Cell-cell interactions in the rheumatoid joint.

Although rheumatoid synovium has been extensively studied in organ culture, particularly with respect to the synthesis of prostaglandins and proteinases, the behaviour of normal human synovium in culture has been much less well characterized. In this study, cultures of fragments of normal synovial tissue produced significantly less prostaglandin E (PGE) than cultures of rheumatoid synovium. The difference, however, did not persist when synovial cells obtained by enzymatic dispersion of normal and rheumatoid tissue were compared in monolayer culture. Production of PGE could be reactivated in both normal and rheumatoid synovial cells by products of mononuclear blood cells and also by factors in culture medium obtained after incubation of fragments of either normal or rheumatoid synovial tissue. These products of mononuclear cells and of synovial tissue also stimulated the production of PGE by human articular chondrocytes in monolayer culture. If these types of cellular interactions observed in vitro also occur in the arthritic joint as a result of the failure of normal control mechanisms, they could play a part in the irreversible destruction of joint structures.