The immune system and microbiota

The intestinal flora or ‘microbiota’ consists of billions of microorganisms forming an actual organ. Most of these are found in the intestine where they complete the digestion of food, regulate the intestinal function, produce vitamins, eliminate waste and harmful substances, protect against pathogenic germs, keep our immune system functioning, and influence our brain and emotional state.

Laboratory animals bred in completely sterile environments die shortly after being inserted in a normal environment, due to trivial infections, because their immune system is not activated and hasn’t yet learnt to defend the body. Humans too would be particularly susceptible to attacks by pathogenic germs in the absence of a suitable defence, ensured by the stimulus provided to the immune system by the microbiota. The intestine therefore not only absorbs food, but also constitutes the main organ of the immune system insofar as it hosts more than 70% of the immunocompetent cells. This concentration is the consequence of the need to protect the large intestinal surface, a potential entryway for harmful substances from the outside world.

The gut microbiota contributes to many complex processes considered vital for the body: it hinders the development and spread of numerous harmful microorganisms, preventing intestinal and general infections; it inactivates potentially carcinogenic compounds; it produces a growth factor that promotes child development; it protects against pathogenic agents; it strengthens the immune system; it completes the food disintegration and digestion process, contributing to the breakdown of proteins, sugars and fats; it produces key molecules essential for our health, and in particular B-group vitamins.

 

The main defence mechanisms activated by probiotic bacteria against pathogenic bacteria include the enhancement of the barrier effect, of the intestinal mucosa, competitive exclusion and resistance to colonisation by potentially harmful germs. The microorganisms of the intestinal flora, and in particular lattobacilli, produce lactic acid from the carbohydrates in foods, and bacteriocins (substances with an antibacterial and antifungal action that counteract the proliferation of other microorganisms). In addition, probiotics bind to the intestinal mucosa, completely covering it and anchoring themselves to the receptors of the mucosa by means of adhesins. As such, the numerous and sometimes pathogenic bacterial strains that continually reach the intestine with food, find the receptors already occupied, fail to settle and are therefore eliminated from the intestinal flow with stools.

Any alteration of a healthy microbiota due to the prevalence of certain bacteria over others, known as gut ‘dysbiosis’, plays a role so crucial as to be considered the ‘mother of all diseases’.

To help restore the balanced condition of the gut ecosystem, and in particular of the microbiota, it is important to adopt a rebalancing program that consists in following a proper diet, which also involves the use of probiotics, nutritional supplements and prebiotics. The latter contribute to the establishment, development and activity of a healthy microbiota. These include mainly soluble dietary fibres.