Antileukocyte antibodies in sera from patients with systemic lupus erythematosus (SLE) were characterized by determining cross-reacting specificities with the antigens defined by OKT3, OKT4, OKT8, OKM1 and anti-Ia hybridoma antibodies (Abs). T cells were prepared by sheep erythrocyte (E) rosetting after removal of adherent cells. T cells, or non-T cells, were preincubated with SLE sera at 4°C and then with monoclonal Abs. Binding by specific monoclonal Abs was assessed by two methods: rosetting with ox erythrocytes conjugated with goat anti-mouse IgG and also in the fluorescence-activated cell sorter using fluorescein isothiocyanate-conjugated goat anti-mouse IgG. Using the rosetting method, we found that sera from SLE can block the binding of monoclonal mouse hybridoma anti-Ia Abs to T cells; the blocking of other monoclonal Abs was not consistent. Using fluorescence-activated cell sorter analysis, preincubation with SLE sera lowered the intensity of staining and total percentage of either T or non-T cells stained by monoclonal anti-Ia Abs. Blocking of anti-Ia Abs binding by SLE sera was not histocompatibility leukocyte antigen (HLA)-DR restricted and was not due to Fc receptor binding. These results indicated that antibodies in SLE sera react with structures contiguous to or identical with Ia determinants. Anti-Ia activities in SLE sera correlate with SLE disease activity. In addition, there was a significant negative correlation between anti-Ia blocking activity in the sera and the percentage of Ia-positive T cells in the blood of SLE patients. Antibodies in SLE sera with anti-Ia blocking activity may play an important role in immune dysregulation in SLE patients.
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