Today we know that the intestine represents one of the most important immune bulwarks of the organism. Suffice it to say that with its surface of about three hundred square meters, this organ hosts something like one hundred thousand billion microorganisms and produces roughly 60-70% of the body's immune cells.
At the intestinal level, in fact, there are innate (or non-specific) and adaptive (or specific) immune systems which guarantee a correct response of the intestinal mucosa following the entry of all that is recognized as foreign and dangerous. course of the article, the intestinal immune system is made up of more or less specific cells and systems whose objective is one: to protect the organism from the attack of external aggressors (for example, bacteria, viruses, etc.).
- represents one of the important "dividing lines" between the external and internal world of our organism. In order to protect it from external attacks, an efficient and organized defense system is essential., are aggregated and organized to ensure the activation of an immune response when necessary.
GALT includes mesenteric lymph nodes, intraepithelial lymphocytes, lymphoid cells of the intestinal submucosa and especially Peyer's plaques, which constitute the operational center of the intestinal immune response.
Peyer's patches are distributed in the submucosa from the pylorus to the ileocecal valve, gradually increasing in concentration as one approaches the end of the small intestine.
B lymphocytes and other APC cells (antigen-presenting cells, such as macrophages and dendritic cells) abound within Peyer's plaques; these cells have the task of recognizing foreign molecules and processing them in order to activate the T lymphocytes, which are particularly able to "eliminate the threat and" activate the production of antibodies which are also present at the level of Peyer's plaques.
Interposed between the epithelial cells of the intestinal mucosa, covering the Peyer cells, are the so-called M cells, without the brush border and responsible for recognizing antigens, discriminating what is safe from what represents a potential threat.
Everything that is unsafe is present in the intestinal lumen must therefore be brought into contact with the immune cells present in the mucosa and submucosa. For this purpose, the M cells internalize the antigens present in the intestinal lumen, which are phagocytosed by the macrophages and by the B lymphocytes present in the Peyer's plaques, which in turn will present the antigen to the T lymphocytes. of cytokines that will stimulate the B lymphocytes to produce IgA.
Please note
If the immune system's ability to distinguish harmful antigens from those that are not is lost, the immune response could turn to harmless food components or to "friendly" bacteria, triggering allergic phenomena or even chronic diseases.
Another particularly important aspect is that the T and B lymphocytes present in the Peyer's plaques, once activated by the antigen, are able to migrate into the mesenteric lymph nodes and from there pass into the systemic circulation (first lymphatic and then blood), thus distributing This is a very important aspect, since in this way any adverse reactions to food substances can also have repercussions on organs not directly connected to the intestine.
Intestinal mucus
The GALT is not the only defense system present at the enteric level. The intestinal secretion of mucus, in fact, represents another decidedly important factor in what is the defensive mechanism located in this organ.
Mucus is a thick and viscous substance whose task is to lubricate and protect the intestinal mucosa especially from the insults of acids and digestive products, but it is also capable of trapping and expelling from the intestine - thanks to the peristaltic movements - potentially microorganisms dangerous.
Paneth cells
Paneth cells are specialized epithelial cells present in the intestine. They are known to produce effectors of innate immunity, among which we find peptides with antimicrobial action (for example, α-defensins) which are active against both Gram positive and Gram negative bacteria .
Enzymes
In addition to what has been said so far, there is also the proteolytic action of enzymes of intestinal or hepatic derivation (poured into the small intestine through the bile), very important for "demolishing" peptide antigens, thus decreasing their immunogenicity.
Intestinal Bacterial Flora
Last, but certainly not least, we remember the intestinal bacterial flora, another of the fundamental elements of the intestinal immune system. These are the so-called "good bacteria" that colonize our enteric tract, constituting its flora. bacterial. These "friendly" microorganisms compete with the "bad" ones for nourishment and the sites of adhesion to the intestinal mucosa. In this regard, it is important that the intestinal immune system is able to "understand" which bacterial species to fight and which to tolerate within certain limits The role of the intestinal immune system, therefore, is also that of sampling, processing and presenting antigens in such a way as to allow the destruction of pathogens and, at the same time, to allow tolerance of non-pathogens.
Remember, however, that since the diet is able to deeply influence the composition of the enteric flora and the health of the intestinal mucosa, what we eat has important effects on the intestinal immune system, with repercussions that, as we have seen, can also be systemic.
