Analysis of intron sequences at the class II HLA-DRB1 locus: Implications for the age of allelic diversity

Analyses of the coding sequences of HLA class II alleles have revealed high similarity between species, indicating that much of the polymorphism predates the separation of human (Homo) and chimpanzee (Pan), 4-7.4 million years ago. Recent studies of the intron sequences of alleles provide support for a much more recent origin and rapid generation of HLA alleles. At the DRBl locus, intron analysis indicates that most of the allelic lineages have diverged from each other before the separation of Ho,no and Pan, consistent with the exon analysis. However, the intron sequences of alleles within lineages are almost identical, indicating that many of the alleles have been generated after the divergence of the Homo and Pan lineages.