HLA-B*4431: a new HLA-B variant with a complex ancestral history involving HLA-B*44, B*40 and B*07 alleles.

We here describe the identification of the new allele HLA-B*4431, which was found in three members of a Turkish family. Sequencing of the new allele following haplotype-specific PCR amplification revealed that exon 2 is identical to HLA-B*4402, whereas exon 3 resembles a HLA-B*40 variant with the exception of position 572, where a single nucleotide transversion (C > G) leads to an amino acid exchange (Trp162Ser). The generation of the 3' part of B*4431 may be best explained by a separate recombination between B*40 and B*07. Although B*4431 consists of B44 in its alpha1 domain and of B60(40) in its alpha2 domain; the new allele only displayed B44 seroreactivity, which demonstrates that epitopes crucial for B60(40) specificity must be located in the alpha1 domain.