Fibrin(ogen)-induced expression of ICAM-1 and chemokines in human synovial fibroblasts

It has long been recognized that in most inflamed arthritic joints the coagulation system is activated, leading to the local generation of fibrin, and it has long been hypothesized that the local fibrin deposition promotes inflammation and tissue destruction. However, only recently has the direct effect of fibrin on the inflammatory process been seriously investigated, and specific roles assigned to fibrin or its products as mediators of the inflammatory process. Although fibrin and/or fibrinogen (fibrin(ogen)) is abundantly present in inflamed tissues and joints rich in fibroblastic cells, no significant data on fibrin(ogen)-induced gene expression by fibroblasts have been published. We now demonstrate that coculture of human synovial fibroblasts with fibrin(ogen) results in the up-regulation of ICAM-1 as well as increased production of the chemokines IL-8 and growth-related oncogene-alpha. Increased ICAM-1 expression was fibrin(ogen) dose-dependent and was demonstrated by ELISA, flow cytometry, and functional adhesion assays. Levels of ICAM-1 induced by fibrin(ogen) were comparable to those that could be induced by cytokine stimulation. Fibrin(ogen) stimulation of ICAM-1 could be suppressed by pyrrolidinedithiocarbamate, an inhibitor of NF-kappaB activation. Chemokine production was induced by fibrin(ogen) in cell culture supernatants >100-fold as compared with controls. Thus, through its activation of synovial fibroblasts, fibrin(ogen) deposition may promote the recruitment (via chemokines) and retention (via adhesion molecules) of lymphocytes within the arthritic joint.