Lymphocytes, polymorphonuclear leukocytes, macrophages and platelets in synovium involved by rheumatoid arthritis. A study with monoclonal antibodies.

The inflammatory cell infiltrate involving synovial tissues from joints affected by rheumatoid arthritis (RA)++ has been contrasted with that present in synovium removed from joints involved by previous trauma (T) or osteoarthritis (OA). Cell deployment has been mapped by immunohistochemistry using monoclonal antibodies which recognise epitopes characterising T and B cells, polymorphonuclear leukocytes, mononuclear phagocytes and platelets. Mononuclear phagocytes were the most consistent feature of the rheumatoid inflammatory cell exudate and were present, particularly in the synovial layer, in all OA/T samples. The synovial cells lacked the C3b complement receptor, CR1, but expressed CR3, the receptor for C3bi. In rheumatoid synovium, interdigitating cells were difficult to identify but cells of dendritic morphology bore at least one macrophage epitope. T cells far out-numbered B cells and generally lacked the IL-2 receptor which is an indicator of T cell activation. Care is required in the estimation of the T helper/inducer (TH) T suppressor/cytotoxic (Ts) ratio. Polymorphonuclear leukocytes were demonstrated around vessels and near the synovial intimal cell layer suggesting rapid tissue transit. Extravascular platelets were sparse. Follicular dendritic cells were defined by their central location in lymphoid follicles and strong expression of CR1 receptors. HLA-DR expression was widespread except on endothelial cells.