Suppressor cell function and anti-DNA antibody idiotypes in the serum of SLE patients and their first-degree relatives.

Sixteen-six (16/6) is a major cross-reactive idiotype of monoclonal anti-DNA antibodies, which was derived from the fusion of lymphocytes of a patient with systemic lupus erythematosus (SLE). Antibodies with the 16/6 idiotype (16/6 Id) are increased in the sera of patients with SLE and deposited in their gomeruli and skin. Since stimulated lymphocytes from healthy persons have the capacity to produce 16/6 Id, the mechanisms controlling its expression in health and their possible failure in SLE are of considerable interest. A defect in suppressor cell function was found in a high proportion of patients with SLE and in some of their first-degree relatives. Suppressor cell function in 15 SLE patients and in 53 relatives was compared with the level of 16/6 Id as well as with immunoglobulin levels and anti-DNA antibodies. Ten of 15 SLE patients and 26 of 53 first-degree relatives had increased serum 16/6 levels, which was found in only 1 of 35 healthy controls and household members. Of the 10 SLE patients with increased 16/6, six had a suppressor cell defect (P less than 0.1). Among the 26 first-degree relatives with elevated 16/6 Id levels, 12 had associated suppressor defect and in only two cases was a suppressor cell defect unaccompanied by increased 16/6 (P less than 0.005). For the group of 18 patients and relatives showing concomitant suppressor cell defect and increased 16/6, a correlation was found between the severity of the suppressor cell defect and the level of 16/6 Id in the serum. The increased 16/6 in the relatives was not associated with hypergammaglobulinemia or with measurable anti-DNA activity in the serum. We conclude that the suppressor cell defect in relatives of SLE patients is often associated with increased expression of antibodies with the 16/6 idiotype. However, additional mechanisms are involved in the regulation of 16/6 Id and the development of clinical SLE, since increased 16/6 was commonly found in the presence of a normal suppressor T-cell function.