Immune functions of human synovial cells. Phenotypic and T cell regulatory properties of macrophage-like cells that express HLA-DR.

Normal and rheumatoid synovial cells have been analyzed in frozen sections and in suspension. HLA-DR-expressing, macrophage-like cells are demonstrated in normal synovial intima and in rheumatoid tissue. Suspended normal synoviocytes equaled peripheral blood non-T lymphocytes as stimulators of mixed lymphocyte reactions, whereas adherent rheumatoid synovial cells were extremely efficient as such stimulators and in presenting soluble antigens to autologous T lymphocytes. This HLA-DR-dependent T lymphocyte regulation might provide a cellular basis for the HLA-D haplotype-arthritis associations.