EVOLUTIONARY RELATIONSHIPS OF HLA-DR8 ALLELES AND DESCRIPTION OF A NEW SUBTYPE (DRB1-ASTERISK-0806) IN THE ALGERIAN POPULATION

A new HLA-DR8 allele (HLA-DRB1 *0806) found in the Algerian population is described here. This allele has an exon-2 nucleotide sequence identical to that of the HLA-DRB1*0801 allele, except for a GGT to GTG change in codon 86, yielding an amino acid substitution (glycine to valine). This change is also found in other HLA-DRB1 and HLA-DRB3 evolutionary-related allele pairs. HLA-DRB1*0806 is the most frequent HLA-DR8 allele found in this population (three of eight HLA-DR8-positive individuals) and is included within the HLA-DQA1*0102-DQB1*0602 haplotype (HLA-DQ6 serotype). This combination of HLA-DQ alleles is sporadically found associated with other HLA-DR8 alleles in other ethnic groups, i.e., HLA-DRB1*0804 in Bushmen and in North American blacks and HLA-DRB1*0803 in African blacks. Also, the HLA-DRB1*0806-DQ6 haplotype only bears one HLA-DRB gene copy, a common characteristic of the HLA-DR8 haplotype family. An exon-2 HLA-DR8 dendrogram has also been constructed with the available sequence data, indicating that this new allele does not seem to be placed at a distance significantly different from the origin to that of HLA-DRB1*0804 (proposed to be the eldest in the HLA-DR8 allele diversification pathway). A possible HLA-DR8 evolutive pathway is postulated according to the available exon-2 HLA-DR8 allele sequences.