A serum inhibitor of immune regulation in patients with systemic lupus erythematosus.

Normal mononuclear leukocytes were incubated with serum from patients with active systemic lupus erythematosus (SLE) and healthy subjects and then studied on lymphoproliferative tests. Serum from SLE patients that contained an autoantibody to a subpopulation of thymus-derived (T) lymphocytes inhibited suppressor T-cell activity induced with concanavalin A. These sera did not inhibit lymphoproliferative responses or suppression by monocytoid cells. Mitogen-activated suppressor cells were not inhibited with serum from SLE patients or healthy subjects lacking T-cell autoantibody. This abnormality may contribute to the altered immune response that occurs with SLE.