Microbial metabolites Why doesn't the immune system destroy those who have settled inside us?
There are two kilograms of microbes in the intestines of an average person, and there are about as many bacterial cells in the body as there are their own. Microorganisms help us with digestion, fight infections and even, as studies show, affect our mood. But if they are not properly fed, allergies, obesity, depression, heart disease may appear, and this is only a small part of the possible consequences. Microbes can be dangerous — they cause diseases, because of them we can get poisoned. So why doesn't the immune system destroy those who have settled inside us?
In the case of gut microbes, they suppress immunity by triggering induced regulatory T cells (iTregs), a type of cell that controls the development of immune tolerance.
It is freely available information - about T cells. Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3221948/
Plus, as far as I know, they are conditionally pathogenic, for example, E. coli, if it enters the bloodstream, then it should normally be destroyed by the immune system
@morphism Do I understand correctly that iTregs is the cause of all bowel-related problems?
@ekaterina-gribacheva If the immune system does not find, for example, butyric acid - a metabolite of beneficial bacteria - it automatically turns on the inflammation mode. First of all, she is looking for a problem (which pathogen got into the environment), and then a solution (how to kill it). But if bacteria die due to a lack of dietary fiber, then there is no one to kill. And here a problem arises, since the immune system is sharpened for the destruction of foreign microorganisms, it cannot supply the microbiota with the necessary dietary fiber.
@ekaterina-gribacheva Tregs suppress activation, proliferation and cytokine production of CD4+ T cells and CD8+ T cells, and are thought to suppress B cells and dendritic cells.
why pathogenic bacteria do not induce the production iTregs?
@argentum Unfortunately, they do. Though Tregs protect the human host against excessive inflammation, they probably also increase the risk of pathogen persistence and chronic disease, and the possibility of disease reactivation later in life. Mycobacterium leprae and Mycobacterium tuberculosis, causing leprosy and tuberculosis, respectively, are among the most ancient microbes known to mankind, and are master manipulators of the immune system toward tolerance and pathogen persistence.