Background The relevance of chemokines (CK) in rheumatoid arthritis (RA) has been mainly focused on their chemotactic properties to direct selective migration of leukocytes. However, demonstration of chemokine receptors (CKR) on various non-haematopoietic cells is expanding the knowledge of their roles in biology.
Objectives To explore the presence of CKR and their functional status on cultured fibroblast-like-synoviocytes (FLS) obtained from synovial tissues of RA and osteoarthritis (OA) patients.
Results Flow cytometry analysis with monoclonal antibodies detected expression of CCR2 (MCP-1,2,3 R) on 28 ± 11% FLS, and yielded a wide range of expression of CCR5 (MIP-1a, -1b, RANTES R), CXCR4 (SDF-1a R) and CXCR3 (IP-10, Mig R) on FLS (8–18%) both from RA and OA. CXCR4 mRNA and, to a lower extent, CCR2 mRNA, were detected by RNAse protection assays on RA FLS. To assess the functional ability of these CKR in response to putative ligands we performed assays of CKR engagement that typically lead to pertussis toxin-sensitive PLC activation. After stimulation with CK, FURAred-loaded FLS were screened for changes in cytosolic calcium concentration by measuring related fluorescence changes in a FACScan. SDF-1a induced a significant cytosolic calcium influx, as did positive control stimulation with calcium ionofore A23187. A consistent effect from IP-10 or MCP-1 was not detected.
Assays of synoviocyte chemotaxis using two-compartment trans wells showed significant increments in FLS transmigration induced by SDF-1a (224 ± 134%, p < 0,05) and IP-10 (252 ± 31%, p < 0,05) compared to MCP-1, RANTES, MIP-1b or unstimulated FLS (100%). This enhanced migration could be inhibited in the presence of pertussis toxin (57–77% inhibition).
Conclusion This is, to our knowledge, the first description of the presence of CKR on FLS, notably CXCR4. Our data demonstrate that these receptors are functional as it is shown by CK promotion of both calcium movilization and cell migration. As occurs with leukocytes, CKR could guide synoviocytes through the tissue, likely following a hierarchy of chemotactic signals and therefore, CK might enhance invasive properties of pannus FLS into the cartilage and bone.