Platelet-derived growth factor and IL-1 interactions in rheumatoid arthritis. Regulation of synoviocyte proliferation, prostaglandin production, and collagenase transcription.

We show that platelet-derived growth factor (PDGF) and IL-1 interact in both a synergistic and antagonistic manner to regulate synovial fibroblast-like cells (synoviocytes) derived from patients with rheumatoid arthritis. PDGF and IL-1 operated synergistically in vitro to stimulate synoviocyte proliferation in the presence of indomethacin. However, when these same cells were treated with PDGF and IL-1 in the absence of indomethacin, IL-1 inhibited PDGF-stimulated synoviocyte proliferation. Moreover, exogenous PGE2, a PG known to be produced in response to IL-1, dramatically inhibited synoviocyte proliferation induced by PDGF. PDGF also acted synergistically to markedly increase production of PGE2 stimulated by IL-1. This is in contrast to the antagonistic effect PDGF had on IL-1-stimulated collagenase transcription. IL-1 stimulated collagenase transcription, but PDGF did not. It in fact inhibited IL-1 stimulation of collagenase gene expression. These data differ somewhat from those reported for dermal fibroblasts. Our data further indicate that the effects of cytokines vary from one cell type to another, even amongst "fibroblasts," and illustrate the complexity of cytokine regulation of rheumatoid synoviocyte function.