Background/Purpose:

Recently, we 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 IL-17A production results in a pro-inflammatory loop, which is characterized by an up-regulation in pro-inflammatory cytokines and cartilage degrading enzymes. The 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. The objective of this study is to investigate the mechanism responsible for the autocrine IL-17A induction upon Th17-RASF interaction.

Methods:

CD4+CD45RO+CCR6+ (Th17) and CD4+CD45RO+CCR6- (Th1) cells were isolated by fluorescence-activated cell sorting (FACS) sorting from healthy controls and early RA patients. These cells were co-cultured with RASF, in the presence of neutralizing 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 enzyme-linked immunosorbent assay (ELISA).

Results:

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 quantitative polymerase chain reaction (Q-PCR), respectively. Since IL-1β and IL-6 may be involved in IL-17/Th17 polarization we examined the contribution of these cytokines on the autocrine IL-17A loop. Blockade of IL-1β and IL-6 significantly suppressed IL-17 production. However the effects of IL-1β and IL-6 blockade were limited, indicating the requirement of an additional mechanism.

Interestingly, the genes encoding for cyclo-oxygenase-2 (COX-2) and prostaglandin-E-synthase (PTGES), which are involved in prostaglandin-E₂ (PGE₂) synthesis, were also up-regulated in Th17-RASF cultures. This was associated with a dramatic increase of PGE₂ production in Th17-RASF cultures compared to Th1-RASF cultures. Treatment of Th17-RASF cultures with celecoxib, a COX-2 inhibiter, resulted in significant and specific inhibition of the fraction of IL-17A producing cells and the IL-17A levels. No inhibitory effects were found on IFN-γ and TNF-α production. Moreover, celecoxib treatment functionally inhibited the pro-inflammatory loop as production of the pro-inflammatory mediators IL-6 and IL-8 and tissue destructive enzymes MMP-1 and MMP-3 were significantly suppressed.

Conclusion:

These findings show the critical role of the COX/PGE₂ 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.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-cyclooxygenaseprostaglandin-e2-pathway-is-critical-for-autocrine-il-17a-production-by-th17-cells-upon-synovial-fibroblast-interaction/