Four- to six-week-old mice were used to isolate the primary hepatocytes

ocesses and, more directly, by eroding Vonoprazan cartilage. A cell surface marker that defines FLS is CD55. The presence of CD55 in the intimal lining was initially reported by Medof et al.. Later work by Stevens et al. and Edwards and Wilkinson identified CD55 as a marker with an apparent specificity for intimal fibroblasts in synovial disease. CD55, also known as decay-accelerating factor, is a broadly expressed cell surface molecule that protects cells from self-inflicted damage mediated by complement activation. CD55 controls complement by accelerating the decay of C3/C5 convertases. In line with this well-established function, CD55-deficient mice develop increased complement-mediated autoimmunity in a variety of antibody-driven models. Next to its role as a complement regulator, CD55 is a binding partner of CD97, an adhesion-type G protein-coupled receptor abundantly expressed on almost all leukocytes. AdhesionGPCRs are nonclassical heptahelical receptors that facilitate cell and matrix interactions of various cell types. CD97-positive macrophages closely associate with CD55-expressing FLS in the synovial intima. Using CD97-specific multivalent fluorescent probes, we previously demonstrated the ability of CD97 to interact with CD55 on FLS in RA synovium. Based on the sitespecific expression of CD55 and CD97, and the finding that CD97 facilitates leukocyte adhesion in vitro, we postulated that the CD55 Expression on Synovial Fibroblasts interaction of CD97 intimal macrophages with CD55 FLS might facilitate the accumulation of inflammatory cells in the synovial tissue of RA patients. 10455325 Using gene-deficient mice, we recently demonstrated that lack of both CD55 and CD97 indeed ameliorates disease activity in collagen-induced and K/BxN serum transfer models of RA. The high and cell type-specific expression of CD55 raises the question how CD55 expression is triggered in FLS. FLS can be activated by cytokines and molecular patterns, originating from damaged cells, present in the synovial fluid. We therefore tested the ability of a range of pro-inflammatory cytokines and Toll-like receptor ligands to induce CD55 expression in cultured FLS. We show that CD55 was strongly upregulated by triggering of TLR3, an endosomal pattern recognition receptor involved in the detection of double-stranded RNA. Stimulation of the cytoplasmic dsRNA sensors melanoma differentiationassociated gene 5 and retinoic acid-inducible gene-I induced CD55 expression as well. Notably, activation of MDA5, but hardly TLR3 or RIG-I triggering, caused cell death in cultured FLS. Finally, we show that TLR3 activation enhanced the binding of CD97-loaded beads in FLS in a CD55-dependent manner, suggesting that dsRNA increases the interaction of FLS with CD97-positive leukocytes. in Dulbecco’s Eagle’s medium supplemented with 10% heat inactivated fetal calf serum, L-glutamine, HEPES, and antibiotics . Non-adherent cells were removed after 24 h, and adhering cells were grown to sub-confluence and subsequently split by trypsinization. Synovial fibroblasts were used for experiments from passage 3 until passage 9; “8887974 at that time cultures were free of macrophages and non-fibroblasts. Primary dermal fibroblasts, obtained from biopsy samples of normal skin, were kindly provided by Dr. Marcel Teunissen. The cells were cultured in Ham’s F-12 medium with 10% FCS and used for experiments between passage 3 and 5. Reagents and Stimulation Assays Synovial and dermal fibroblasts were cultured in 6-well pl