Lymphocytotoxic antibodies in family members of patients with systemic lupus erythematosus.

57% of sera from 124 relatives of 28 patients with systemic lupus erythematosus (SLE) were found to have antibody directed against lymphocytes. The incidence in 60 members of 16 control families was 3%. Both consanguineous and nonconsanguineous relatives had the antibody in their sera. 68% of close household contacts of the SLE patients showed lymphocytotoxic antibody whereas only 23% of consanguineous relatives who had no household contact with the probands had this antibody. These data suggest that environmental factors may be important in the pathogenesis of SLE.