The COX/prostaglandin-E2 pathway is critical for autocrine IL-17A production by TH17 cells upon synovial fibroblast interaction
Authors: Sandra M J Paulissen, Jan Piet van Hamburg, Nadine Davelaar, Patrick S Asmawidjaja, Johanna M W Hazes, Erik Lubberts
Journal: Annals of the Rheumatic Diseases (2012)

<h3>Backgroundand objectives</h3> Recently, the authors have shown that Th17, but not Th1 cells, from patients with early rheumatoid arthritis (RA) are potent activators of RA synovial fibroblasts (RASF) resulting in autocrine IL-17A production. This autocrine IL-17A production by Th17 cells is critical for the perseverance of the pro-inflammatory loop, but the mechanism underlying the autocrine IL-17A induction is unclear. <h3>Objective</h3> To investigate the mechanism responsible for the autocrine IL-17A induction upon Th17-RASF interaction. <h3>Materials and methods</h3> CD4+CD45RO+CCR6+ (Th17) and CD4+CD45RO+CCR6- (Th1) cells were isolated by FACS sorting from healthy controls and early RA patients. These cells were co-cultured with RASF, in the presence of neutralising antibodies directed against soluble IL-6R (anti-sIL-6R) and/or IL-1β, and celecoxib. Gene expression profiles were generated and supernatant was collected for cytokine analyses by ELISA. <h3>Results</h3> Gene expression analyses revealed that the genes encoding for IL-6 and IL-1β were up-regulated in Th17-RASF cultures. These data were confirmed by ELISA and Q-PCR, respectively. Since IL-1β and IL-6 may be involved in IL-17/Th17 polarisation the authors examined the contribution of these cytokines on the autocrine IL-17A loop. Blockade of IL-1β and IL-6 activity, but not TNFα significantly suppressed IL-17A production in the co-culture, but the inhibitory effects were limited. Of note, the combination of anti-IL-1β and anti-sIL-6R markedly suppressed IL-17F. No effects were found on IFNγ. Interestingly, the genes encoding for cyclo-oxygenase-2 (COX-2) and prostaglandin-E-synthase (PTGES), which are involved in prostaglandin-E<sub>2</sub> (PGE<sub>2</sub>) synthesis, were also up-regulated in Th17-RASF cultures. This was associated with a dramatic increase of PGE<sub>2</sub> production in Th17-RASF cultures compared to Th1-RASF cultures. Treatment of Th17-RASF cultures with celecoxib, an inhibitor of cyclo-oxygenase-2 (COX-2) activity, resulted in a significant decrease of IL-17A, but not of IFNγ and TNFα production. Furthermore, the decrease in IL-17A production caused by celecoxib treatment was much more pronounced compared to neutralising IL-1 and IL-6 activity. Flow cytometry revealed a decrease in Th17 cells in celecoxib treated co-cultures, while no effects on Th1 or Th2 cells were found. Moreover, celecoxib treatment significantly inhibited the pro-inflammatory loop as less induction of IL-6, IL-8 and matrix metalloproteinase-3 production was observed in the Th17-RASF co-cultures. <h3>Conclusions</h3> These findings show the critical role of the COX/PGE<sub>2</sub> pathway in the autocrine IL-17A production upon Th17 and synovial fibroblast interaction. Inhibition of this pathway down-regulates the pro-inflammatory feedback loop induced by Th17-RASF interaction leading to less production of pro-inflammatory cytokines and destructive mediators.