Subset specificity of antilymphocyte antibodies in systemic lupus erythematosus. Preferential reactivity with cells bearing the T4 and autologous erythrocyte receptor phenotypes.

The relative specificity of systemic lupus erythematosus antilymphocyte antibodies for T cell subsets bearing the OKT4, OKT8, or autologous erythrocyte rosette (A-RFC) markers was examined in complement-dependent microcytotoxicity assays and by indirect immunofluorescence. Target cells included normal OKT4+ or OKT8+ T cell clones established from mitogen-activated blasts, resting or phytohemagglutinin-activated peripheral T cells highly enriched for OKT4+ cells or OKT8+ cells, and A-RFC+ and A-RFC- populations. In the majority of sera, cytotoxicity for T4+ cells was greater than that for T8+ cells regardless of cellular activation status. Overall cytotoxicity was considerably higher for activated cells, however, especially when warm assay temperatures were used. A-RFC+ targets were more reactive than nonrosetting T cells, and this was associated with strikingly higher relative fluorescence intensity of IgM staining. Despite these consistent differences in relative cytotoxicity or staining, antibody titers against all cell types were strongly correlated in individual sera. Absorption experiments failed to demonstrate distinct antibody specificities for T4+ and A-RFC+ cells. These data suggest that the major determinant of cytotoxic reactivity may be a single or limited number of surface antigens common to all T cells. Superimposed on this dominant system(s) is a special reactivity with certain distinct subsets and with activated T cells generally.