An apparent homozygous example of the HLA-DR2 variant, DR2.4(LUM)

An unusual DRB1*1503 haplotype without a detectable DRB5 locus in a black African family

A DRB1*1503 allele not associated with DRB5 locus has been detected in an African family during routine HLA typing for bone marrow transplantation. PCR/SSOP analysis showed the DR2-associated alleles in all the family members but the DRB5 locus appeared to be absent in the patient and his brother. The samples were then analyzed for the presence of DRB6 pseudogenes and we found that the unusual haplotype was associated with DRB6*0101 allele. This finding strengthen the hypothesis of a recombination hot spot between DRB1 and DRB6 genes.

New HLA-DR haplotypes containing the DRB6 pseudogene

An unexpected probe reaction pattern was observed in two samples during HLA-DR typing by PCR-Sequence Specific Oligonucleotide Probes. In order to confirm the unusual typings, samples were analyzed by PCR-Sequence Specific Primers, cloning, and nucleotide sequencing of the second exon of the HLA-DRB-genes. The confirmed DR, DQ phenotype for one sample was DRB1*0701, DRB4*01, DRB5*0101, DRB6*0201, DQB*0602, DQB1*0202. The phenotype of other sample was DRB1*1602, DRB1*1302, DRB3*0301, DRB6*0101, DQB1*0501, DQB1*0502. The first sample has the novel combination of DRB1*0701 with DRB5*0101 and DRB6*0201. The second sample has either DRB6*0101 together with DRB1*1602 in absence of any DRB5 allele or DRB6*0101 together with DRB1*1302, DRB3*0301. We postulate that the most likely haplotype in sample #1 is DRB1*0701; DRB5*0101, DRB1*0602 which could have arisen from gene conversion. The most likely haplotype in sample #2, DRB1*1602, DRB6*0101, DQB1*0502 would have arisen from an homologous recombination event.

Molecular characterization of the HLA-DR2LUM haplotype

Molecular studies of HLA-DRB, -DRA and -DQB1 genes in the variant DR2 haplotype, DR2LUM, were performed using the homozygous lymphoblastoid cell line, CTS. The results of HLA Class II gene RFLP and PCR analyses suggest that DR2LUM was created by a homologous recombination event between HLA-DR1 and HLA-DR15 haplotypes. Evidence for the presence of a recombinational "hotspot" in haplotypes possessing a DRB6 pseudogene is presented. The results of this study have important implications for detection of HLA-DR2 alleles in DRB gene oligotyping strategies, and suggest that the CTS cell line will be a useful addition to cell panels for characterizing HLA antisera.

Restriction fragment length polymorphism of HLA-DQ and -DR allogenotypes in normal southern Chinese

We have examined the Taq I restriction fragment length polymorphism (RFLP) of the MHC class II regions of 96 normal Southern Chinese with respect to the HLA-DRB, -DQA, and -DQB genes. The data were compared with the DR and DQ serotyping. RFLP correlates well with the serological typing of the DR types of Chinese. Variants are seen in DR2 and DR12. The variant in DR12 with a 10 kb at the upper band (DR12b) is not found in Caucasoids and is more frequent in Chinese (19.4% of the alleles). With the help of DQA and DQB RFLP the assignment of genotyping of DRB types is facilitated. Some of the linkage disequilibrium patterns among DRB, DQA and DQB are different from Caucasoids. This is particularly obvious in the DR2 and DR5 haplotypes. In the 96 Southern Chinese, the 3 commonest haplotype frequencies are: DR12b, DQ alpha 1b, DQ beta 3b (18.3%); DR9, DQ alpha 3, DQ beta 3a (15.7%); DR4, DQ alpha 3, DQ beta 3a (14.2%). The various DR beta, DQ alpha. DQ beta genes can be accurately defined in Chinese by RFLP. Polymerase chain reactions using sequence-specific primers were performed to confirm the various HLA-DRB and -DQB alleles. The use of RFLP is important in the study of HLA matching and HLA-disease association in Southern Chinese.

Combinatorial diversity in DR2 haplotypes

Sequence analysis has identified multiple alleles at two loci that encode for the DR2 specificity. The loci, DRB1 and DRB5, are in linkage disequilibrium which can extend to alleles of the DQ loci. Serologic, cellular, and sequence-specific oligonucleotide probe (SSOP) typing techniques have been used to identify the DR2 haplotypes. In this report, we have characterized by SSOP typing and cDNA/DNA sequence analyses the combinatorial diversity of DR2 haplotypes. Cells were selected on the basis of unique serologic reactivity, unique associations of alleles of DR and DQ loci, and/or presence in populations which have not been extensively characterized for HLA diversity. An asymmetric polymerase chain reaction (PCR) amplification was applied to rapidly screen unique cells and to characterize DNA sequence in conjunction with more conventional cDNA sequence analysis. The sequence data confirm the lack of a DRB5 locus in the DR2"LUM" specificity, the unexpected association of DRB1*1602 and DRB5*010 alleles in a nonCaucasoid population, and the association of the allele DRB1*1503 with DRB5*0101 in black African, African American and native American individuals. The DRB1*1503 and DRB5*0101 alleles were identified in an unusual haplotype, DR2,DQ2. The combinatorial diversity of the DR2 haplotypes is extended by these studies in nonCaucasoid populations.