A Subset of Interleukin-21 + Chemokine Receptor CCR9 + T Helper Cells Target Accessory Organs of the Digestive System in Autoimmunity

This study describes a CD4 + T helper (Th) cell subset marked by coexpression of the cytokine interleukin 21 (IL-21) and the gut-homing chemokine receptor CCR9. Although CCR9 + Th cells were observed in healthy mice and humans, they were enriched in the inflamed pancreas and salivary glands of NOD mice and in the circulation of Sjögren's syndrome patients. CCR9 + Th cells expressed large amounts of IL-21, inducible T cell costimulator (ICOS), and the transcription factors Bcl6 and Maf, and also supported antibody production from B cells, thereby resembling T follicular B helper (Tfh) cells. However, in contrast to Tfh cells, CCR9 + Th cells displayed limited expression of CXCR5 and the targets of CCR9 + Th cells were CD8 + T cells whose responsiveness to IL-21 was necessary for the development of diabetes. Thus, CCR9 + Th cells are a subset of IL-21-producing T helper cells that influence regional specification of autoimmune diseases that affect accessory organs of the digestive system. ► IL-21-producing CCR9 + Th cells are found in the pancreas and salivary gland lesions ► CCR9 + Th cells are increased in the circulation of most Sjögren's syndrome patients ► CCR9 + Th cells, like T follicular helper cells, highly express Bcl-6 ► CCR9 + Th cells provide IL-21 to CD8 + T cells to elicit type 1 diabetes