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Isolated B cells from normal subjects and patients with systemic lupus erythematosus (SLE) could be stimulated to produce IgM anti-DNA with pokeweed mitogen. Normal but not SLE allogeneic T cells abrogated this response. Normal but not SLE autologous T cells promoted a switch from IgM to IgG anti-DNA production. SLE is characterized by at least two types of immunoregulatory abnormalities: a defect in T suppressor function and a defect in the IgM to IgG switchover.

Forty-seven patients with systemic lupus erythematosus were studied to determine the presence of IgM and IgG anticardiolipin antibodies and their association with clinical syndromes. Eleven (23.4%) of the patients had IgG anticardiolipin antibodies; four of these also had IgM anticardiolipin antibodies. The cardiolipin-positive group had significantly lower platelet counts, but no increased history of thrombosis was observed. The anticardiolipin activity of seven of the 11 sera could be decreased by preincubation with DNA, providing confirmatory evidence that anticardiolipin activity actually resides in some populations of anti-DNA.