Subtypes of B44 in six different populations.

We have investigated the distribution of HLA-B44 subtypes in various populations, see table. Of the five B44 subtypes investigated, two are apparently quite rare because they were only found in the local central european panel (B^*4404 and B^*4406). The european populations are characterized by a relatively high frequency of B^*4402, while in the Albanian, in the Asiatic and African populations, the subtype B^*4403 is prevailing. The distribution of the B44 subtypes in the Czech and the Munich population are virtually the same. We conclude from these data, that B44 subtypes have different distributions in different populations of the world and must therefore be taken into consideration when matching for bone marrow transplantation.     

HLA-B44 ALLELE FREQUENCIES AND HAPLOTYPIC ASSOCIATIONS IN THREE EUROPEAN POPULATIONS

HLA-B44 is among the most frequent class I antigens in many populations studied so far. It has been subdivided into seven allelic forms that can only be discriminated by DNA typing. Using a simple PCR/sequence-specific oligonucleotide hybridization procedure, we have analysed the frequency distribution of B44 subtypes in three European populations from Slovenia, the Netherlands, and Switzerland. B*4402 and B*4403 were by far the predominant alleles, B*4404 and 4405 were rare, while B*4406 and B*4407 were not observed. Interestingly, B*4402 and 4403 occurred with different frequencies in the three populations, with B*4402 being most frequent in the Swiss (65% vs. 57% in the Dutch, and 46.5% in the Slovenes). Of the 139 individuals studied, 60 HLA-B44 ABDR haplotypes could be determined by family studies. In the respective populations, the linkage disequilibria between B44 and other HLA antigens occurred with different frequencies. A2-B*4402 haplotypes were very frequent in the Swiss sample, mostly associated with DRB1*0101, 0401 and 1301. B*4402 was more often linked with non-A2 antigens in the Slovenes (predominantly A24, A28) than in the Swiss and the Dutch. The predominant association of B*4403 was with DR7: this haplotype was very frequent in the Swiss (82% of the B*4403 haplotypes), while lower frequencies were found in the Dutch (72%) and Slovenian (59%) populations. In the Swiss population, more than half of the B44-DR7 haplotypes were A23-B*4403-DR7 (53% of all B*4403 haplotypes). This haplotype was significantly less frequent in the Slovenian (6%) and in the Dutch (14%) populations. The second most frequent B*4403 haplotype in both the Swiss and Slovenes is the A29-B*4403-Cw*1601-DR7 haplotype (17.6 and 29.4%, respectively). Concomitant with the increased frequency of B*4403 in the Slovenes, a higher diversity of non-DR7 B44 haplotypes was observed in this population (41% of all B*4403 haplotypes). HLA-B44 oligotyping analysis allowed us to detect B44-subtype incompatibilities in several AB-sero, DRB1/B3/B5-oligo matched unrelated bone marrow donor/patient combinations. The different frequency distributions of HLA-B44 haplotypes in the three populations analysed in this study argue in favour of local volunteer bone marrow donor recruitment. This might significantly improve the chance of finding a highly matched donor for patients with less frequent A-B-DRB1 haplotypes.     

HLA-B44 subtyping in a Spanish population: further evidence of Caucasian population diversity

HLA-B44 is the most frequent HLA-B allele in Caucasian populations. Several B44 subtypes, B*4402-B*4406, have been identified in individuals with this ethnic origin. Mismatches among B44 subtypes have been described as major targets for allogeneic responses in bone marrow transplantation. We have developed a PCR-SSO method, based on a B12- specific DNA amplification of exon 2 through exon 3 and subsequent non radioactive hybridization with eight probes, which allow us to discriminate all B12 homozygous combinations. We applied this method to determine the frequency of B44 subtypes in a Spanish population, as well as their HLA-A.-C.-DRB1,-DRB3/DRB4/DRB5.-DQA1 and -DQB1 associated haplotypes. A total of 141 healthy unrelated Spanish individuals and 31 B44-bearing haplotypes were investigated. Four B44 alleles were identified, B*4402 (33%), B*4403 (66%), B*4404 (0.7%), and B*4405 (0.7%). Haplotype analysis showed a clear differentiated distribution pattern for the two major B44 subtypes. B*4402 is associated with Cw5 (11/13) and A2 antigens (10/13). In contrast, B*4403 is mainly found together with DRB1*0701 (14/16). An inverted B*4402/B*4403 frequency in comparison with other European and North American Caucasian populations, revealed the existence of an extended haplotype diversity between populations of the same ethnic origin. Apart from anthropological studies, high resolution typing for HLA class I antigens presenting molecular polymorphism will be of great relevance in unrelated bone marrow transplantation.     

Identification of HLA-B44 and HLA-B45 alleles using a nested arms-PCR method

The establishment of DNA based identification of HLA Class I specificities has made high resolution typing possible at the allelic level. With such methods, it is feasible to identify population variation in allelic frequencies. Working towards higher allelic resolution of the HLA Class I loci we have developed a panel of primers to identify all the known HLA-B^*44 alleles and B^*4501 using a nested ARMS-PCR approach. There are currently seven different B^*44 alleles identified: B^*4402, B^*44031, B^*44032, B^*4404, B^*4405, B^*4406 and B^*4407. The system was validated using DNAs from B lymphoblastoid cell lines which have been sequenced for their B^*44 alleles. Further typing has been performed on a panel of 29 cell lines from the IHW cell panel and some 37 samples collected as part of the anthropological study of the Orkney islanders, all of which were previously defined as being B^*44 by the 12th Workshop HLA Class I typing kit. In the Orcadian population B^*4402 was found in 28 individuals to be the most common B^*44 allele, with 18 of these individuals expressing the A^*02-Cw^*0501-B^*4402 haplotype. The remaining 9 B^*44 positive individuals were all found to express the A^*29-Cw^*1601-B^*44031 haplotype. Methods and results will be presented.     

Analysis of 250 HLA-B44 genotypes in European Caucasoids: high diversity and preferential ABCDRB1 associations in B*4402, B*4403, and B*4405 haplotypes

Based on high-resolution DNA typing within 235 pedigrees, a total of 250 HLA-A/B/C/DRB1/DRB3 genotypes have been characterized. These comprise 129 different B44 haplotypes, of which 73.6% occurred only once. Only four different B*44 alleles were identified: B*4402-4405, with B*4402 and B*4403 haplotypes accounting for 57.6 and 36.8%, respectively, of all haplotypes. Although the relative numbers of different A/B/C/DRB1/B3 haplotypic associations were similar in both B*4402 and B*4403 haplotypes, the genotypic profiles were quite different in the two groups. When associated with the A*0101, A*0201, A*2402, A*3201, and A*6801 alleles, a much more extensive polymorphism of B*4402 haplotypes with respect to HLA-C and DRB1 associations was disclosed. On the other hand, B*4403 haplotypes were more diverse in the A23-B44 and A29-B44 groups with respect to DRB1 associations. Considering B-C linkage, B*4402-Cw*0501, B*4402-Cw*0704, B*4402-Cw*1604, B*4403-Cw*0401, B*4403-Cw*1601, B*4404-Cw*1601, and B*4405-Cw*0202 accounted for 98% of all genotypes. Eight A/B/C/DRB1 haplotypes occurred at a relative genotypic frequency of >0.015, with A*2902-B*4403-Cw*1601-DRB1*0701 (11.2%) and A*0201-B*4402-Cw*0501-DRB1*0401 (8.4%) as the two most frequent genotypes. Some A and DRB1 alleles were predominantly, if not exclusively, associated with specific B-C pairs: A*0301 with B*4402-Cw*0501 and B*4403-Cw*0401; A*2301 with B*4403-Cw*0401; A*2608 with B*4402-Cw*0501; A*2902 with B*4403-Cw*1601; DRB1*0101/0401/0403/0404/1101/1104/0801/1301/1302 with B*4402-Cw*0501; and DRB1*0701 with B*4403-Cw*1601. On the basis of this dataset and our experience with searches for phenotypically matched unrelated stem cell donors, several ABDR haplotypes were identified that would confer a higher probability of B44- and C-incompatibility. The analysis of 112 consecutive unrelated stem cell donor searches revealed that 24% of the 400 tested donors were B44-mismatched, and that no single B44 allele- matched donor could be identified for only 7% of the patients. HLA-C incompatibility rate was 22.2% for the patients with > or =1 B44 allele-matched donor(s). This dataset can therefore be used as a predictive tool for B44- and C-disparities in unrelated stem cell transplantation.     

Analysis of HLA-B*44 alleles encoded on extended HLA haplotypes by direct automated sequencing

Abstract: We developed a PCR-based approach to sequence exons 2 and 3 of HLA-B44 alleles from genomic DNA. We applied this method to determine the B44 alleles encoded on extended HLA-A, B, DRB1, DQB1 haplotypes and the degree of mismatching for B44 alleles among marrow transplant patients and their unrelated donors (URD). A total of 81 samples was studied and included 38 patients, 42 donors and the cell "FMB"; the 80 clinical samples were comprised of 8 unpaired patients, 12 unpaired donors, and 30 URD-recipient pairs. Three alleles encoding B44 were identified, B*4402 (N=51), 4403 (N=32) and a new allele designated B*44KB and named B*4405 (N=4). Of the 27 patients for whom family study was available, there were 13 different B*4402, 7 different B* 4403 and 2 new B*4405 haplotypes. HLA-A2, Cw*0501, B*4402, DRB1* 0401, DQB1*0301 (n=2); A2, Cw*0501, B*4402, DRB1*1501, DRB5* 0101, DQB1*0602 (n=2); and HLA-A29, Cw*1601, B*4403, DRB1* 0701, DQB1*0201 (n=5) comprised the most common patient haplotypes. Of 30 URD-recipient transplant pairs studied, 27 were HLA-A, B serologically matched and DRB1, DRB3, DRB5, DQB1 allele matched, and 3 pairs were DRB1-mismatched. All B44 allele mismatching (N=3) occurred among the 27 matched pairs. The novel B*4402-variant sequence, HLA-B*4405, was identified in 4 individuals, and in each case was associated with an HLA-B44, Cw*02022, DRB1*0101, DQB1*0501 haplotype. HLA-B*4405 and B*4402 are identical in exon 2; in exon 3 however, B*4405 encodes T instead of G at nucleotide position 75 which translates to a substitution of tyrosine for aspartic acid at codon 116. Finally, the published B*4402 sequence derived from cell "FMB" was found to contain an error; the corrected B*4402 sequence encodes G rather than C at position 146 of exon 3.     

HLA-B*44 allele frequencies and haplotypic associations in Koreans

We have investigated the frequencies of HLA-B*44 alleles and their haplotypic associations with HLA-A, -C, and -DRB1 loci in 450 healthy unrelated Koreans, including 213 parents from 107 families. All 79 samples (17.6%) typed as B44 by serology were analyzed for B*44 alleles using polymerase chain reaction (PCR) single-strand conformation polymorphism (SSCP) method. A total of three different B*44 alleles were detected: B*44031 (allele frequency 4.7%), B*44032 (3.1%), and B*4402 (1.3%). Three characteristic haplotypes revealing strong linkage disequilibrium were A*3303-Cw*1403-B*44031-DRB1*1302 (3.6%), A*3303-Cw*07-B*44032-DRB1*0701 (2.8%), and A*3201-Cw*05-B*4402-DRB1*0405 (0.4%). In addition, a strong association was observed for B*4402 with A*0301. The B*4403-bearing haplotypes of Koreans appear to be relatively common in Asian populations, whereas the B*4402-bearing haplotypes share some similarity to those of Caucasians. HLA-B44 alleles demonstrate a limited allelic diversity and comprise distinctive extended haplotypes in the Korean population. It is suggested that the frequencies of B44 subtype mismatches among ABDRB1-matched unrelated donor-recipient pairs would be low in this population.     

HLA-Cw*0409N is associated with HLA-A*2301 and HLA-B*4403-carrying haplotypes

The associations of HLA-B*4402 and HLA-B*4403 with alleles of HLA-A and HLA-Cw were investigated in panels of HLA-B*4403 and HLA-B*4402 homozygous individuals and in selected individuals carrying HLA-Cw*04 and HLA-B*4403. Some of these individuals were genotyped and also carried (HLA-DRB1*0701, DQB1*02). Among the latter, we studied individuals carrying the conserved extended haplotype (CEH) [HLA-Cw*04, B*4403, FC31, DRB1*0701, DQB1*02]. Four different common (HLA-Cw*, B*44) haplotypes were identified that extended to the HLA-A locus: HLA-A*0201, Cw*0501, B*4402; HLA-A*2902, Cw*1601, B*4403; HLA-A*2301, Cw*0401, B*4403; and HLA-A*2301, Cw*0409N, B*4403. We identified eight unrelated examples of the allele HLA-Cw*0409N. HLA-A*2301 was associated with both HLA-Cw*0401 and HLA-Cw*0409N, suggesting that HLA-Cw*0409N may have arisen from a mutation in a CEH. We estimate that approximately 2 to 5 in 1000 Caucasian individuals carry the allele HLA-Cw*0409N, making it one of the most frequent null HLA alleles known to date. Our findings demonstrate the first example of three different HLA-Cw-determined subtypes of a common or CEH carrying a shared HLA-B allele, in this case HLA-B*4403.     

Differences in the recognition by CTL of peptides presented by the HLA-B*4402 and the HLA-B*4403 molecules which differ by a single amino acid

The HLA-B*4402 and B*4403 molecules differ only at residue 156, which borders the peptide binding site. Strong in vivo allogeneic reactions mediated by cytolytic T lymphocytes (CTLs) were reported in patients who received a bone marrow graft mismatched for these B44 subtypes, indicating that HLA-B*4402 and B*4403 molecules present distinct antigens. This could be due either to the presentation of different sets of antigenic peptides or to the recognition by CTLs of conformational epitopes formed by the MHC molecules alone or in association with antigenic peptides. To address this question, we compared the two B44 subtypes in their presentation to tumor-specific CTLs of three peptides, encoded by genes MAGE-3, MUM-1 and Tyrosinase. The peptides bound with similar affinities to B*4402 or B*4403 molecules, as assessed by lytic competition assays. One HLA-B*4402-restricted and one HLA-B*4403-restricted CTL clone were derived against each peptide. When tested for lysis of B*4402 and B*4403 cells incubated with the antigenic peptides, most CTLs showed a marked preference for one of the two B44 subtypes. Using variant peptides incorporating single alanine substitutions, we compared a given CTLs' recognition of its antigenic peptide presented by both B44 subtypes. Some substitutions, which had no effect on the binding of the peptide, affected its recognition by the same CTL differently on B*4402 and B*4403 molecules. These results imply that the conformations adopted by the same peptide on the two HLA-B44 subtypes are different. We conclude that the B44 subtype specificity of T cells results mostly from distinct conformations adopted by the same peptides in the two B44 molecules. This does not exclude the possibility that in some cases the B44 subtype specificity results from the selective binding of a peptide to one subtype. We found several peptides, different from the three mentioned above, that contain the canonical HLA-B44 binding motif and bind to B*4403 but not to B*4402 molecules.     

HLA-B40, B18, B27, and B37 allele discrimination using group-specific amplification and SSCP method

We developed a system for discriminating HLA-B40, B18, B27, and B37 alleles using a two-step PCR method followed by SSCP analysis. Fragments (0.8 kb) including exon 2, intron 2, and exon 3 were amplified in the first PCR. We used two sets of primers, one specific for HLA-B60-related alleles and the other specific for HLA-B6l-related, B18, B27, and B37 alleles. No amplifications of other class I genes or pseudogenes were observed. In the second PCR, exon 2 and exon 3 were amplified separately, using diluents of the first PCR products as templates. HLA-B6l-related, B18, B27, B37, and B60-related alleles were clearly discriminated in the SSCP analysis of the second PCR products. In a population study in which B6l alleles were analyzed, B^*4003 was detected in two Japanese individuals in addition to two B6l alleles previously reported to occur in Japanese, B^*4002 and B^*4006. The relative frequencies of B^*4002, B^*4006, and B^*4003 in Japanese were 58, 35, and 6%, respectively. The individuals having B^*4003 are the first non-South Americans in whom this allele has been detected. The SSCP banding patterns of 18 HLA-B60-positive Japanese population samples were identical to those of a B^*40012 sample for both exon 2 and exon 3. We also demonstrated that the B37 allele occurring in some Japanese is B^*3701.     

MOLECULAR TYPING AND HAPLOTYPIC ASSOCIATIONS OF HLA-B*44 SUBTYPES

The heterogeneity of HLA-B44 is confirmed and the sequence difference between the two major subtypes, B*4402,*4403, is attributed to one polymorphic site in the third exon. A method is described to discriminate B*4402 and B*4403, and the occurrence and linkage disequilibrium of B*44 subtypes is discussed. No example of B*4401 polymorphism in exon 2 was observed.     

HLA-B27 subtypes in chinese patients with ankylosing spondylitis

The HLA-B27 allele has been extensively studied due to its strong association with ankylosing spondylitis (AS). In order to identify B27 alleles in Chinese patients with AS from the Shanghai area, we joined the AHS#5 of the 12 IHW and total of 68 B27 positive patients and 7 B27 positive normal persons have been investigated using polymerase chain reaction and Dig-ddTUP labeled oligonucleotides. Three primer pairs, E403 and E90as, E91As and E136as, E91Bs and E18as, were used to amplify codons 40-90 of HLA-B related alleles, codon 91 to 136 of HLA-B^*2701-B^*2706 and B^*2708 and codons 91-180 of B^*2707. A total of 11 probes were used to distinguish 8 B^*27 alleles from B^*2701 to B^*2708. 68 AS patients contain 69 B27 alleles because one patient is heterozygous B^*2704/B^*2705. A total of 4 alleles of B^*27 were detected in the AS-patient group. B^*2704 is the most common B^*27 allele in both AS patients and controls with similar frequency, 76.8% and 71.4%, respectively. We found a high proportion of B^*2705 in both AS patient (20.3%) and control (28.6%) groups. Although the control group is quite small we are still able to deduce that B^*2704 and probably also B^*2705 seem to be associated with AS in Shanghai area patients We also found one AS allele typed as B^*2707. Interestingly, for the first time we detected B^*2706 in an AS patient, which would argue against a protective effect of B^*2706 on AS susceptibility in Shanghai Chinese. The conclusion from this study is that the distribution of B^*27 alleles is not significantly different between AS patients and controls. Expanded numbers of AS patients and especially of healthy controls in different ethnic groups will be necessary to assess the contribution of different B27 subtypes to AS susceptibility.     

Two new class I alleles (HLA-Cw15052 and B0706) constitute a novel haplotype in Caucasians.

HLA-Cw^*15 alleles have been previously described in association with the HLA-B specificities B51, B61 and B73. In this study, we have characterized a novel haplotype constituted by the new alleles Cw^*15052 and B^*0706.

The two variants of Cw^*1505 differ in a synonymous change in nucleotide 24 of exon 1 coding for the signal peptide. The new B^*0706 allele differs from B^*0702 and B^*0705 in single changes at exons 3 and 5, respectively, and could be considered an intermediate evolutionary step between them.

Even though strong linkage disequilibrium between the HLA antigens Cw7 and B7 has been observed, ‘HLA-C blank’-B7 haplotypes are not rare either. Cw^*15 and B7 have been found to be associated in several Caucasian individuals. Therefore, it is likely that Cw^*15 accounts for a part of the aforementioned ‘HLA-C blank’-B7 haplotypes.

With the identification of Cw^*15052, a previously proposed pathway for the evolution of Cw^*15 alleles can be completed and will be discussed.     

HLA-B44 subtyping in the Catalan population using reference strand mediated conformation analysis. Implications for the selection of unrelated bone marrow donors

Cytotoxic T lymphocytes (CTLs) reactive against the disparity between HLA-B*4402 and HLA-B*4403 have been reported after unrelated donor bone marrow transplantation. These CTLs have been associated with acute graft-versus-host disease and graft rejection. This study describes the HLA-B44-subtyping in the Catalan population using reference-strand mediated conformation analysis. It has been performed on 297 unrelated HLA-B44+ cord blood units from the Barcelona Cord Blood Bank (Barcelona, Spain). We have found a predominance of HLA-B*4403 (66.04%) over HLA-B*4402 (33.02%), whereas the predominant HLA-B44 allele in Northern Europe and the United States is HLA-B*4402. This inverted proportion between HLA-B44 subtypes in Mediterranean populations compared with other Caucasian populations suggests that HLA-B44 subtyping should be performed when an HLA-B44+ unrelated donor marrow is identified.     

Characterization of a new HLA-B allele (B3702) generated by an intronic recombination event

Routine serological HLA typing of a Syrian family revealed a Bw4-associated HLA-B blank antigen showing Mendelian segregation together with the haplotype A1, Cw2, DR11, DQ7. A more extensive serological analysis showed no conclusive typing reactions with sera towards HLA-B27 and HLA-B37 antigens. Full length cDNA was sequenced in both senses for two individuals. Comparison of the consensus sequence with all other HLA-B published sequences evidenced a new HLA-B allele, confirming, as serologically predicted, the greatest relationship to HLA-B37 and HLA-B27 genes. Based on the exon 2 sequence identity to B^*3701, this new allele has been designated B^*3702. Proteins derived from B^*3702 and B^*3701 differ in 9 amino acids at alpha 2 (7 residues), and in transmembrane and cytoplasmic domains. Exons 3 to 8 are identical between B^*3702 and a number of HLA-B27 subtypes (all except Oriental HLA-B27 subtypes B^*2704, B^*2706 and B^*2707). B^*3702 alpha 1 domain differs from those of B^*2701, B^*2702, B^*2703, B^*2705, and B^*2708 in 9, 11, 9, 7, and 11 residues, respectively. The mosaicism found in B^*3702 strongly suggests that this new allele could be derived by homologous recombination at the intron 2 region between the B^*3701 gene and some of the 5 non-oriental B27 subtypes.     

HLA-B35 alleles in 440 individuals from 16 different populations as assessed by DNA typing.

As part of the Anthropology Component, the distribution of HLA-B35 alleles (B^*3501 to 3513) was studied in 16 different populations by group specific amplification and SSOP hybridization. The results were as follows:

The predominant alleles in most Caucasian populations were 3501 > 3503 > 3502 > 3508. However, B^*3502 predominated in Jews, B^*3508 in Arabs, B^*3503 in Gypsies and Sardinians seem to have only B^*3501 and 3502. B^*3504, 3505, 3506 and 3509 were restricted to Amerindians, where there are still other new B35 variants to be characterized. In most individuals the different B35 alleles were found in phenotypic combinations with HLA-Cw4, suggesting that the B35, Cw4 haplotype may have existed before subtype diversification. A detailed analysis of HLA-B35 alleles in other populations might help to draw a precise picture of B35 evolution.     

Characterization of natural peptide ligands for HLA-B*4402 and -B*4403: implications for peptide involvement in allorecognition of a single amino acid change in the HLA-B44 heavy chain

Abstract: This study describes the characterization of endogenous peptides associated with the two major subtypes of HLA-B44. The two subtypes differ for a single amino acid substitution from Asp (HLA-B*4402) to Leu (HLA-B*4403) in position 156 of the α2 domain, causing strong alloreactivity in vivo. In order to study the involvement of peptides in this phenomenon, the peptide motifs of the two subtypes were determined from natural peptide pools using Edman degradation. The motif was found to be essentially identical for HLA-B*4402 and -B*4403, with a strong predominance for Glu at position 2, Tyr or Phe at positions 9 and 10 and hydrophobic residues, especially Met, at position 3. Two individual naturally processed ligands of HLA-B*4403 were sequenced and shown to be derived from intracellularly expressed proteins found in protein sequence databases. The sequence of these natural peptide ligands conform well to the determined motif. These data will allow the prediction of HLA-B44 restricted peptide epitopes from viral and tumor antigens of known amino acid sequences. Moreover, they indicate that the peptide repertoire presented by HLA-B*4402 and -B*4403 is very similar, suggesting that the strong alloresponse between these two subtypes is not due to presentation of a different set of self peptides.     

Analysis of endogenous peptides eluted from HLA-B27 variants: implications in the susceptibility to spondylarthropathies

Population studies suggest that some HLA-B27 subtypes (HLA-B^*2705, B^*2702) could be more strongly associated with the development of spondylarthropathies than others (B^*2703, B^*2706, B^*2709). Differences in the peptide binding groove could impose differences in the nature of peptides bound by these different alleles. We have eluted endogenous peptides from C1R-B^*2705 and B^*2703 transfectants. The B^*2705 HPLC profile was more complex than the B^*2703 one. Several B^*2705 and B^*2703 individual peaks were sequenced by Edman degradation and mass spectrometry. Some peptides were shared by both subtypes. One B^*2705 eluted peptide present in a major HPLC fraction was not found in the B^*2703 peptides. The corresponding synthetic peptide bound in vitro specifically to T2-B^*2705 and not to T2-B^*2703. This result emphasizes that even one amino-acid difference outside the major anchor binding pockets at position 59 between B^*2705 and B^*2703 could notably influence the endogenous peptides naturally presented. This could have consequences in terms of T cell repertoire selection and development of autoimmunity.     

Differential tapasin dependence of MHC class I molecules correlates with conformational changes upon peptide dissociation: a molecular dynamics simulation study

Efficiency of peptide loading to MHC class I molecules in the endoplasmic reticulum is allele specific and can involve interaction with tapasin and other proteins. Allele HLA-B*4402 depends on tapasin whereas HLA-B*4405 (Tyr116 instead of Asp in B*4402) can efficiently load peptides without tapasin. Both alleles adopt very similar structures in the presence of the same peptide. Molecular dynamics simulations on peptide termini dissociation from the alpha(1)/alpha(2) binding domains were used to characterize structural and free energy changes. The magnitude of the calculated free energy change and the shape of the free energy curve vs. distance for induced peptide C terminus dissociation differed for B*4405 compared to B*4402. Structural changes during C terminus dissociation occurred mainly in the first segment of the alpha(2)-helix that flanks the peptide C terminus binding region (F pocket) and contacts residue 116. This segment is also close to the proposed tapasin contact region. For B*4402, a stable shift towards an altered open F pocket structure deviating significantly from the bound form was observed. In contrast, B*4405 showed only a transient opening of the F pocket followed by relaxation towards a structure close to the bound (receptive) form upon C terminus dissociation. The greater tendency for a peptide-receptive conformation in the absence of peptide combined with more long-range interactions with the peptide C terminus facilitates peptide binding to B*4405 and correlates with the tapasin-independence of this allele. A possible role of tapasin in case of HLA-B*4402 and other tapasin-dependent alleles could be the stabilization of a peptide-receptive class I conformation.     

Human leukocyte antigen-A, -B, and -Cw polymorphism in a Berber population from North Morocco using sequence-based typing

Class I human leukocyte antigen (HLA) polymorphism was examined in a Berber population from North Morocco, named Metalsa (ME). All data were obtained at high-resolution level, using sequence-based typing. The most frequent alleles were: HLA-A*0201 and A*0101; HLA-B*44 (B*4403 and B*4402); B*0801 and the B*50 allele group (B*5001 and B*5002); HLA-Cw*0602; and Cw*07 group (Cw*070101, Cw*070102, Cw*0702, Cw*0704, and Cw*0706), and Cw*040101. The novel HLA-B*570302 allele was identified. It differs at position 486 and position 855 from B*570301, resulting in synonymous Thr and Val. The analysis also evidenced some alleles common in Africans (A*3402, A*6802, A*7401, B*1503, B*4102, B*4202, B*7801, B*5802, Cw*1701, and Cw*1703) and some uncommon alleles (A*3004, B*2702, B*2703, B*5001,02, B*3503, and Cw*0706). The predominant HLA-A-Cw-B-DRB1-extended haplotypes in ME population were A*0101-Cw*0501-B*4402-DRB1*0402, A*240201-Cw*0701-B*0801-DRB1*030101, A*2301-Cw*040101-B*4403-DRB1*040501, A*0201-Cw*040101-B*4403-DRB1*1302, and A*3002-Cw*0602-B*5002-DRB1*0406. This study demonstrates a strong relatedness of ME to other Moroccan and North African populations, some characteristics of sub-Saharan Africans and evidenced the influence of various immigrations during centuries. Nevertheless, this study highlights some unique genetic traits of the ME population compared to other ethnic groups within Morocco, which could be of great interest for clinical aims, transplantation, and diseases.