The Gut Microbiome in Health and in Disease

Andrew B. Shreiner; John Y. Kao; Vincent B. Young


Curr Opin Gastroenterol. 2015;31(1):69-75. 

In This Article

Host–microbe Interactions on the Immune System

Interactions between the microbiota and the host immune system are numerous, complex, and bidirectional. The immune system must learn to tolerate the commensal microbiota and respond appropriately to pathogens, and, in turn, the microbiota is integral to educating the immune system to function properly. Here, we highlight studies that describe how members of the microbial community promote the differentiation of anti-inflammatory regulatory T cells (Treg) to illustrate how the microbiota can influence immune homeostasis. A series of experiments showed that collections of nonpathogenic species of Clostridia from clusters IV, XIVa and XVIII, isolated after application of a series of nonspecific selection steps, were capable of inducing colonic Treg, and one mechanism may involve the production of butyrate that affects epigenetic control of the Foxp3 promoter that controls Treg development.[17,18,19–22] In germ-free mice that do not contain endogenous microbiota, another group also devised a novel method to screen human fecal samples for bacterial strains able to promote Treg development, and they noted this functional capacity in more strains than anticipated.[23] Although not discussed here, there is evidence detailing host–microbe interactions that influence immune functions at all levels from the initial innate defenses to the complex acquired responses discussed in this section.[24] There is great interest in elucidating how the microbiota can influence immune homeostasis inside and outside the gut, as this process has important implications for the pathogenesis and treatment of inflammatory disorders and a growing list of diseases linked to inflammation.