A new HLA-DRB1 allele formed by an intraexonic interallelic crossover

Identification of three novel alleles of HLA-DRB1 and HLA-A in the Brazilian population

Two human leukocyte antigen (HLA)-DRB1 (HLA-DRB1*1376 and -DRB1*1465) and one HLA-A (HLA-A*2471) novel alleles have been identified in individuals from the Brazilian Bone Marrow Donor Registry. DNA sequencing of exon 2 for HLA-DRB1 alleles showed two and five nucleotide substitutions in -DRB1*1376 and -DRB1*1465, compared with closely related alleles, respectively. These substitutions result in a change of amino acid residues in HLA-DRB1*1376 at position 74 (Arg --> Glu) and in -DRB*1465 at positions 47 (Tyr --> Phe), 57 (Asp --> Ser) and 74 (Glu --> Ala). On the other hand, sequence analysis of exons 2 and 3 for HLA-A*2471 showed a single substitution, leading to a single amino acid change at position 151 (His --> Arg). These three novel alleles may have originated from other HLA alleles by gene conversion. However, it is also possible that HLA-A*2471 has evolved from one of the alleles of the HLA-A*2402 group through a point mutation.

Evolution of the ovine MHC DQA region

Southern hybridisation was used to define an apparent gene duplication event at the ovine DQA2 locus. Approximately 500 sheep from five different breeds were genotyped at their DQA1 and DQA2 loci. A subset of these were selected for further characterisation. Southern hybridisation of TaqI digested DNA revealed no DQA1 region in some sheep. It was also noted in these DQA1 null animals the DQA2 specific probe hybridised to two bands. An EcoRV-RFLP designed to distinguish copy number confirmed this duplication of the DQA2 region. The results showed that the duplication was exclusively associated with the DQA1 null haplotype and occurred only in alleles DQA2-F, -G, -I and -J. Comparison with bovine MHC genes revealed that they also contained a DQA1 null haplotype and that this haplotype was associated with a putative DQA3 gene. The potential for an ovine DQA3 locus is discussed.

Relative HLA-DRB1*13 allele frequencies and DRB3 associations of unrelated individuals from five US populations

The frequencies of 30 HLA-DRB1*13 alleles and 15 DRB3 alleles were determined for the 5 major U.S. ethnic populations: Caucasians, African Americans, Asian/Pacific Islanders, Hispanics, and Native Americans. A random sampling (163) of DRB1*13-positive individuals from each self-described ethnic group was selected out of a pool of 82,979 unrelated individuals, providing at least an 80% probability of detecting a rare allele that occurred at 1%. These 815 samples were subjected to allele-level SSOP typing and/or DNA sequencing which identified 11 different DRB1*13 alleles. DRB1*1301 and DRB1*1302 were the most common alleles seen in the five major ethnic groups while DRB1*1304 was not detected among Caucasians and DRB1*1305 was not detected among African Americans. DRB1*13 allele diversity was surprisingly more limited among African Americans compared to both Caucasians and Asian/Pacific Islanders. To determine the extent of DRB1*13-DRB3 associations, 504 of these samples expressing only one DRB3-associated DRB1 allele were subjected to PCR-SSOP typing and 14 DRB1*13-DRB3 haplotypes were detected. The distribution revealed that African Americans were significantly different from Caucasians, Asian/Pacific Islanders, and Hispanics. Allele frequency studies such as this further support previous findings that the distribution of HLA types can differ significantly among different ethnic populations.

Striking conservation of three extended HLA-DR13 haplotypes in the Japanese population

HLA class II DNA typing was conducted for 1335 unrelated Japanese individuals. The study on the linkage disequilibrium revealed a striking conservation of HLA DR13 haplotypes. Among these Japanese, 155 were typed for HLA-DR13 serologically, and they were correspondent to three DRB1 alleles, DRB1*1301, 1302 and 1307 defined by using the polymerase-chain reaction and sequence-specific oligonucleotide probe (PCR-SSOP) method. The two alleles, DRB1*1301 and 1307 were exclusively associated with each specific DRB3-DQA1-DQB1 combination which was DRB1*1301-DRB3*0101-DQA1*0103-DQB1*0603, and DRB1*1307-DRB3*0202-DQA1*0501-DQB1*0301, respectively. DRB1*1302, the most common DR13 allele in Japanese, had two significant associations with DRB3*0301-DQA1*0102-DQB1*0604 (DRB1*1302A) and with DRB3*0301-DQA1*0102-DQB1*0605 (DRB1*1302B). In this study, no other DR13 class II combinations were found. Only the DRB1*1302A halotype was associated with the DPB1*0401 allele while the DRB1*1302B haplotype was not. The complete conservation of these DR13 class II haplotypes was found to extend toward the HLA class I region. They were HLA A3-B44-DRB1*1301, A33-B44-DRB1*1302A and A33-B17-DRB1*1302B. Japanese could be characterized with these three extended haplotypes which were remarkably different from those in Caucasian, Black and Asian other than Korean populations.

Comprehensive typing of DR52 (DRB3)-associated DRB1 and DRB3 alleles by PCR-RFLP

The DR52-associated DRB1 and DRB3 alleles were resolved by PCR-RFLP. Second exon was amplified using four primer pairs (groups 1-4) for DRB1 and a pair for DRB3 alleles. Except for three endonucleases, all others had either none or only one site for a specific amplified product. Group 1 primers amplify 10 DRB1 alleles (DRB1*0302, 1101, 1302, 1303, 1305, 1307, 1402, 1403, 1407 and 1409). All but one pair, DRB1*1402 from 1409, could be resolved using seven endonucleases (ApaI, SacII, FokI, AvaII, BsaAI, BsrBI and SfaNI). Group 2 consisted of four alleles (DRB1*1201, 1202, 1404 and 1411) that can be resolved along with co-amplified DRB1*0804 and 0806 using five endonucleases (AvaII, SacII, FokI, HaeII and RsaI). Group 3 primers amplify 15 DRB1 alleles (DRB1*0301, 0303, 1102, 1103, 1104, 1107, 1301, 1304, 1306, 1308, 1401, 1405, 1406, 1408 and 14-New), which can be resolved using nine enzymes (KpnI, AvaII, FokI, SacII, HaeII, BsrBI, SfaNI, DdeI and RsaI). BsrBI, a new endonuclease, can resolve DRB1*1301 from 1306 and the previously unresolved allele DRB1*1103 from 1104. DRB1*1410, co-amplified with DR4 group-specific primers, is resolved with PstI which cleaves all DR4 alleles but not DRB1*1410. All four DRB3 alleles (DRB3*0101, 0201, 0202 and 0301) and their heterozygotes are resolved using two endonucleases, RsaI and HphI. Thirty-four DR52-associated alleles and their heterozygotes can be unambiguously resolved, except for DRB1*1402 from 1409.(ABSTRACT TRUNCATED AT 250 WORDS)