[Th17 cells in human rheumatoid arthritis]

Many autoimmune diseases, such as rheumatoid arthritis (RA), have been thought as Th1-mediated diseases. However, recent studies demonstrated critical roles of IL-17, which is produced by a newly identified subset of helper CD4T cells, Th17, in the development of murine models of autoimmune diseases. In addition, many biological functions of IL-17 fit very well with the pathology of RA joints. However, despite the presence of some reports detecting IL-17 in RA joints, the prevalence of Th17 cells in human RA had been largely unknown. Therefore, we analyzed Th17 cells in RA by intracellular staining methods. We found the frequency of IL-17-producing T cells was not increased in RA and was not correlated with disease activity of RA. Surprisingly, the frequency of CD4 T cells capable of IL-17 was decreased in the joints compared with PBL in each individual, whereas Th1 cells predominantly infiltrated in the joints. Taken together with the results of other reports measuring IL-17 production in RA, it seems premature to conclude that IL-17 is abundantly produced in RA joints. Further investigation on the involvement of Th17/IL-17 in human RA is required.