IgG antilymphocyte antibodies in SLE detected by ¹²⁵I protein A

125I-labeled protein A was utilized to detect lymphocyte binding of IgG at 37 degrees C in 50 sera from patients with SLE. IgG binding was partially inhibited by preincubation of test cells with immune complexes in 50% of sera. In 10%, cytophilic Ig was increased by immune complex preincubation, and in 40% no appreciable change was recorded. With purified preparations of T and B cells, binding of SLE IgG at 37 degrees C was equal for both cell populations.