Fig. 1

The interplay between gut microbiota and host’s immune system. Host’s immune system keeps gut microbiota stable and prevent outgrowth of pathogenic species by production of antimicrobial peptides (AMP) creating a sterility gradient, mucus separating the microbiota from the host, and secretory IgA neutralizing biologically active antigens. Gut microbiota are also important to the generation of optimal immune responses, including triggering differentiation of Th17 and regulatory T cells, driving generation of memory T cells and controlling maturation of NKT cells. MAMPs microbial-associated molecular patterns, IEL intraepithelial lymphocyte, IEC intestinal epithelial cell and Treg T regulatory cell