Immunoglobulin class of antilymphocyte antibodies in systemic lupus erythematosus patients and their families.

Antilymphocyte antibody (ALA) in systemic lupus erythematosus (SLE) was studied using an indirect immunofluorescent technique with air-dried, acetone-fixed lymphocytes. Ninety-four per cent of patients with SLE and 65 per cent of their relatives had ALA. The ALA response in SLE patients involved antibodies of all classes. However, the ALA in their relatives was primarily of the IgM class. Restriction of the class of ALA in asymptomatic relatives is analogous to that seen with anti-RNA antibodies and suggests that the switch to production of autoantibodies of the IgG class may be important in the pathogenesis of SLE.