DNA sequence analysis of the C4 antigen WH: evidence for two mechanisms of expression

Amino acid and protein analyses have allowed the construction of a model for the C4-based Rodgers and Chido blood group antigens. The single low-frequency allele (WH) in this blood group system, however, has not been characterized at the molecular level. Two WH+ donors were studied by C4 agarose gel electrophoreses, immunoblot studies using monoclonal anti-Rg: 1 or anti-Ch: 1, serological phenotyping, polymerase chain reaction-restriction fragment length polymorphism of their C4 genes, and DNA sequencing of the WH allele. The first donor had the C4A1, A3 phenotype; the C4A1 carried Ch: 1, 3, 6 (thus exhibiting reversed antigenicity) and the C4A3 carried the WH antigen. The amino acid sequence of the WH allele was PCPVLD at positions 1101 - 1106, S at position 1157, and VDLL at positions 1188 - 1191. A second donor typed as C4A2, A4, B1 and was also WH+. Immunoblot analysis showed that a C4B1 protein expressed Rg: 1. Sequence analysis of the C4B genes showed the amino acids LSPVIH at positions 1101 - 1106, S at position 1157, and ADLR at positions 1188 - 1191. Thus, the WH antigen is a conformational epitope that can arise through different mechanisms on either a C4A or C4B gene.