PRODUCTION OF MONOCYTE CHEMOTACTIC PROTEIN-1 IN HUMAN TYPE-B SYNOVIOCYTES - SYNERGISTIC EFFECT OF TUMOR-NECROSIS-FACTOR-ALPHA AND INTERFERON-GAMMA

Objective. Since local secretion of chemotactic factors could contribute substantially to the homing of monocytes to the rheumatoid synovium, we investigated the ability of type B, or ''fibroblast-like,'' synoviocytes isolated from the synovial tissue of patients with rheumatoid arthritis to synthesize and secrete the novel cytokine monocyte chemotactic protein 1 (MCP-1). Methods. Synthesis and secretion of MCP-1 was determined by immunoprecipitation following metabolic labeling of MCP-1 with S-35-cysteine. MCP-1 gene regulation was assessed by Northern blot analysis. Results. Unstimulated type B synoviocytes released little or no MCP-1, although low levels of MCP-1 messenger RNA (mRNA) were detected. However, incubation of these cells with tumor necrosis factor a (TNFalpha) resulted in a time- and dose-dependent release of MCP-1 into the supernatant, and expression of MCP-1 mRNA. Use of cycloheximide and actinomycin D confirmed that TNFalpha was inducing MCP-1 expression at both the transcriptional and translational levels. Treatment of the synoviocytes with interferon-gamma (IFNgamma) also stimulated an increase in both the steady-state levels of MCP-1 mRNA, as well as MCP-1 protein synthesis and secretion. In addition, TNFalpha and IFNgamma in combination exerted a synergistic effect on both MCP-1 mRNA accumulation and protein secretion. Conclusion. These studies demonstrate that the MCP-1 gene is regulated by TNFalpha and IFNgamma in type B synoviocytes and indicate that these cells may play an important role in the recruitment of inflammatory cells to the rheumatoid synovial environment, via the production of novel chemotactic cytokines such as MCP-1.