Mapping of the HLA locus controlling C2 structural variants and linkage disequilibrium between alleles C22 and Bw15

The newly discovered polymorphism of human C2 protein analyzed by isoelectric focusing is controlled by a locus closely linked to HLA. An informative cross-over family (HLA: A×C) indicates that this locus maps on the C side of the region. Population and family studies have shown that the C2² variant is significantly associated on the haplotype with alleles Bw15 and Cw3. The fact that the “deficient” C2 mutant is in linkage disequilibrium with other HLA antigens, suggests that C2² and C2⁰, here tentatively considered alleles of the same locus, are not directly related by descent.