Th17 cells in the pathogenesis of rheumatoid arthritis

Naive CD4+ T cells, upon activation by antigen-presenting cells (APCs) and several cytokines, differentiate into different lineages of effector Th subtypes, which play a central role in modulating immune responses. While Th1 and Th2 cells participate in regulation in cellular and humoral immunity, Th17 cells have been identified as a Th subpopulation that regulates inflammatory processes via production of distinct cytokines such as IL-17. The major feature of this subpopulation is involvement in protection against infection caused by microorganisms, and in the pathogenesis of autoimmune diseases and allergy. The role of Th17 cells and IL-17 in various stages of the inflammatory process in rheumatoid joints remains poorly understood and still needs further studies. In this review, we summarize the latest discoveries about phenotype, differentiation and biological function of human Th17 cells, and also their role in the pathogenesis of rheumatoid arthritis.