IgA synthesis: a form of functional immune adaptation extending beyond gut

► IgA, by promoting microbial diversity in the gut, is likely to have played a fundamental role in mammalian evolution. ► The IgA system fulfils multiple functions in order to maintain homeostasis at mucosal surface. ► IgA regulates the intestinal microbiota that is pivotal for efficient immune system and metabolic function. ► Defects in IgA regulation have the potential to increase autoimmune susceptibility beyond mucosal surfaces.