Rheumatoid synovial dendritic cells as stimulators in allogeneic and autologous mixed leukocyte reactions--comparison with autologous monocytes as stimulator cells.

Dendritic cells were isolated from peripheral blood, synovial fluid, and synovial tissue of patients with rheumatoid arthritis and from peripheral blood of healthy blood donors on the basis of semiadherence to plastic surfaces. The cells were compared with autologous peripheral blood monocytes with respect to their stimulating capacities in allogeneic and autologous mixed leukocyte reactions (MLR). Dendritic cells from the various compartments stimulated allogeneic T cells 6-14 times more than monocytes did. Dendritic cells also stimulated autologous T cells 10-24 times more than monocytes did. Evidence in favour of the dendritic cell as the major stimulating cell type in MLR was also found in mixed experiments in which various ratios of dendritic cells and monocytes were used as stimulator cells. Furthermore, the activating structures on the dendritic cells seem to be major histocompatibility complex class II antigens, since anti-HLA-DR antibodies inhibited the responses. The results, especially from the autologous MLR, indicate that dendritic cells are important accessory cells for the various immune responses in rheumatoid inflammation.