Role of cytokines in inflammatory synovitis

This study was undertaken in an effort to understand the role of cytokines in T lymphocyte trafficking into inflamed synovium and in the potential enhancement of antigen presentation by human synovial fibroblasts. We found that interleukin‐1β (IL‐1β), tumor necrosis factor α (TNFα), and interferon‐γ (IFNγ) each increased the cell surface expression of intercellular adhesion molecule 1 (ICAM‐1) on human synovial fibroblasts in a dose‐ and time‐dependent manner. Maximal ICAM‐1 expression occurred within 8 hours of induction, with the following order of efficacy: IFNγ > TNFα > IL‐1β. The number of cells bearing the ICAM‐1 antigen also increased, from a basal level of ∼30% to more than 83% after cytokine induction (for all 3 cytokines). ICAM‐1 expression rapidly decreased following cytokine removal. The expression of lymphocyte function‐associated antigen 3 was also examined, but it was not changed by any of the 3 cytokines. Class I major histocompatibility complex antigen expression was increased modestly by all 3 cytokines, and expression was maximal by 24 hours after treatment. Only IFNγ induced HLA class II antigen expression, and this expression persisted for up to 6 days following removal of the lymphokine. IL‐6 and granulocyte‐macrophage colony‐stimulating factor had no effect on any of the parameters examined. Our data support an interactive role for inflammatory cytokines and the expression of adhesion ligands and HLA antigens by human synovial fibroblasts in the pathogenesis of synovial inflammation in rheumatoid arthritis.