ABSTRACT
In the HLA-DRB subregion of man, five major groups of haplotypes, often displaying a remarkable polymorphism, are distinguishable. The polymorphism is thought to be generated by point mutation, microgene conversion and gene rearrangement by recombination. In order to gain insight into the organization of the rhesus macaque major histocompatibility complex (MHC) class II region, DRB genes from monkeys of different origins previously typed for their DQ genes were analyzed. At first DRB haplotypes were deduced from DQ-homozygous monkeys. The stability of these haplotypes was then examined in DQ-heterozygous monkeys by sequence-based typing for the presence of members of the DRB1*03 and DRB1*04 lineage, and for seven single alleles detected on the haplotypes. Six DRB haplotypes linked to the five most frequent and three haplotypes linked to less frequent DQ haplotypes were identified. Six novel DRB alleles were detected. The number of DRB genes per haplotype varied between two and four. The results altogether suggest that in rhesus macaques, in comparison to man, the DQ haplotypes are linked to only a small number of DRB haplotypes, the number and diversity of DRB haplotypes is larger, and the allelic polymorphism of a given haplotype is smaller. The diversity of the DRB haplotypes was partly due to the varying number and identity of genes linked to DRB1*03 and DRB1*04. Furthermore, the number of DRB1 genes themselves varied from zero to two.