Immunocytology of synovial fluid cells may be of diagnostic and prognostic value in arthritis.

Cells of the synovial fluid (SF) have been examined by immunocytochemical methods. Samples were aspirated from four groups of patients with knee effusions: (a) seropositive inflammatory arthritis (n = 9); (b) seronegative inflammatory arthritis (n = 9); (c) osteoarthritic patients (n = 5); and (d) patients with traumatised knees (n = 4). The proportions of lymphocyte and macrophage subsets within the SF were determined with a panel of monoclonal antibodies. Patients with inflammatory arthritis had significantly larger proportions of activated T cells (RFT2+) and macrophages with the phenotype of interdigitating cells (RFD1+). No significant difference between groups could be found on differential count or when T4+/T8+ subset ratios were calculated. No significant difference in proportions of lymphocyte or macrophage subsets was found between the groups with seropositive and seronegative inflammatory arthritis. In two of three patients, where immunocytochemical analysis was performed before and after intra-articular steroids, reductions in the proportions of RFT2+ T cells and RFD1+ macrophage like cells were seen. It is suggested that such analysis may be of diagnostic or prognostic value.