Genetic control of C6 polymorphism and C6 deficiency in rabbits

The genetic control of the sixth component of complement (C6) in rabbits has been studied by quantitation of C6 functional and antigenic levels and identification of polymorphism by isoelectric focusing (IEF) in gels. Patterns of inheritance of C6 variants in families carrying a silent gene for C6 were examined, and it was found that 3 common plasma phenotypic variants, C6 A, C6 B, and C6 QO were under the genetic control of allelic genes, C6*A, C6*B, and C6*QO. In IEF patterns, C6 A could be identified by its isoelectric point that was slightly more acidic than that of C6 B. C6 QO was undetectable because it lacked functional and antigenic activity. The C6*A/C6*B genotype displayed a mixed IEF pattern with bands characteristic of both C6 A and C6 B. Functional and antigenic levels of C6 that were found in heterozygous C6*A/C6*QO and C6*B/C6*QO rabbits were approximately one-half of the C6 levels found in the corresponding homozygous animals. The phenotypic variation closely resembles that previously observed in humans and rhesus monkeys, as well as preliminary data in rabbits. The patterns of inheritance indicated that the two common C6 structural genes and the deficiency gene were allelic variants at the same genetic locus.