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

TLDR: Family studies showed that this polymorphism of C4 did not segregate with HLA histocompatibility genes in a fashion governed by two codominant alleles at a single genetic locus, in agreement with the hypothesis that two different genetic loci control the electrophoretic patterns of C 4.

Abstract: An electrophoretic polymorphism of the fourth 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 by using the technique of immunofixation electrophoresis. These patterns consisted of four fast-moving anodal bands (F), four slow-moving cathodal bands (S), or a combination of both the 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 two codominant alleles at a single genetic locus. The family data are in agreement with the hypothesis that two different genetic loci control the electrophoretic patterns of C4. One locus controls the presence (F) or absence (f0) of the four anodal (F) bands and the other controls the presence (S) or absence (s0) of the four cathodal (S) bands. The C4F and C4S loci are both closely linked to HLA-B.