No abstract

No abstract

Rheumatoid arthritis (RA) is a chronic inflammatory disease leading to joint destruction. Cytokines play a key role in its pathogenesis. They contribute to the induction and maintenance of inflammation and thus provide therapeutic targets. Many cytokines are involved in RA, and this review focuses on a few critical ones: tumor necrosis factor (TNF), interleukin (IL)-6, IL-1, IL-17, and GM-CSF. TNF and IL-6 are both well-established targets in RA treatment, and new biologic agents are reaching the market. IL-1 represents a more complex cytokine as results in humans do not reach those in animal models. IL-17 and GM-CSF are cytokines representing new targets either as early treatment or in non-responders to other biologics. The interaction between cytokines and their signaling pathways are the basis for the development of new strategies with small molecules or bispecific antibodies. Clearly, the targeting of cytokines has been a major progress in RA treatment, but many issues remain open. Although remission can be better achieved, reactivation of the disease too often occurs upon treatment discontinuation. Better understanding and targeting of chronicity remains a goal to achieve in the future.

BackgroundDuring chronic inflammation, immune cells, notably Th17 cells, infiltrate the inflammatory site and interact with local mesenchymal cells. Applied to rheumatoid arthritis (RA), the aim is to study the interactions between synoviocytes and peripheral blood mononuclear cells (PBMC) with a focus on the Th17 pathway and to identify a mechanism which leads to high IL-17 secretion with an interest on podoplanin.MethodsPBMC from healthy donors and RA patients were co-cultured with RA synoviocytes during 48 h, in the presence or not of phytohemagglutinin. An antibody against podoplanin was used in co-culture. Cytokine production (IL-6, IL-1β and IL-17) was measured by ELISA and cell staining (CD3, CD4, IL-17 and podoplanin) by flow cytometry.ResultsIn control conditions, IL-6 and IL-1β production was increased in PBMC-synoviocyte co-culture compared to PBMC alone (p = 0.02). No additional effect was observed with PBMC activation. Flow cytometry analysis showed no difference in the percentage of Th17 cells in activated PBMC alone or with synoviocytes (p = 0.4), indicating that Th17 differentiation requires only T cell activation. Conversely, IL-17 production was highly increased in co-cultures with activated PBMC vs. activated PBMC alone (p = 0.002). Transwell experiments confirm that cell-cell contact was critical for IL-17 secretion. The incubation of either PBMC or synoviocytes with an anti-podoplanin antibody decreased IL-17 secretion by 60 % (p = 0.008).ConclusionsInteractions between resting PBMC and synoviocytes are sufficient to induce IL-6 and IL-1β production. Both PBMC activation and cell interactions are needed to induce a high IL-17 secretion. Podoplanin contributes at the level of both lymphocytes and synoviocytes.