Mucosal Immunity and the Microbiome

Abstract

By definition, the mucosal immune system is responsible for interfacing with the outside world, specifically responding to external threats, of which pathogenic microbes represent a primary challenge. However, it has become apparent that the human host possesses a numerically vast and taxonomically diverse resident microbiota, predominantly in the gut, and also in the airway, genitourinary tract, and skin. The microbiota is generally considered symbiotic, and has been implicated in the regulation of cellular growth, restitution after injury, maintenance of barrier function, and importantly, in the induction, development, and modulation of immune responses. The mucosal immune system uses diverse mechanisms that protect the host from overt pathogens, but necessarily has coevolved to monitor, nurture, and exploit the normal microbiota. As a whole, mucosal immunity encompasses adaptive immune regulation that can involve systemic processes, local tissue-based innate and inflammatory events, intrinsic defenses, and highly conserved cell autonomous cytoprotective responses. Interestingly, specific taxa within the normal microbiota have been implicated in roles shaping specific adaptive, innate, and cell autonomous responses. Taken together, the normal microbiota exerts profound effects on the mucosal immune system, and likely plays key roles in human physiology and disease.

Exercise-induced stress behavior, gut-microbiota-brain axis and diet: a systematic review for athletes

“…Given the gut microbiota’s diverse role in GI function, enteric immunity [70], endocrinology [11] as well as regulating oxidative stress [71–73] and hydration levels, it is not surprising that efforts to identify the mechanisms by which gut microbiota improves intestinal barrier function of elite athletes are increasing.…”

Immune-directed support of rich microbial communities in the gut has ancient roots

“…Complex communities of microbes colonize nearly every epithelial surface of animals, including mucosal epithelial surfaces that become highly valued locales for microbial attachment and growth immediately upon birth (Neish, 2014). The gastrointestinal (GI) system, in particular, has emerged as a prime example of an epithelium-lined organ that sustains an abundant and complex community of closely associated, generally species-specific microbiota, which can exert enormous physiological influence on animal hosts (Savage, 1977; Falk et al, 1998; Neish, 2009; Lozupone et al, 2012; Yatsunenko et al, 2012).…”

Microbial interactions in the fish gut

“…TLR9 was expressed on the colonic apical surface in wild type but not germ-free mice (Ewaschuk et al, 2007). These results demonstrated that the gut microbiota alters the way the host reacts to infectious stimuli or particular bacterial taxa (Neish, 2014) entering the gut, and this difference could also be the case in the present study. Differences in the initial priming of the immune system in the probiotic group are certainly among the potential mechanisms (Thompson et al, 2010;Corthésy et al, 2007).…”