Abstract

The constituents of the commensal microbiota that inhabit our intestine have co-evolved with us for mutual benefit. They regulate maturation of gut lymphoid tissues and the balance of pro- and anti-inflammatory intestinal lymphocytes.

Lymphocytes that produce the cytokines IL-17 and IL-22 protect mucosal surfaces from damage inflicted by bacteria and fungi, but also have critical roles in multiple autoimmune diseases and in inflammatory processes that impact diseases ranging from asthma to atherosclerosis and cancer. Most prominent among these lymphocytes are the Th17 cells, a subset of CD4 + T-helper cells that mediate autoimmunity in mice and humans. Disruption of the balance between Th17 and anti-inflammatory regulatory T cells, which is governed by signals from distinct commensal microbes, can predispose to autoimmune diseases that affect distal organs. Inflammatory lymphoid cells share a genetic program dependent on expression of the orphan nuclear receptor RORgt, a promising target for anti-inflammatory therapy.

A genomic analysis of the Th17 cell transcriptional regulatory network is being used to identify additional key factors required for Th17-mediated inflammation and to uncover new therapeutic targets in autoimmune disease. Microbiota-induced Th17 cells of unknown specificity can mediate autoimmune disease at distal sites. These results have inspired studies of the gut microbiome in human autoimmune disease, revealing an association of specific commensal bacteria with new onset rheumatoid arthritis.