Fig. 2.

The gut microbiome modulates host immune responses via the gut-brain-immune axis through a variety of mechanisms including microbial community dynamics and circulating microbial products and immune factors. Among these mechanisms, the vagus nerve allows gut microbes to communicate with the brain and modulate the immune system and maintain homeostasis in the host's body. As demonstrated in Poutahidis et al., 2013, vagotomies, which sever this line of communication, block gut-mediated immune modulation affecting the circulation, distribution, activation and potency of various immune cells [10].