.
A similar study was conducted by Bana Jabri, a pediatric gastroenterologist and mucosal immunologist at the University of Chicago, in 2019. Jabri and her team reported that ingestion of gluten caused a strong immune response among patients who were intolerant to gluten. This intolerance subsequently caused abdominal pain and nausea.
Giovanni Barbara, a gastroenterologist at the University of Bologna who was involved in the IBS study on humans explained that the intestinal tissue biopsies of the IBS patients showed activated mast cells. In normal conditions, mast cells are activated in response to a wound or pathogenic infection of the host and, thereby, release chemicals such as histamines to the targeted sites. Researchers found that mast cells were activated in IBS patients who did not have any active infections. These cells were also present in close proximity to nerve cells and caused them to fire excessively. Scientists found that the mucosal mediators increased the firing or hypersensitive reactions of the mesenteric sensory nerve and also initiated the Ca2+ mobilization in dorsal root ganglia in rats.