C4 allotypes and HLA-DR antigens in the family of a patient with C4 deficiency.

Major histocompatibility complex (MHC) haplotypes, including HLA-A, -B, -C and -DR and complotypes (BF, C2, C4A and C4B) were determined in a large family with inherited C4 deficiency. The propositus, a 12-year-old girl with complete C4 deficiency and SLE, had the MHC haplotypes HLA-A2,Cw3,-B40,-DR6,BFS,C2C,C4AQO,C4ABQO inherited from her father and HLA-A30,-B8,-DR3,BFF1,C2C,C4AQO,C4BQO from her mother. These haplotypes were identified in several of the healthy relatives, who were thus shown to be carriers of C4 deficiency. Most of the other haplotypes found in the family were not considered to be unusual in the general population. The complete absence of C4 in the patient was confirmed by studies of Chido and Rodgers antigens in the plasma and on the erythrocytes, the absence of plasma C4d fragments and by studies of C4 chain antigens by immunoblotting technique. The results of the genetic analysis, together with the findings in other cases of C4 deficiency, supports the possibility that complete C4 deficiency in itself predisposes to development of SLE without contribution of other MHC gene products.