Why intestinal immunity begins to fight with regular food

The stomach can hurt because we ate something wrong, for example, something poisonous. Another reason is immune inflammation in response to infection: a pathogenic bacterium has entered the intestines, and now the immune system is trying to expel it. But it so happens that the stomach begins to ache in response to a completely ordinary meal, without toxins and without pathogenic bacteria. This is called irritable bowel syndrome. It may be limited only by pain, but other symptoms such as diarrhea, etc., may also occur.

It is believed that the cause of irritable bowel syndrome is a malfunctioning immune system, which begins to react to ordinary food. But why does he start to react this way? Researchers from the Catholic University of Leuven and other European research centers write to Naturethat the cause may be a past bacterial infection.

In experiments, mice were infected with a pathogenic bacterium Citrobacter rodentium, after which the mice began to suffer from intestinal upset in response to the usual egg white. It turned out that after infection, the mouse intestine began to pass substances that it should not pass: food molecules (the same egg white) penetrated under the intestinal epithelium, where they were met by immune cells. They reacted to this as a threat: antibodies to egg white appeared in the blood, and nerve endings in the intestinal wall generated pain signals.

The antibodies against egg white were immunoglobulins E (IgE), often referred to as allergic antibodies. If they were disposed of in one way or another, the intestines and its immune system did not suffer from food. On the contrary, if the IgE level was artificially raised, then the mice developed irritable bowel syndrome even without prior infection.

Further experiments showed that infection and egg white caused the mast cells of the intestinal wall to expel many different molecules, including histamine. Mast cells are a class of immune cells that sit next to blood vessels and nerves, participating in allergic inflammation. Histamine and other signaling substances they release cause swelling and sensitization of painful neurons.

Another series of experiments involved volunteers: eight healthy people and twelve people with irritable bowel syndrome. They were injected directly into the intestines with suspensions of gluten, soy, wheat, milk. Those who suffered from irritable bowel syndrome developed cramps and bloating, and they all showed signs of an immune response to at least one food. (Among healthy people, only two people had such a reaction.)

In patients with the syndrome, the bacterium Staphylococcus aureus, which is known to stimulate a nonspecific response in T cells, was found twice as often as in healthy people. That is, because of staphylococcus, the immune system begins to work actively, but not against a specific bacterium, but, so to speak, in general. The nonspecific aggressiveness of the immune system, obviously, was the reason that in response to ordinary food the intestines began to suffer.

The new data does not explain some of the characteristics of irritable bowel syndrome, such as why it occurs more frequently in women than in men. On the other hand, the syndrome itself manifests itself in different ways, someone with constipation, someone with diarrhea, etc. Finally, there are many infectious intestinal bacteria, and it would be interesting to know which ones are more conducive to irritable intestines, and which less. But in any case, already now you can think about how to calm down the confused immunity and what is better to act on: IgE antibodies, mast cells or histamine receptors.

Based on materials Nature.

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