Microbial Interactions with the Intestinal Epithelium and Beyond: Focusing on Immune Cell Maturation and Homeostasis

Purpose of Review: Our perception of human microbes has changed greatly in the past decade from a focus on pathogens and infections to a new world view of mutualism and coevolution of microbes and mammalian hosts. This review article seeks to explain the dynamic interactions occurring between the intestinal microbiome and the mammalian host mucosa. Recent Findings: Microbial metabolites influence the functions of epithelial, endothelial, and immune cells in the intestinal mucosa. Microbial metabolites like SCFAs and B complex vitamins influence macrophage differentiation and polarization, whereas microbe-derived biogenic amines such as histamine modulate the biology of the intestinal epithelium and immune responses. Aberrant bacterial lipopolysaccharide-mediated signaling may be involved in the pathogenesis of chronic intestinal inflammation and colorectal carcinogenesis. Summary: We conclude that gut microbes (commensals and probiotics) can have profound impact on mammals by modulation of intestinal immunity and physiology and by influencing the functions of various cell types within the intestine. In addition, microbial metabolites have well-defined effects on shaping the gut epithelium, and these compounds play a key role in maintaining intestinal homeostasis. Therefore, effectively manipulating the microbiome via changes in diet and microbial composition and function may yield advances regarding diagnosis and treatment.