Monocyte chemoattractant protein-1 (MCP-1) in inflammatory joint diseases and its involvement in the cytokine network of rheumatoid synovium

Macrophages infiltrated into synovium play an important role in joint destruction in inflammatory joint diseases. In this study we focused on the production of monocyte chemoattractant protein-1 (MCP-1), a recently identified monocyte chemotactic protein, by inflammatory synovium. Synovial fluid (SF) from rheumatoid arthritis (RA), osteoarthritis, gout, and traumatic arthritis contained MCP-1. MCP-1 was produced in the synovium of patients with RA and other inflammatory joint disease in in vitro culture systems; differences in the amounts produced were not significant. Synovial MCP-1 production in RA was further investigated. Levels of MCP-1 were significantly correlated with levels of IL-1β, IL-6, and IL-8 in the culture supernatants of synovia from RA. Using immunohistochemical techniques, MCP-1 was detected in the lining and sublining cells and in the vascular endothelial cells of rheumatoid synovia. Rheumatoid synovia with active inflammation were stained more intensely by anti-MCP-1 antibody than were those with weak or inactive inflammation. IL-1β and TNF-α stimulated the expression of MCP-1 mRNA and de novo MCP-1 synthesis by cultured synovial cells. These results suggest the production of MCP-1 by synovium of various inflammatory joint diseases. In rheumatoid synovium, a cytokine network involving MCP-1 and other proinflammatory cytokines (IL-1β, IL-6, IL-8, and TNF-α) contributes to the immunopathogenesis of RA.