The immune barrier. Dendritic cells (DCs) and macrophages patrol the gastrointestinal tract in high numbers. They densely populate the intestinal lamina propria and form a widespread microbe-sensing network. Activated DCs can secrete a number of cytokines and chemokines, including interleukin-23 (IL-23), IL-6, and IL-1, activating IL-23-responsive cells. IL-23-, IL-17-, and IL-22-producing cells are enriched in gut mucosa, and IL-17 and IL-22 are known to be important regulators of intestinal 'health'. IL-17 plays important roles in intestinal homoeostasis in several ways, including maintenance of epithelial barrier tight junctions. LTi, lymphoid tissue inducer; MAIT, mucosa-associated invariant T; NKT, natural killer T; T reg, regulatory T; TNF, tumor necrosis factor.
Costello et al. Arthritis Research & Therapy 2013 15:214 doi:10.1186/ar4228