Research & Education

How the Immune System Helps Balance Gut Bacteria

The microbiome and the immune system dance to a delicate tune for optimal balance in a bi-directional, symbiotic relationship. One of the key sites for this interaction takes place in the gut, which is one of the places where the human body interacts with the environment. Food and beverage consumption increase the chances of encountering pathogens, toxins, and other disease-promoting substances.

Although the commensal bacteria help fight against potential invaders, the immune system plays a key role in maintaining a balanced gut microbiome by weeding out the pathogenic microbes while allowing the commensal bacteria and other microbes to remain in residence. Because of the importance of the immune system’s gut health, there is a dedicated system in place: the gut-associated lymphoid tissue (GALT).

The gastrointestinal system’s GALT is considered another organ that makes up the largest peripheral immune tissue in the body with an estimated 60% to 70% of peripheral lymphocytes. The GALT has complex mechanisms and systems in place to recognize commensal bacteria so they will not be attacked while launching an attack against perceived threats from other harmful bacteria.

Key components of the gut’s response to pathogens include mucosal and epithelial layers of the intestines for a physical barrier, additional specialized cells that secrete antimicrobial proteins, and a special epithelial cell known as microfold cells (M cells) that sense luminal bacteria to signal the GALT to induce secretory immunoglobulin A (IgA) for containment. Secretory IgA is the most important and abundant antibody class in the lumen and plays a key role in the initial immune defense to block access and adherence of the pathogenic bacteria among other actions. Once the antigen is recognized, then the innate and adaptive immune responses are appropriately triggered.

A recent study found that GALT antibody production toward the gut microbiome may be more advanced than previously believed. Rather than a broad-spectrum approach, the immune system develops a targeted attack toward potentially pathogenic microbes to maintain a balanced microbiome. In the GALT, there are germinal centers where B cells learn antibodies, and one “winner” cell effectively recognizes the target and is replicated to do its magic, which is designed to attack specific bacterial species.

Rather than occurring only when there is an infection (as with other parts of the immune system), the cloning practice of this antibody continually transpires in the GALT. The speed and types of antibodies are dependent on the makeup of the microbiome. In the same recent study just referred to above, mice that had a balanced microbiome rarely underwent the process. However, germ-free mice did undergo the antibody process at much higher rates. This may be one way that GALT aids in maintaining a balanced microbiome.

Our knowledge of the complex relationship between the gut microbiome and the human immune system remains in its early stages, with more research necessary to fully elucidate the interactions and relationships. However, we do know that maintaining a balanced gut microbiome and sufficient levels of secretory IgA benefits overall wellness and immune health. Consuming a healthy diet with the right types of fiber, along with additional support, such as prebiotics and probiotics, are some of the key steps to sustain a balanced gut microbiome.

By Kendra Whitmire, MS, CNS