Apparent HLA DR triplet due to the coexpression of a DRB5-encoded molecule on a DR1 haplotype

HLA-DR polymorphism influences T-cell precursor frequencies to Epstein-Barr virus (EBV) gp110: implications for the association of HLA-DR antigens with rheumatoid arthritis

To study whether HLA-DR haplotypes associated with susceptibility to develop rheumatoid arthritis (RA) may influence T-cell responses to the Epstein-Barr virus (EBV) gp110 (a protein of the late replicative cycle of EBV), we evaluated the frequency in peripheral blood of T cells capable to proliferate to EBV gp110 by direct limiting dilution analysis in 50 HLA-DR-typed healthy subjects. NVe found that HLA-DRB1*07, an allele associated with reduced risk to develop RA, is associated with the highest frequencies of T cells specific for gp110 in peripheral blood. In contrast, HLA-DRB1*0404, one of the susceptibility alleles is associated with the lowest frequencies of gp110 specific T cells. Finally, people expressing both HLA-DRB1*07 and HLA-DRB1*0404 display low precursor frequencies to EBV gp110.

Presence of retroelements reveal the evolutionary history of the human DR haplotypes

Comparison of intron sequences has been a successful tool for drawing major conclusions about the evolutionary relationship of DRB genes. This complex family of genes is discussed in this review as well as a proposed model for the evolution of HLA-DR haplotypes. The model is based both on phylogenetic analysis of intron sequences as well as presence of ERV9 LTR elements located at identical position in intron 5 of a number of DRB genes. According to this model, two main evolutionary branches of DR haplotypes exist. The DR53 haplotype represents one branch, and the second branch contains the DR51, DR52, DR1, and DR8 haplotypes. After the divergence of the DR53 haplotype, an ERV9 LTR element was inserted in a primordial gene. Consequently, all DRB1 genes as well as the DRB3 gene within haplotypes of the second branch, contain this LTR element. In addition, conserved regulatory sequence motifs are found present within these LTR elements that might regulate DRB gene expression. Novel haplotypes are generated by recombinations and the maintenance of the DR haplotype variation as well as the frequent genetic rearrangements observed might be evolutionary advantageous.

A novel HLA haplotype containing a DRB5 gene associated with the DRB1*0103 allele

A new hybrid haplotype, a DRB1*0103 allele associated with a DRB5*0101 allele, was found in a French Caucasoid family and has been described here. When these cells were typed by serology, contrarily to cells with the DR1 + 2s haplotype, they did not seem to be triplets. The reactivity of these cells with the DR2 allosera led to a false serological HLA-DR typing. RFLP analysis and DNA oligotyping after DR1-DRB1, DR2-DRB1 and DRB5 group-specific amplifications showed that there was no DR2-DRB1 product in these cells and demonstrated the segregation of a DR103 DR51 haplotype in the family.

Serologic and molecular studies of two kindreds expressing recombinant HLA DR1/DR2 haplotypes

We have recently identified two unrelated kindreds in which DR1 and DR2 co-segregate as a single haplotype spanning several generations. Serology, PCR-RFLP and sequence-specific oligonucleotide probes were used to characterize the presence and segregation of the DRB1 and DRB5 loci in these two kindreds. In both families, the recombination resulted in co-expression of a DRB1 locus that encoded a DR1 serologic phenotype and a DRB5 locus that encoded a "short" DR2 serologic phenotype. One of these kindreds co-expressed the DR1 and DR15 (DRB5*01). The other kindred co-expressed the DR1 and DR16 (DRB5*02). Our data indicate that the recombination event occurred in the region between the DRB1 locus and the DRB5 locus. This recombinant haplotype produces a DR2 phenotype which lacks the epitopes normally encoded by the DRB1 locus, resulting in a serologic "short" antigen. The clinical significance of such a recombinational event becomes evident when patients with such a genotype require allogeneic bone marrow transplantation.