Regulation of synoviocyte phospholipase A(2) and cyclooxygenase 2 by macrophage migration inhibitory factor

Objective. Macrophage migration inhibitory factor (MIF) is a proinflammator y cytokine with known actions in macrophage and T cell activation. MIF also has the unique capacity to reverse the inhibitory effects of glucocorticoi ds on these cells. We have recently demonstrated MIF expression in human rh eumatoid arthritis (RA) synovium and cultured fibroblast-like synoviocytes (FLS), as well as the ability of FLS-derived MIF to induce monocyte release of tumor necrosis factor alpha. We investigated the effects of MIF on aspe cts of RA FLS activation, including the induction of phospholipase A(2) (PL A(2)) and cyclooxygenase (COX). Methods. PLA(2) activity was measured by H-3-arachidonic acid released from treated FLS supernatants. COX activity was measured by prostaglandin E-2 e nzyme-linked immunosorbent assay. Cytosolic PLA(2) (cPLA(2)) and COX-2 mess enger RNA (mRNA) were determined using semiquantitative reverse transcripta se-polymerase chain reaction. Results. Constitutive PLA(2) activity was detected in RA FLS. Recombinant h uman MIF up-regulated PLA(2) activity (P < 0.01) and cPLA(2) mRNA expressio n, but had no effect on secretory PLA(2). Recombinant human MIF up-regulate d COX activity (P < 0.05) and COX-2 mRNA, but had no observable effect on C OX-1. Interteukin-1 beta (IL-1 beta) significantly up-regulated PLA(2) acti vity (P < 0.005) and cPLA(2) mRNA expression while anti-MIF monoclonal anti body (mAb) significantly inhibited this IL-1<beta>-induced PLA(2) activity (P < 0.02). Anti-MIF mAb significantly reduced IL-1<beta>-induced COX activ ity (P < 0.05) and COX-2 mRNA expression. Conclusion. MIF exerts a proinflammatory effect on key aspects of RA FLS ac tivation. That anti-MIF mAb inhibited IL-1<beta> up-regulation of FLS indic ates an additional cofactor role for MIF in IL-1 beta -induced FLS activati on. These data suggest that MIF antagonism has important therapeutic potent ial in RA.