The association of antinuclear antibodies, antilymphocyte antibodies, and C4 activation among the relatives of children with systemic lupus erythematosus.

We studied 31 children with systemic lupus erythematosus (SLE) and 108 first-degree relatives of the children to determine if HLA type, familial relationship to patient, or gender influenced the familial aggregation of SLE and the serologic and serum complement abnormalities associated with SLE. There were no significant relationships between the presence of antinuclear antibodies (ANA), antilymphocyte antibodies (ALA), or circulating immune complexes. Furthermore, there was no correlation between the occurrence of ANA, ALA, or circulating immune complexes with HLA type or relationship to patient. Both ANA and ALA were associated with a reduction in the mean serum C4 level, without a corresponding reduction in mean serum C3 or CH50. The reduction in mean serum C4 level with ALA occurred without regard to the subject's relationship to the patient, but the reduction in mean serum C4 level with ANA was significant only among the sisters. Because of these data, it seems that the sisters of patients with SLE are more likely than other relatives to have activation of the complement system in association with serologic abnormalities. Those sisters with ANA and ALA had the greatest amount of complement activation and may be the relatives at greatest risk for the subsequent development of SLE.