07 October 2008

The DNA of the intestinal microflora stimulates the immune response

The number of bacteria inhabiting the body of a healthy adult – intestinal microflora, as well as biofilms covering the skin and mucous membranes – many times exceeds the number of cells of the body itself. At the same time, the intestines are normally inhabited by 300 to 500 species of "beneficial" bacteria that are not attacked by the immune system, necessary to ensure normal digestion, and commensal bacteria that do not benefit, at least explicitly, but are also completely harmless to the "host".

The body needs symbiont bacteria, but it needs to get rid of pathogenic microbes, so the immune system must somehow distinguish "good" microorganisms from pathogenic ones.

One of the functions of symbiotic bacteria is to protect the body from pathogenic microorganisms penetrating from the outside. One of the mechanisms of such protection is carried out through the interaction between commensal bacteria and certain immune cells. This interaction is mediated by the binding of bacteria considered useless tenants with T-lymphocyte surface receptors, known as Toll-like receptors (TLR).

In healthy people, a certain type of T-cells localized in the intestine (regulatory T-lymphocytes, T-reg) recognizes symbiotic microorganisms and keeps the immune system from attacking them. When an infection enters the body, T-lymphocytes switch to the destruction of foreign bacteria. The factors regulating the switching of the mechanisms of action of these cells have not been clear until now.

Scientists at the National Institute of Allergy and Infectious Diseases of the USA, working under the guidance of Dr. Yasmine Belkaid, have deciphered the mechanism that switches intestinal T-lymphocytes to fight pathogens. They found that during the development of the infectious process, the DNA of normal microflora bacteria binds to one of the types of Toll-like receptors on the surface of intestinal immune cells – TLR9. Such binding in the presence of a pathogen prevents the formation of T-reg cells and stimulates the production of protective T-lymphocytes that cleanse the body of pathogenic microorganisms.

Thus, the DNA of symbiont bacteria acts as a natural adjuvant, stimulating the activity of T-lymphocytes and directing it to the destruction of pathogens.

While in order to maintain the health of the body, the immune system must respond to the penetration of pathogens into the body, immune reactions directed against symbiont bacteria can cause serious problems. For example, it is believed that one of the reasons for the development of a number of inflammatory bowel diseases, such as Crohn's disease, are immune reactions to symbionts.

Understanding the mechanisms of interaction between the intestinal microflora and the immune system opens up new possibilities for using beneficial bacteria as therapeutic targets for the development of oral methods for the treatment of infectious and autoimmune diseases.

The article by JA Hall et al. "Mandatory DNA limits regulatory T cell conversion and is a natural adjuvant of intestinal immune responses" is published in the journal Immunity.

Portal "Eternal youth" http://vechnayamolodost.ru / based on ScienceDaily – DNA Of Good Bacteria Drives Intestinal Response To Infection


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