Subtypes of HLA-B27: history and implications in the pathogenesis of ankylosing spondylitis.

HLA-B27 represents a family of 38 closely related cell surface proteins (encoded by the alleles HLA-B*2701-39) called subtypes of HLA-B27, most of which have evolved from the ubiquitous HLA-B*2705 (specifically the B*27052 allele). HLA-B27 subtypes are largely characterized by nucleotide substitutions (mostly nonsynonymous) in exons 2 and 3 which encode alpha1 and alpha2 domains ofthe peptide binding groove respectively. Table 1 shows the description of sequences of HLA-B27 allele sequences. The subtypes could have arisen from B*2705 by point mutation (B*2703, B*2709, B*2704), gene conversion (B*2701, B*2702, B*2708) and reciprocal recombination (B*2707) B*2706 could have arisen by interlocus gene conversion. Studies from different parts of the world reveal differences in the population distribution.