Interleukin-21 in T cell-mediated diseases.

Interleukin-21 (IL-21), a cytokine produced by activated CD4+ T cells, activated natural killer T cells, and T follicular cells, has been reported to play a crucial role in the tissue-damaging T cell response in various organs, such as gut, skin, pancreas, and joints. This pathogenic effect is strictly linked to the ability of IL-21 to enhance the functional activities of multiple immune and non-immune cells. Consistently, studies from various laboratories have shown that blockade of IL-21 limits the progression of T cell-mediated inflammatory diseases in mice. Here we review the present knowledge on the expression and role of IL-21 in T cell-mediated pathologies.