Augmented numbers of HLA-DR-positive T lymphocytes in the synovial fluid and synovial tissue of patients with rheumatoid arthritis and juvenile rheumatoid arthritis: in vivo-activated T lymphocytes are potent stimulators in the mixed lymphocyte reaction.

Twenty to 40% of T cells from synovial fluid and synovial tissue and 3-11% of the peripheral blood T lymphocytes from patients with rheumatoid arthritis (RA) and juvenile rheumatoid arthritis (JRA) expressed HLA-DR antigens as detected by monoclonal anti-HLA-DR antibodies in direct immunofluorescence. Synovial fluid and synovial tissue T lymphocytes had a stimulating capacity comparable to that of non-T cells in the allogeneic primary mixed lymphocyte reaction (MLR). The MLR was inhibited by monoclonal anti-HLA-DR antibodies. This is, to our knowledge, the first report on in-vivo-activated T lymphocytes as stimulator cells in MLR. The results suggest that T cells from synovial fluid and synovial tissue are locally activated by stimuli so far unidentified.