Antigen density on the surface of mononuclear cells in SLE

Searching for the cause of the known immunological abnormalities in systemic lupus erythematosus (SLE), the density of cell surface antigens was measured after immunofluorescent staining in a cell sorter. The densities of CD3, CD4, CD5, CD8 and sIgM lymphocyte antigens were the same on patients' lymphocytes as on lymphocytes from healthy subjects. The intensity of HLA-DR immunofluorescence was found to be decreased on patients' monocytes, while the expression of HLA-DR on lymphocytes of patients with SLE hardly differed from that in healthy subjects. Pretreatment of normal mononuclear cells with patients' sera free from immune complexes decreased the binding of anti-HLA-DR antibody to normal monocytes, but it hardly caused alteration on lymphocytes. After culturing, the expression of HLA-DR antigen on patients' monocytes became the same as on normal cells. A causal role of anti-HLA-DR autoantibodies is suggested and discussed.