Rodgers (Rg) and Chido (Ch) determinants on human C4: characterization of two C4 B5 subtypes, one of which contains Rg and Ch determinants.

The genetically determined polymorphism of the fourth component of human complement was further extended with the aid of a panel of human allo-anti-C4 sera, anti-Rodgers and anti-Chido. These antisera were found previously to react with the alpha-chains of the C4 molecules controlled by the C4A and C4B loci, respectively. We analyzed a number of new and rare C4 allotypes, and found that they generally followed the expected pattern. Some interesting exceptions, however, were found. The alpha-chain of the allotype C4A1 was found to react with anti-Chido, unlike all other C4A allotypes. Also the C4B5 allotype could be subdivided into two subtypes on the basis of their reaction with anti-Rodgers. They were tentatively named B5Rg+ and B5Rg-. Moreover, the B5Rg+ subtype reacted not only with anti-Rodgers but also with some anti-Chido sera, indicating for the first time that Chido and Rodgers determinants are present on the same allotype.