Abstract
IL-17A is implicated in rheumatoid arthritis (RA) pathogenesis; however, the contribution of IL-17F remains to be clarified. Using microarrays and gene-specific expression assays, we compared the regulatory effects of IL-17A and IL-17F alone or in combination with TNF-alpha on RA synoviocytes. IL-17A and IL-17F expression was studied in osteoarthritis and RA synovium by immunohistochemistry. The comparison between the IL-17A and IL-17F stimulatory effect on RA synoviocytes was assessed at the protein level by ELISA and at the mRNA level by microarrays and real-time RT-PCR. TNFRII expression was studied by real-time RT-PCR and immunofluorescence, and neutralizing Ab was used to analyze its contribution to CCL20 secretion. IL-17A and IL-17F were detected in plasma cell-like cells from RA but not osteoarthritis synovium. In microarrays, IL-17A and IL-17F alone had similar regulatory effects, IL-17F being quantitatively less active. Both cytokines induced a similar expression pattern in the presence of TNF-alpha. Based on a cooperation index, 130 and 203 genes were synergistically induced by IL-17A or IL-17F plus TNF-alpha, respectively. Among these, the new target genes CXCR4, LPL, and IL-32 were validated by real-time RT-PCR. IL-17A and IL-17F up-regulated TNFRII expression, but had no effects on TNFRI, IL-17RA or IL-17RC. TNFRII blockade inhibited the synergistic induction of CCL20 by IL-17A or IL-17F and TNF-alpha. IL-17A and IL-17F are both expressed in RA synovium. In the presence of TNF-alpha, they induced a similar expression pattern in RA synoviocytes. Accordingly, IL-17F appears as a target in Th17-mediated diseases such as RA.