Interactions between the gut and the immune system 3rd in a series

THE INTERACTIONS BETWEEN THE GUT AND THE IMMUNE SYSTEM

By Don Pearson, Technical Director, BioBrew Ltd

The immune system is a series of cells and molecules that protect us from disease. It does this by responding to any foreign substances they register as threats, especially infectious microbes. Our immune system has co-evolved with our diverse gut flora. It can create defences against pathogens and also develop tolerances for beneficial microbes (Ley et. al., 2006). The importance of this interaction is highlighted by the fact that 70–80% of the body’s immune cells are found in the gut (Wu and Wu, 2012)

The conversation between the immune system and the microbiome starts when our bodies first come in contact with microbes, at birth, though the is some evidence that it occurs in the womb (Walker et. al., 2017). The environment at birth is important for the inoculation of the new-born with microbes. Human milk contains a range of carbohydrates that cannot be used by the baby. These selectively feed good gut microbes especially beneficial Bifidobacteriumspecies (Centanni et. al., 2019). The microbiome influences the development of our immune system, and the immune system influences the composition of the microbiota (Wu and Wu, 2012). This interaction is maintained throughout life and is one of the keys for a healthy immune system.

When things are going well, the immune system promotes the growth of beneficial microbes that help maintain a stable microbial community. At the same time, a healthy microbiota produces molecular signals that support the development of immune cells and contribute to the fine tuning of immune responses (Wu and Wu, 2012). A healthy interaction between the gut microbiome and the immune system promotes appropriate responses to pathogens (disease causing organisms), promotes tolerance to harmless microbes and their products, and helps maintain self-tolerance (the ability of our immune system to not react harmfully to our own body) (Wu and Wu, 2012).

Our immune system co-evolved with the microbes of our gut. They work synergistically to keep us healthy and protect us against undesirable microbes.

Centanni, M., Ferguson, S. A., Sims, I. M., Biswas, A., Tannock, G. W. 2019. Bifidobacterium bifidum ATCC 15696 and Bifidobacterium breve 24b metabolic interaction based on 2’-O-fucosyl-lactose studied in steady-state cultures in a Freter-style chemostat. Applied and Environmental Microbiology doi:10.1128/AEM.02783-18.

Ley R.E., Peterson D.A., Gordon J.I. (2006) Ecological and Evolutionary Forces Shaping Microbial Diversity in the Human Intestine. Cell 124, 837–848, February 24, Elsevier

Walker, R. W., Clemente, J. C., Peter, I., & Loos, R. (2017). The prenatal gut microbiome: are we colonized with bacteria in utero?. Pediatric obesity, 12 Suppl 1(Suppl 1), 3–17. https://doi.org/10.1111/ijpo.12217

Wu, H. J., & Wu, E. (2012). The role of gut microbiota in immune homeostasis and autoimmunity. Gut microbes, 3(1), 4–14. https://doi.org/10.4161/gmic.19320