How Microbiota Communicates With Our Immune System

Did you know that one of the central roles of the gut microbiota is the regulation of the immune system? How does the immune system “sense” the gut bacteria? Even if this interplay occurs in the intestine, can it affect the entire immune response of the body? In this step you will discover the responses to these questions!

This communication starts at the very beginning of life when we acquired the first colonizers through the birth canal from the mothers. The acquisition of these bacteria and their cross-talk with our cells results essential for the proper development of the immune system in childhood. But it is also important in adulthood as the gut microbiota continues shaping the activity of the immune system throughout our whole life.

Considering the profound basis of this relationship, one can understand why changes in the gut microbiota composition have been linked to altered immune responses that are believed to participate in the onset of immune-based diseases. This implies the fact that the immune system can recognize changes that occur within the bacterial population. So, let’s start from the beginning: how does the immune system manage to recognize intestinal bacteria?

Pathways of Communication

The immune system to adequately protect the body, it first needs to recognize the intestinal bacteria. This recognition occurs through molecular structures present in bacteria and that scientists have named “microbiome-associated molecular patterns” (MAMPs). The best examples are the bacterial cell wall components, like lipopolysaccharides (LPSs). These structures are recognized via specific recognition receptors (PRRs) expressed on the surface of our cells.

Once recognized, the cells of the immune system will decide whether to trigger an inflammatory response counter towards the invaders or to favor the tolerance. This last occurs in the case of commensal bacteria. What the immune system does is block the inflammatory pathways to, this way, develop tolerance to their presence in the gut.

Bacterial Metabolites Modulating the Immune Response

The cells of our body are also trained to recognize additional molecules of bacterial origin, like microbial metabolites. As you have already learned, gut microbes can transform compounds from our diet and generate a bunch of different metabolites. Some of these metabolites, like the short-chain fatty acids (SCFAs), can activate different cellular signaling cascades that involve the immune response.

All in all, scientists so far suggest that the gut microbiota and its derived-metabolic activities can influence immune activation by using different pathways. Given the crucial role of the immune system in human health, the modulation of these different pathways by gut microbiota opens novel options to favors our health in the near future.

Gut Microbiota and Autoimmune Diseases

One of the functions of the immune system is to protect the body by responding to invading microorganisms, and accordingly, the immune response is directed towards an external factor. In some cases, however, immune cells make a mistake and attack our structures. This response characterizes a variety of autoimmune diseases (p.e., inflammatory bowel disease, rheumatoid arthritis, type 1 diabetes, or celiac disease).

Although the mechanisms behind the onset of autoimmune diseases remain unclear, the new hypotheses point to the conjunction of genetic and environmental factors. Specifically, more and more studies have found disturbances in the gut microbial ecosystem associated with these conditions. These observations led to hypothesize that changes in the gut microbiota may contribute to the disease pathogenesis (the development of the disease), but also that these changes in the microbiota might precede their onset. If you are interested in the relation of the gut microbiota with some of these autoimmune diseases, read the linked PDF.