Building a strong immune system involves many key components, including a well-balanced gut microbiome. The commensal bacteria and other microbes do more than simply shield and crowd out potentially harmful microbes; they play an active role in the development and maintenance of the immune system in the gut and beyond.

One important method for supporting the immune system comes from the gut microbiome’s metabolites and by-products that play many roles, including acting as signaling molecules for immune function. For example, short-chain fatty acids (SCFA) are produced from the metabolism of fiber and other food sources by many commensal species of bacteria. The SCFAs have anti-inflammatory properties and help maintain the integrity and function of the epithelium, inhibit the production of inflammatory cytokines, aid in the function of the microglia, inhibit the maturation of dendric cells, and promote normal antibody production.

The gut microbiota also aids in the development of the immune system and the maturation of immune cells. Commensal bacteria metabolites signal the development of granulocytes and monocytes in the bone marrow to prepare for the innate immune response. Animal studies using germ-free animals have found that when there is no microbiome, the immune system, especially in the gut, is underdeveloped, and there are fewer immune cells, which leads to the reduced ability to fight pathogens. In addition, when dysbiosis occurs, it can negatively impact the immune system and increase the risk of infection and disease.

A recent study looked at the relationship between the gut microbiome and immune health in patients with cancer. The participants were undergoing hematopoietic cell transplantation as part of their recovery from chemotherapy treatment, which leads to reductions in white blood cell counts and other immune changes, as well as harmful changes to the gut microbiome. Improving the state of the gut microbiome may improve the immune system, including those in whom the immune system has been compromised.

Autologous fecal microbial transplantation is the reinoculation of the gut microbiome from one’s own specimens provided before treatment. Researchers tested whether auto-FMT positively impacted white blood cell counts of the patients as they recovered. Those who received the auto-FMT had higher counts of each type of white blood cells compared to those who did not. The results could stem from having a more complex microbiota, demonstrating that restoring the gut microbiome may aid in restoring the immune system.

To further assess whether this relationship was causal, the researchers used observational data to compare the gut bacterial makeup from stool samples and white blood cell counts of more patients. They found that higher levels of certain bacteria genera, including Faecalibacterium, Ruminococcus and Akkermansia (common commensal bacteria), were associated with higher levels of neutrophil (a type of white blood cell used as a marker for immune health), while those with higher levels of the more pathogenic genera Rothia and Clostridium were associated with reduced neutrophil counts.

Although the development of the gut microbiome at an early age remains key to developing a strong immune system, alterations to the gut microbiome at any point may positively or negatively influence immune health. Many actions support a strong immune system; therefore, paying attention to the gut microbiome may be one key step toward ensuring an efficient immune response.

By Kendra Whitmire, MS, CNS