Two HLA-linked loci controlling the fourth component of human complement.

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Abstract
An electrophoretic polymorphism of the 4th component of human complement (C4) is described. Three patterns of bands of C4 were observed in EDTA plasma from a panel of unrelated blood donors and family members using immunofixation electrophoresis. These patterns consisted of 4 fast-moving anodal bands (F), 4 slow-moving cathodal bands (S) or a combination of F and S bands (FS). The C4 patterns of bands were observed in EDTA plasma and not in serum. Family studies showed that this polymorphism of C4 did not segregate with HLA histocompatibility genes in a fashion governed by 2 codominant alleles at a single genetic locus. The family data are in agreement with the hypothesis that 2 different genetic loci control the electrophoretic patterns of C4. One locus controls the presence (F) or absence (fo) of the 4 anodal (F) bands and the other controls the presence (S) or absence (so) of the 4 cathodal (S) bands. The C4F and C4S loci are both closely linked to HLA-B.