Vijay K. Kuchroo

Th17 and Th22 Cells

Th17 cells are a subset of effector CD4 T cells that induce neutrophilic tissue inflammation, particularly in mucosal tissues. While they play a critical role in host defense against extracellular bacteria and fungi, they also have been implicated in the pathogenesis of a number of T cell–mediated autoimmune disorders, including multiple sclerosis, rheumatoid arthritis, and psoriasis. Consistent with their dichotomous roles in promoting host defense and inducing autoimmunity, several subtypes of Th17 cells have been described with distinct effector functions and differing ability to induce autoimmune tissue inflammation. Moreover, Th17 cells are markedly plastic, both in their expression of cytokines typically associated with other effector T cell subsets and in their relationship with regulatory CD4 T cells; and this plasticity has important functional consequences. In this article, we describe the mechanisms that control Th17 cell differentiation, function, and plasticity, as well as highlight Th22 cells, a recently described and closely related CD4 T cell subset.