Thursday 2 August 2018

Microbiome regulates the immune system

A new study has been published in the journal Immunity which shows that the microbiome helps to adjust our inflammatory response. It balances the immune response and protects the gut from inflammation. 

Pathological micro-organisms, such as Salmonella, evoke an inflammatory immune response that is directed at eliminating the relevant micro-organism. But an inflammation resulting from an immune response, especially in the intestine, can damage the healthy tissue. It makes the gut barrier vulnerable. This can also lead to auto-immune and inflammatory diseases, including inflammatory intestinal disorders. This occurs through interactions between certain bacteria of the microbiome, the epithelial cells on the inside of the intestine and the cells of the immune system.


Antigen-presenting cells 

Antigen-presenting cells are immune cells that direct other immune cells, called T cells, to mount an effective immune response. This triggers an appropriate inflammatory response to fight pathogens. They also direct anti-inflammatory T cells, also known as regulatory T cells, to limit certain inflammatory immune responses, such as those against the food we eat. They are also able to turn off unwanted inflammatory immune responses. 


What does the microbiome do?

The microbiome helps to adjust the inflammatory response by instructing the antigen-presenting cells to secrete the cytokine IL-10, an important anti-inflammatory molecule. IL-10 helps to maintain the balance of the various T cell responses. The result is a balanced response that can fight off an infection like Salmonella, but that is regulated to prevent damage to the healthy intestinal tissue.


The study 

The researchers found that the antigen-presenting cells of laboratory animals did not produce IL-10 when antibiotics were administered to them. A disruption of the microbiome was found to result in CX3CR1 and APC-dependent inflammatory Th1 cell responses, which resulted in worsening of a pathogenic infection.

Bacteria were then returned to the animals’ guts. Only colonisation with microbes that were able to attach to the epithelium was found to compensate for the disruption of the microbiome. They were cable of increasing the IL-10 production and therefore reducing the inflammatory response. Although microbes that are able to attach to the intestinal epithelium are thought of as possible pathogens, in this case it was found that the attachment of bacteria to the epithelium was not causing disease, on the contrary it was regulating the immune system.



It seems plausible that the microbiome has to be healthy for a balanced immune response. To protect us against infection, but also to limit potential tissue damage when the immune system tries to eliminate pathogens. The researchers are now actively looking for other mechanisms through which microbes can stimulate a well-balanced intestinal environment.