Previous analyses of Th17 in human inflamed synovial tissues and blood as well as measurements of IL-17 levels in synovial fluid [24,27,40] and seruum [29,33,41], have provided disparate results which still do not allow unequivocal conclusions on the cellular source and pathogenetic role of IL-17 in human RA. Here, IL17A is linked to rheumatoid arthritis.