FIGURE 2.

Changes of the gut microbiota and intestinal mucosal immunity in aging hosts. Proposed mechanism by which aging of the intestinal mucosal immune system leads to gut microbiota dysregulation and immune cell dysfunction. The density and antigen cross‐presentation of intestinal epithelial M cells decrease during aging, which leads to downregulation of antigen intake by dendritic cells and macrophages. Moreover, downregulation of antigen‐presenting cell activated associated cytokines and the quantity of antigen‐presenting cell restrained T cell activation, which reduces the secretion of cytokines, such as IFN‐γ. In turn, these changes reduce the affinity of IgA for antigen and increased the heterogenicity of IgA. In addition, gut microbiota dysregulation characterized by a decrease in beneficial microorganisms and increase in pro‐inflammatory symbionts also occur in the aging host