IL-22 Produced by T helper Cell 22 as a New player in the Pathogenesis of Immune Thrombocytopenia

Idiopathic thrombocytopenic purpura (ITP) as an autoimmune disease is identified by low count platelet due to decreaed platelet production as well as increased platelet destruction by autoimmune mechanisms in which platelet autoantigen(s) react with the patient's immune system. In ITP a shift toward B cells producing autoantibodies together with CD4+ T helper cells have been reported. T helper cell 22 (Th22) as a new subset of CD4+ T cells is distinctly apart from Th17 and other known CD4+ T cell subsets due to the expression of its specific gene and function. Th22 subset show chemokine receptor CCR4+ CCR6+ CCR10+ phenotype and its key transcription factor is aryl hydrocarbon receptor (AHR). In addition, Th22 cells can be recognized by secretion of a distinguished profile of effector cytokines, including interleukin (IL)- 22, IL- 13, and tumor necrosis factor-α (TNF-α). The amount of Th22 and IL-22 is increased in several autoimmune disorders and positively related to disease severity. The purpose of the present review is to discuss the role of Th22 and its cytokine IL-22 in the immunopathogenesis of ITP.