HLA class I region sequences, 1998

High-throughput genotyping of HLA-G, HLA-F, MICA, and MICB and analysis of frequency distributions in healthy blood donors from Catalonia

Similarly to HLA class I molecules, certain non-classical HLA class I genes and MHC class I polypeptide-related sequences A and B (MICA and MICB) act as ligands for KIR and NKG2D natural killer receptors. Although these genes are less polymorphic than HLA class I, few studies have analyzed their association with diseases. Information on allele frequencies in healthy donors is needed to map their distribution worldwide. This study is the first to analyze high-resolution HLA-G, HLA-F, MICA, and MICB allele frequencies using a novel high-throughput next generation-sequencing method. We analyzed DNA samples from 96 unrelated blood donors resident in Catalonia, Spain, and registered in the Barcelona Blood and Tissue Bank. Using the first two fields of the HLA nomenclature, we detected six HLA-G and two HLA-F alleles. The most frequent alleles were HLA-G*01:01 (77.08%) and HLA-F*01:01(84.90%). When the four fields were analyzed, we detected 16 and 10 alleles, respectively. Nineteen alleles were detected for MICA and 10 for MICB. The most frequent alleles in these cases were MICA*008:01 (16.15%) and MICB*005:02 (46.84%). All frequencies were in Hardy Weinberg equilibrium except MICA. We also estimated maximum-likelihood haplotype frequencies and calculated corresponding linkage disequilibrium (LD) values and found that few allele pairs were in disequilibrium. Strong LD between MICA and HLA-B (using data from a previous study) was observed. Our findings will be useful for guiding further research evaluating the functional role of these genes in different diseases and populations.

Endothelial cell activation and proliferation modulate NKG2D activity by regulating MICA expression and shedding

MICA are major histocompatibility complex class I-related molecules, expressed by endothelial cells (ECs), that may be targets for alloantibodies and NKG2D-expressing natural killer (NK) and T effector cells in organ allografts. This study shows that basal levels of MICA expressed on vascular ECs is sufficient to functionally modulate the expression and activity of the immunoreceptor NKG2D in allogeneic NK cells. We found that MICA expression is differentially regulated at the EC surface in response to cytokines. TNFα upregulates MICA while IFNγ significantly decreases MICA at the EC surface. Both cytokines induce the release of soluble MICA by ECs. Modulation of NKG2D correlates with the MICA level on the EC surface. Glycosylation and metalloproteinase activities account for major post-transcriptional mechanisms controlling MICA level and the function in ECs. Our results indicate that, in addition to the NFκB pathway, the mitogen-activated protein kinase pathways JNK, ERK1/2 and p38 are key signaling pathways in the control of MICA by the cytokines. Finally, we show that EC proliferation mediated by FGF-2 or wound healing increases the MICA level. Together, our data suggest that inflammation and proliferation regulate endothelial MICA expression and shedding, enabling ECs to modulate NKG2D activity on effector NK and T cells, and provide further evidence of a role for ECs in immunoregulation.

Risk Factors for Alloimmunisation after red blood Cell Transfusions (R-FACT): a case cohort study

INTRODUCTION

Individuals exposed to red blood cell alloantigens through transfusion, pregnancy or transplantation may produce antibodies against the alloantigens. Alloantibodies can pose serious clinical problems such as delayed haemolytic reactions and logistic problems, for example, to obtain timely and properly matched transfusion blood for patients in which new alloantibodies are detected.

OBJECTIVE

The authors hypothesise that the particular clinical conditions (eg, used medication, concomitant infection, cellular immunity) during which transfusions are given may contribute to the risk of immunisation. The aim of this research was to examine the association between clinical, environmental and genetic characteristics of the recipient of erythrocyte transfusions and the risk against erythrocyte alloimmunisation during that transfusion episode. METHODS AND ANALYSIS STUDY DESIGN: Incident case-cohort study.

SETTING

Secondary care, nationwide study (within the Netherlands) including seven hospitals, from January 2005 to December 2011.

STUDY POPULATION

Consecutive red cell transfused patients at the study centres.

INCLUSION

The study cohort comprises of consecutive red blood cell transfused patients at the study centre. EXCLUSION: Patients with transfusions before the study period and/or pre-existing alloantibodies.Cases defined as first time alloantibody formers; Controls defined as transfused individuals matched (on number of transfusions) to cases and have not formed an alloantibody.

STATISTICAL ANALYSIS

Logistic regression models will be used to assess the association between the risk to develop antibodies and potential risk factors, adjusted for other risk factors.

ETHICS AND DISSEMINATION

Approval at each local ethics regulatory committee will be obtained. Data will be coded for privacy reasons. Patients will be sent a letter and an information brochure explaining the purpose of the study. A consent form in presence of the study coordinator will be signed before the blood taking commences. Investigators will submit progress summary of the study to study sponsor regularly. Investigators will notify the accredited ethics board of the end of the study within a period of 8 weeks.

The IMGT/HLA database

It is 12 years since the IMGT/HLA database was first released, providing the HLA community with a searchable repository of highly curated HLA sequences. The HLA complex is located within the 6p21.3 region of human chromosome 6 and contains more than 220 genes of diverse function. Many of the genes encode proteins of the immune system and are highly polymorphic. The naming of these HLA genes and alleles and their quality control is the responsibility of the WHO Nomenclature Committee for Factors of the HLA System. Through the work of the HLA Informatics Group and in collaboration with the European Bioinformatics Institute, we are able to provide public access to this data through the web site http://www.ebi.ac.uk/imgt/hla/. Regular updates to the web site ensure that new and confirmatory sequences are dispersed to the HLA community, and the wider research and clinical communities.

Mechanisms of genetically-based resistance to malaria

Malaria remains one of the most prevalent parasitoses worldwide. About 350 to 500 million febrile episodes are observed yearly in African children alone and more than 1 million people die because of malaria each year. Multiple factors have hampered the effective control of this disease, some of which include the complex biology of the Plasmodium parasites, their high polymorphism and their increasingly high resistance to antimalarial drugs, mainly in endemic regions. The ancient interaction between malarial parasites and humans has led to the fixation in the population of several inherited alterations conferring protection against malaria. Some of the mechanisms underlying protection against this disease are described in this review for hemoglobin-inherited disorders (thalassemia, sickle-cell trait, HbC and HbE), erythrocyte polymorphisms (ovalocytosis and Duffy blood group), enzymopathies (G6PD deficiency and PK deficiency) and immunogenetic variants (HLA alleles, complement receptor 1, NOS2, tumor necrosis factor-α promoter and chromosome 5q31-q33 polymorphisms).

The IMGT/HLA database

It is 10 years since the IMGT/HLA database was released, providing the HLA community with a searchable repository of highly curated HLA sequences. The HLA complex is located within the 6p21.3 region of human chromosome 6 and contains more than 220 genes of diverse function. Many of the genes encode proteins of the immune system and are highly polymorphic. The naming of these HLA genes and alleles, and their quality control is the responsibility of the WHO Nomenclature Committee for Factors of the HLA System. Through the work of the HLA Informatics Group and in collaboration with the European Bioinformatics Institute, we are able to provide public access to this data through the website http://www.ebi.ac.uk/imgt/hla/. The first release contained 964 sequences, the most recent release 3300 sequences, with around 450 new sequences been added each year. The tools provided on the website have been updated to allow more complex alignments, which include genomic sequence data, as well as the development of tools for probe and primer design and the inclusion of data from the HLA Dictionary. Regular updates to the website ensure that new and confirmatory sequences are dispersed to the HLA community, and the wider research and clinical communities.

Individual variation in 3-methylbutanal: a putative link between human leukocyte antigen and skin microflora

The human derma emits volatile compounds whose interaction with a receiver's olfactory sensory system may affect individual recognition and mating preferences. Studies suggest that both genes and environmental factors determine characteristic odor of an individual. We used solid-phase microextraction and gas chromatography-mass spectrometry to identify 3-methylbutanal in human axillary odor; we showed that the abundance of this volatile compound varies significantly among individuals and demonstrated that its formation in vitro may be influenced by interaction between human leukocyte antigen peptide and dermal microflora.

The IMGT/HLA database

The human leukocyte antigen (HLA) complex is located within the 6p21.3 region on the short arm of human chromosome 6 and contains more than 220 genes of diverse function. Many of the genes encode proteins of the immune system and include many highly polymorphic HLA genes. The naming of new HLA genes and allele sequences and their quality control is the responsibility of the WHO Nomenclature Committee for Factors of the HLA System. The IMGT/HLA Database acts as the repository for these sequences and is recognized as the primary source of up-to-date and accurate HLA sequences. The IMGT/HLA website provides a number of tools for accessing the database: these include allele reports, sequence alignments, and sequence similarity searches. The website is updated every 3 months with all the new and confirmatory sequences submitted to the WHO Nomenclature Committee. Submission of HLA sequences to the committee is possible through the tools provided by the IMGT/HLA Database.

Engineering and characterization of a stabilized alpha1/alpha2 module of the class I major histocompatibility complex product Ld

The major histocompatibility complex (MHC) is the most polymorphic locus known, with thousands of allelic variants. There is considerable interest in understanding the diversity of structures and peptide-binding features represented by this class of proteins. Although many MHC proteins have been crystallized, others have not been amenable to structural or biochemical studies due to problems with expression or stability. In the present study, yeast display was used to engineer stabilizing mutations into the class I MHC molecule, Ld. The approach was based on previous studies that showed surface levels of yeast-displayed fusion proteins are directly correlated with protein stability. To engineer a more stable Ld, we selected Ld mutants with increased surface expression from randomly mutated yeast display libraries using anti-Ld antibodies or high affinity, soluble T-cell receptors (TCRs). The most stable Ld mutant, Ld-m31, consisted of a single-chain MHC module containing only the alpha1 and alpha2 domains. The enhanced stability was in part due to a single mutation (Trp-97 --> Arg), shown previously to be present in the allele Lq. Mutant Ld-m31 could bind to Ld peptides, and the specific peptide.Ld-m31 complex (QL9.Ld-m31) was recognized by alloreactive TCR 2C. A soluble form of the Ld-m31 protein was expressed in Escherichia coli and refolded from inclusion bodies at high yields. Surface plasmon resonance showed that TCRs bound to peptide.Ld-m31 complexes with affinities similar to those of native full-length Ld. The TCR and QL9.Ld-m31 formed complexes that could be resolved by native gel electrophoresis, suggesting that stabilized alpha1/alpha2 class I platforms may enable various structural studies.

HLA class I and class II genotyping in patients with Behcet's disease: a regional study of eastern part of Turkey

Class I human leucocyte antigen (HLA)-B51 is well known to be associated with Behcet's disease in many ethnic groups. However, there has been no published paper with respect to its association with HLA class I and class II among the Turkish people who live in the eastern region of Turkey. Moreover, as it is known that B51 antigen is encoded by 21 alleles, B*5101-5121, HLA-B51 allele typing was performed, as well as HLA class I and class II genotyping of 75 patients with the disease and the 54 individuals in the matched control group. The result shows that the HLA-B51 frequency was significantly higher (58.66%) in the patient group, compared to that in the control group (18.51%) (OR = 6.245). In the subtyping of B51 alleles, 44 B51-positive patients possessed B*5101 (45.5%), B*5108 (25%), B*5105 (9.1%) and B*5104 (4.5%). There was no significant difference in the HLA-B51 allelic distribution between the patient group and the control group. However, homozygous carriers of HLA-B51 showed considerably high risk (OR = 2.647) in the patient group, compared to that in the control group. In the genotyping of class II HLA alleles, while HLA-DRB1*04 (45.3%) and HLA-DRB1*07 (24%) were the predominant alleles in the patient group, DRB1*11 (50%) appeared to be more common in the control group.

Diversity and locus specificity of chicken MHC B class I sequences

The major histocompatibility complex B (MHC B) region in a standard haplotype of Leghorn chickens contains two closely linked class I loci, B-FI and B-FIV. Few sequences of B-FI alleles are available, and therefore alleles of the two loci have not been compared with regard to sequence diversity or locus specificity. Here, we report eight new B-F alpha 1/alpha 2-coding sequences from broiler chicken MHC B haplotypes, and a unique recombinant between the two B-F loci. The new sequences were combined with existing B-F sequences from Leghorn and broiler haplotypes for analysis. On the basis of phylogenetic analysis and conserved sequence motifs, B-F sequences separated into two groups (Groups A and B), corresponding to B-FIV and B-FI locus, respectively. Every broiler haplotype had one B-F sequence in Group A and the second B-F sequence, if it existed, clustered in Group B. Group B (presumptive B-FI locus) sequences identified in broiler haplotypes resembled the human MHC class I HLA-C locus in their distinctive pattern of allelic polymorphism. Compared with B-FIV, B-FI alleles were less polymorphic and possessed a conserved locus-specific motif in the alpha1 helix, but nevertheless demonstrated evidence of diversifying selection. One B-FI alpha 1/alpha 2-coding nucleotide sequence was completely conserved in four different broiler haplotypes, but each allele differed in the exon encoding the alpha 3 domain.

Quantification of maternal microchimerism by HLA-specific real-time polymerase chain reaction: Studies of healthy women and women with scleroderma

OBJECTIVE

Microchimerism (Mc), originating from bidirectional fetal-maternal cell traffic during pregnancy, has recently been identified in healthy adults and in patients with scleroderma (systemic sclerosis [SSc]). This study was undertaken to investigate the frequency and quantitative levels of maternal Mc (MMc) in healthy women and women with SSc.

METHODS

HLA-specific primers and fluorogenic probes were used in real-time quantitative polymerase chain reaction assays to detect and quantify MMc by targeting noninherited, nonshared HLA sequences. DNA-based HLA typing was conducted in 67 proband-mother pairs and in all children if the proband was parous. Statistical analysis was limited to 50 proband-mother pairs (including 32 healthy women and 18 women with SSc) in whom MMc could be distinguished from potential fetal Mc.

RESULTS

MMc in peripheral blood mononuclear cells was more frequent among women with SSc (72%) than healthy women (22%) (odds ratio 9.3, P = 0.001). However, levels of MMc, expressed as the genome equivalent of maternal cells per million (gEq/mil), were not significantly different (0-68.6 gEq/mil in SSc patients, 0-54.5 in healthy women). In additional studies, positivity for MMc was demonstrated in a bone marrow aspirate from an SSc patient in whom peripheral blood had been found to be negative for MMc on 4 occasions, and tissue from a subsequent autopsy of this patient had MMc levels of 757 and 1,489 gEq/mil in the lung and heart, respectively.

CONCLUSION

MMc is not uncommon in the peripheral blood of healthy adults, is increased in frequency in patients with SSc, and may be present in bone marrow and disease-affected tissues although absent in the peripheral blood.

HLA A*02 allele frequencies and B haplotype associations in Western Indians

The population of Western India is described as Australoid or Proto-Australoid elements with admixture from Caucasian, Mongoloid, and Aryan races. We investigated the frequencies of human leukocyte antigen (HLA) A*02 alleles and their B* allele haplotype associations among 664 healthy unrelated Western Indians. Fifty-one of 204 serologically typed A2 individuals were analyzed for 56 molecular A*02 subtypes using high resolution polymerase chain reaction-reverse line strip-sequence-specific oligonucleotide hybridization (PCR-RLS-SSOP). A total of seven different A*02 alleles were identified, A*02011 (16%), A*0203 (16%), A*0205 (2%), A*0206 (2%), A*0211 (52.9%), A*0222 (4%), and A*0236 (8%). The most common HLA B allele associated with A*02 was B*40. Among the 42 subtypes HLA B*4006 (37.22%) was the most frequent subtype. HLA A*0211 was highly frequent in this population, A*0206 and A*0203 are common alleles observed among Asian populations, whereas A*0205 occurs in Caucasians and Africans and A*0222 has been observed among Hispanics. A*0236 has been observed among the western Indians exclusively. Most of the HLA A*02 subtypes observed were associated with B*4006 haplotype, although A*0236 was with B*0702 or B*1302 among the western Indians. The prevalence of A*0211 at high frequencies, A*0222, A*0236 novel alleles along with A*02 related haplotypes, demonstrate a substantial heterogeneity, which may be a consequence of founder effect, racial admixture, or selection pressure due to environmental factors.

Defining the allelic variants of HLA A19 in the western Indian population

The population of western India is described as Australoid or proto-Australoid (elements) with Indo-Aryan racial admixture. The present study was undertaken to investigate the genetic diversity of human leukocyte antigen (HLA A19) in Western Indians, and to determine the frequency distribution of its molecular subtypes at the population level. The study revealed a high occurrence of A*3303 (56%) in this population along with other common oriental alleles. A*33 has been commonly observed in Asian Indians (18.1%), Hanza-Burush (15.7%), Punjabis (13.9%), and Japanese (11.2%) populations. A*33 has been reported with low frequencies among the Australasians, East European (Czech), North African (Noba), and Eastern Europeans (Slovenian). Significantly we observed a low frequency of A*29 and A*74 when compared with other populations among the A19 repertoire. Prevalence of HLA A*3303 at very high frequencies among Western Indians may be a consequence of the founder effect, racial admixture, or selection pressure due to environmental factors among this population.

Six new HLA class I alleles detected by PCR-SSO genotyping

This paper describes six new alleles; A*0240, A*2614, B*3924, B*4425, Cw*0807 and Cw*12023, which were discovered during routine genotyping with sequence specific oligonucleotides (SSO's). Five of the new alleles have changes in residues which belong to the antigen binding site of the HLA protein. These new variants may have altered antigen binding properties and may cause differential immunological responses that could affect transplantation outcome1.

Sequencing-based typing of HLA-B*51 alleles and the significant association of HLA-B*5101 and -B*5108 with Behçet's disease in Greek patients

Behçet's disease (BD) is widely known to be strongly associated with human leukocyte antigen (HLA) B51 in many different ethnic groups.Recently, HLA-B51 allele typing of Greek BD patients was performed to study the distribution of B*5101-B*5107 alleles in this Greek population, the B51 antigen strongly associated with BD was found to be predominantly encoded by allele B*5101. As it is now known that the B51 antigen can be encoded by 21 alleles, B*5101-B*5121, we performed HLA-B*51 allele genotyping among 58 Greek patients with BD. After serological HLA typing, typing of HLA-B*51 alleles was performed using the polymerase chain reaction-sequencing-based typing (PCR-SBT) method. The frequency of the B51 antigen was found to be significantly higher in the patient group as compared with the control group (75.9% of patients vs 22.0% of controls. In the genotyping of B51 alleles, 34 out of 44 B51-positive patients possessed B*5101, 13 out of the 44 carried B*5108. In contrast, all of the 9 B51-positive normal controls carried B*5101. This study revealed a strong association between Greeks with BD, both B*5101, B*5108, provided important insights into the molecular mechanism underlying the association between HLA status, this disease.

Elongation of the cytoplasmic domain, due to a point deletion at exon 7, results in an HLA-C null allele, Cw*0409 N

The development of molecular techniques for HLA typing has allowed the identification of genes previously assigned as serologic blank alleles. Lack or poor cell surface expression has been found for molecules coded by HLA-A, -B, -DRB4, -DRB5, and -DPB1 genes. In this report we describe the first HLA-C gene encoding for a null cell surface molecule. HLA-Cw*0409 N shows a point deletion at position 1095 within exon 7. This mutation provokes a codon reading shift, generating a new translation stop codon 97 bp downstream to that described in alleles normally expressed. This new stop codon location implies the presence of 32 extra amino acid residues in the cytoplasmic domain. Transfection experiments suggest that elongation of the cytoplasmic domain in Cw*0409 N would be the cause of cell surface expression failure, although Cw*0409 N heavy chain is able to create stable complexes with beta2-microglobulin. HLA-C fragment length analysis in a small selected group of samples with B44-Cblk haplotypic associations allowed us to identify two additional subjects showing both a serologic silent Cw*04 allele and a point base deletion at the 3' end of the HLA-C gene. This finding indicates that the allele frequency of Cw*0409 N within serologic C blank alleles would be appreciable, although basically restricted to the (A23)-Cw*0409 N-B*4403-DR7-DQ2 haplotype.

The clinical importance of variation within the HLA-Bw4 complex

BACKGROUND

Antibody screening of a patient with a failed renal transplant showed positive reactions with most, but not all HLA-Bw4-associated B-locus antigens. However, the patient's serological HLA class I type suggested the presence of HLA-Bw4.

METHODS

Standard molecular techniques were used to re-type the patient and donor. ELISA antibody screening helped determine the patient's antibody specificity.

RESULTS

The patient's type was HLA-B*1402,4703;Bw6 and the donor HLA-B*4703,51011;Bw4,6. Analysis of ELISA results identified three amino acids (positions 77,80,81) as the most likely epitope recognised by the patient's serum. These corresponded to HLA-B*51011 amino acid mismatches, explaining the lymphocytotoxic reactivity pattern. This epitope is located on a subgroup of the HLA-Bw4 antigen suggesting anti-Bw4 was not a sufficient description of this antibody.

CONCLUSIONS

This report identifies an antibody to a sub-group of the Bw4 public specificity and also confirms the need for sequence-level analysis in the tissue-typing laboratory to determine future unacceptable mismatches.

HLA-B*51 allele analysis by the PCR-SBT method and a strong association of HLA-B*5101 with Japanese patients with Behçet's disease

Behçet's disease (BD) is known to be associated with human leukocyte antigen (HLA) B51 in many different ethnic groups. An increased incidence of HLA-B51 in the patient group has also been reported in a Japanese population. Recently, the B51 antigen has been identified to comprise 21 alleles, B*5101-B*5121. Further, not only HLA-B*5101 but also HLA-B*5108 were found to be relatively increased in the patient groups among Italian and Saudi Arabian populations. Therefore, we performed HLA-B*51 allele genotyping by the polymerase chain reaction-sequencing based typing (PCR-SBT) method in order to investigate whether there is any correlation of one particular B51-associated allele with Japanese BD. Ninety-six Japanese patients with BD and 132 healthy Japanese volunteers were enrolled in this study. As a result, the phenotype frequency of the B51 antigen was confirmed to be remarkably increased in the patient group as compared to the ethnically matched control group (59.4% in patients vs. 13.6% in controls; Pc=0.0000000000098, R.R.=9.3). In the B*51 allele genotyping, 56 out of 57 B51-positive patients were defined as B*5101 and the remaining one was B*5102. In contrast, all of 18 B51-positive normal controls were B*5101. None of the Japanese patients and healthy controls carried the HLA-B*5108 allele. This study revealed that B*51 allelic distribution in Japanese was different from those in Italian and Saudi Arabian populations, and that the significantly high incidence of the HLA-B51 antigen in the Japanese BD patient group was mostly caused by the significant increase of the HLA-B*5101 allele.

PCR-RFLP typing detects new HLA-DRB1 alleles: DRB1*13022, DRB1*1336 and DRB1*1435

It is difficult to resolve all heterozygous combinations of the HLA-DRB1*03, *08, *11, *12, *13 and *14 allele group in a one-step generic HLA-DRB1 typing system. Therefore, it is common to employ a secondary technique utilizing group-specific primers to amplify this group of alleles separately from the other HLA-DRB1, -DRB3, -DRB4 and -DRB5 alleles. This paper describes a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method for broad typing of the HLA-DRB1*03, *08, *11, *12, *13 and *14 alleles which, as well as being time-efficient and cost-effective, has so far allowed the detection of 10 new alleles. The new alleles were identified after following up unusual or novel PCR-RFLP patterns. Of the 10 novel alleles found so far with this method, seven have been described previously while three, DRB1*13022, DRB1*1336 and DRB1*1435, are presented here.

HLA-B27 and genetic predisposing factors in spondyloarthropathies

With the mapping of the human genome having been completed, our ability to investigate and ideally better understand the genetic basis of rheumatic diseases is advancing at a rapid pace. Substantial evidence strongly favors a direct role for HLA-B27 in genetic susceptibility to ankylosing spondylitis and related spondyloarthropathies, although the underlying molecular basis has yet to be identified. HLA-B27 contributes only 16 to 50% of the total genetic risk for the disease, clearly indicating that other genes must be involved. However, no other putative disease genes have yet been absolutely proven. Potential genes include MHC (HLA class II, low molecular weight proteasome [LMP], transporter associated with antigen processing (TAP), tumor necrosis factor [TNF]-alpha, and major histocompatibility complex class I chain-related gene A (MICA), as well as non-MHC genes (IL-1RA, IL-6, IL-10, and CYP2D6). Genome-wide screens have identified other chromosomal areas of interest: 1p, 2q, 6p, 9q, 10q, 16q, and 19q. However, different studies have given conflicting results. HLA-B27 itself is a serologic specificity, which encompasses 25 different alleles that encode 23 different products (proteins): HLA-B*2701 to B*2723. These alleles may have evolved from the most widespread subtype, B*2705, and two of them, B*2706 in Southeast Asia and B*2709 in Sardinia, seem not to be associated with ankylosing spondylitis. The distinction between the disease associated and nonassociated subtypes may provide clues to the actual role of B27 in disease pathogenesis.

HLA class I and class II are both associated with the genetic predisposition to primary Sjögren syndrome

Primary Sjögren syndrome (pSS) is an autoimmune disease characterized by progressive destruction of the exocrine glands leading to mucosal and conjunctival dryness. It is marked by lymphocytic infiltration of the glands and the accumulation of several types of autoantibodies such as rheumatoid factor (RF), antinuclear, anti-SS-A (anti-Ro) and anti-SS-B (anti-LA) autoantibodies. The susceptibility to pSS and/or the presence of SS-A/SS-B autoantibodies in pSS patients is associated with DRB1*03-DQB1*02 and DRB1*02-DQB1*06 haplotypes, whereas no associations have been described with any HLA class I allele. To define the impact of HLA class I alleles in predisposition to pSS, 46 patients responding to the European criteria and 222 healthy unrelated Caucasians were analyzed for their HLA class I and class II haplotypes. Our results confirm the association of the DRB1*03-DQB1*02 haplotype with SS-A/SS-B autoantibodies positive pSS and demonstrate a significant association of the HLA-A24 with the disease. Moreover, HLA-A24 is more often associated with DRB1*11-DQB1*0301 and/or DRB1*0301-DQB1*02 in pSS patients than in the controls. The novel association of HLA class I alleles with susceptibility to pSS provides new insights to the genetic predisposition to this disease and subsequently to its physiopathology.

MICA and MICB genes: can the enigma of their polymorphism be resolved?

The human MHC class I chain-related genes (MICA and MICB) are located within the HLA class I region of chromosome 6. Their organization, expression and products differ considerably from classical HLA class I genes. MIC proteins are considered to be markers of "stress" in the epithelia, and act as ligands for cells expressing a common activatory natural killer-cell receptor (NKG2D). Molecular models are now available for the MICA protein, both bound and complexed with NKG2D. MICA molecules appear to be highly flexible and polymorphic, although the functional relevance and implications of their polymorphism have yet to be fully discerned.

Sequencing based typing for HLA-C. Identification of three new alleles: Cw*0307, Cw*0502 and Cw*0504

HLA-C has been described as a transplantation locus in the unrelated bone marrow transplantation setting, and noticeably the number of mismatches between HLA-A,-B,-DRB1 compatible pairs is considerably high. Sequencing based typing (SBT) is an accurate and efficient methodology utilised in the HLA class I and II allele level of resolution. SBT for HLA-C locus was applied on a sample of 40 HLA-A,B,DRB1,DRB3/4/5,DQB1-compatible bone marrow recipient-donor pairs, and 3 new HLA-C alleles have been found. Cw*0307, well defined by serology as Cw3, showed two amino acid changes at the NK motif 77-80 regarding all described Cw*03 alleles, N77K80 instead of S77N80. Two new Cw*05 alleles were described, Cw*0502 properly typed by serology, and Cw*0504 that behaves as a short antigen. Cw*0502 differed from Cw*0501 by only one nucleotide at exon 3, that generated an amino acid replacement at codon 177, K to E. Cw*0504 differs from Cw*0501 by two clustered amino acid positions (114 and 116) placed at the peptide binding site. The rate of new HLA-C alleles found in this small series evidences a high grade of hidden HLA-C diversity in the Spanish population, particularly in the well-defined serologic specificities.

Molecular diversity of HLA-A*02 in Asian Indians: predominance of A*0211

The North Indians are considered predominantly Caucasoid with an admixture of genes from the Mongoloid and Aryan races. The present study was undertaken to investigate the genetic diversity of HLA-A*02 in the North Indian population and determine the frequency distribution of its molecular subtypes at the population level. The study revealed a high occurrence of A*0211 (33.8%) in this population along with increased frequencies of the common Oriental alleles, A*0206 (7.5%) and A*0207 (32.5%) and also of HLA-A*0205 (15%) commonly observed in negroid populations. HLA-A*0211 has only been reported with very low frequencies among the Ticuna Jews, Thai population, and Colombian Blacks in the malaria endemic areas of Africa. Significantly, we observed an unexpectedly low frequency of A*0201 (3.8%) in contrast to its distribution in Western Caucasians in whom it constitutes 95% of the HLA-A2 repertoire. Prevalence of HLA-A*0211 at very high frequencies among North Indians may be a consequence of the founder effect, racial admixture or selection pressure due to environmental factors in this population.

HLA class I genotyping including HLA-B*51 allele typing in the Iranian patients with Behçet's disease

It is well known that Behçet's disease (BD) is strongly associated with human leukocyte antigen (HLA) B51 in many ethnic groups. However, there has been no published report as yet with respect to this association among the Iranian people. Furthermore, since it is now known that the B51 antigen can be encoded by 21 alleles, B*5101-B*5121, we performed HLA-B*51 allele typing as well as HLA class I genotyping of 48 Iranian patients with this disease. As a result, the frequency of the B*51 allele was significantly higher (62.1%) in the patient group as compared with the ethnically matched control group (31.8%) (Pc=0.067, R.R.=3.51). In the genotyping of B*51 alleles, 33 out of the 36 B*51-positive patients possessed B*5101 and the remaining 3 carried B*5108. This study revealed that Iranian patients with BD also had a strong association with HLA-B51. In addition, this significantly high incidence of HLA-B*51 was found to be caused by an increase in both the HLA-B*5101 and HLA-B*5108 alleles. However, there was no significant difference in the HLA-B*51 allelic distribution between the patient and control groups.

Novel HLA allele, HLA-B*4013, identified from a potential bone marrow recipient. Putative gene conversion events with donor sequence

A new B40 allele was identified in a leukemic Caucasian patient. This allele, designated B*4013, differs in alpha 1 domain from B*4002 at six amino acidic positions: 67, 77, 80, 81, 82 and 83. Most of this substitutions could alter the antigen binding site of the HLA-B molecule. B*4013 may have originated by gene conversion or reciprocal recombination involving B*4002 as the recipient allele of sequence donated by B*4406. The new allele was serologically typed as a "blank" associated with the Bw4 epitope.

Ramifications of HLA class I polymorphism and population genetics for vaccine development

HLA polymorphism can complicate the design and development of vaccines, especially those that contain a selected number of epitopes and are directed at pathogens prevalent worldwide. Because of HLA class I restricted antigen recognition and ethnic variation in HLA distribution, such vaccines may not be uniformly effective across populations. We, therefore, considered whether it is possible to assemble a panel of HLA-A and/or HLA-B alleles that would allow the formulation of a single vaccine for a set of Caucasian, Black, or Asian populations. In applying an algorithm to predict levels of favorable response, we identified predominant alleles in 15 representative populations. Approximately 80% of the individuals in one African Black population and five Asian populations were positive for at least one of three HLA-A alleles. Eighty percent coverage was also theoretically possible in five Caucasian populations with only five HLA-A alleles. Four of five Black populations analyzed also required five alleles, but the allelic combinations differed. Our findings suggest that HLA-A alleles may be preferred targets because of the increased heterogeneity at HLA-B, although addition of a single HLA-B allele to a set of HLA-A alleles improved coverage. This approach provides for the identification of combinations of alleles that represent a desired percentage of a population and that could be targeted in designing vaccines. For vaccines with known HLA-restricted epitopes, it allows a prediction of theoretical levels of "responder" and "non-responder" status. Finally, these results might be used in the analysis of protein sequences to identify potential CD8+ T-cell epitopes in populations of interest. Biologic variables that may have further relevance are discussed.

IMGT/HLA Database--a sequence database for the human major histocompatibility complex

The IMGT/HLA Database (www.ebi.ac.uk/imgt/hla/) specialises in sequences of polymorphic genes of the HLA system, the human major histocompatibility complex (MHC). The HLA complex is located within the 6p21.3 region on the short arm of human chromosome 6 and contains more than 220 genes of diverse function. Many of the genes encode proteins of the immune system and these include the 21 highly polymorphic HLA genes, which influence the outcome of clinical transplantation and confer susceptibility to a wide range of non-infectious diseases. The database contains sequences for all HLA alleles officially recognised by the WHO Nomenclature Committee for Factors of the HLA System and provides users with online tools and facilities for their retrieval and analysis. These include allele reports, alignment tools and detailed descriptions of the source cells. The online IMGT/HLA submission tool allows both new and confirmatory sequences to be submitted directly to the WHO Nomenclature Committee. The latest version (release 1.7.0 July 2000) contains 1220 HLA alleles derived from over 2700 component sequences from the EMBL/GenBank/DDBJ databases. The HLA database provides a model which will be extended to provide specialist databases for polymorphic MHC genes of other species.

High resolution HLA class I and II typing and CTLp frequency in unrelated donor transplantation: a single-institution retrospective study of 69 BMTs

The results of unrelated donor transplantation (URD-BMT) are difficult to analyze since the continuous advances in HLA typing technology allow the detection of new mismatches unknown at the time of transplantation. We sought to confirm that matched recipient-donor pairs are in fact often mismatched when advanced HLA typing techniques are used. We retrospectively studied the impact of the results of high resolution HLA typing for HLA class I (-A, -B, -C) and HLA class II (-DR, -DQ, -DP) loci, and cytotoxic T lymphocyte precursor (CTLp) frequency, on the outcome of 69 URD-BMT procedures. At the time of transplant, six (6/69) and two (2/69) donor-recipient pairs were mismatched for HLA class I (-A and -B by serology) and HLA class II, respectively, while one pair was mismatched for both HLA class I and II. Using high resolution DNA typing, HLA class I mismatches were found in 31 (45%) pairs and HLA class II mismatches in nine (13%) pairs. Twenty-three of the 69 pairs were HLA-C mismatched. Low CTLp frequencies were found among the 19 HLA class I matched pairs tested, and also in 5/14 mismatched pairs (of whom three had severe aGVHD). The overall survival of the cohort was 28 +/- 6%. Among the 33 patients who were fully matched with their donors, the survival rate was 66% in the 18 patients with a standard hematological risk and 9% in the 15 high risk patients. Only two of the 33 patients developed severe aGVHD, and only one had graft rejection. Among the 36 mismatched pairs, the survival rate was 31% in the 13 patients with a standard hematological risk and 8% in the 23 high risk patients. Sixteen of these 36 patients died from severe aGVHD and four had graft failure or rejection. Three of the 10 patients with only an HLA-C mismatch died from severe aGVHD, and two had graft rejection.

IN CONCLUSION

(1) donor-recipient matching based on high resolution HLA class I and II DNA typing is associated with significantly better outcome after URD-BMT; (2) the results of URD-BMT with classical GVHD prevention are comparable to those of geno-identical BMT when donor and recipient are fully matched for HLA-A, -B, -C, -DRB1 and -DQB1 on the basis of high resolution typing; (3) CTLp frequencies do not correlate constantly with HLA class I matching, and our results fail to show that CTLp assay can distinguish between permissible and non-permissible class I mismatches; (4) clinical trials involving donor-recipient pairs with known HLA class I mismatches are needed to improve aGVHD prevention without increasing graft failure rate.

HLA-B*15 diversity in the Korean population

Alleles in the HLA-B*15 group encode molecules belonging to several serologic subgroups, B15 (B62, B63, B75, B76, B77) and B70 (B71, B72), representing many of the most problematic types to assign in routine clinical typing laboratories due to their serologic cross-reactivity resulting from structural similarity. More than 25% of Koreans express HLA-B molecules encoded by the HLA-B*15 alleles. To further characterize HLA-B*15 in this population, B*15-specific polymerase chain reaction (PCR) and sequence-specific oligonucleotide probe (SSOP) hybridization analysis using 39 digoxigenin-labeled probes were applied to DNA samples obtained from 237 B15/B70 serologically positive unrelated individuals. Nine B*15 alleles were identified. B*1501 was the most frequent allele (64.8%) followed by B*1511 (14.1%), B*1507 (8.6%), and B*1518 (5.5%) comprising more than 90% of B*15-positive samples. B62 molecules encoded by 4 of the identified alleles (B*1501, B*1507, B*1525, and B*1527) could not be discriminated by serologic reaction patterns. Among the fifteen B15/B70 apparent homozygotes, eight were heterozygotes carrying two different B*15 alleles. Several B*15 alleles exhibited strong associations with specific Cw, DRB1, and A allelic types (e.g., B*1507-Cw3 (22/22); B*1507-DRB1*04 (21/22), B*1507-A24 (17/22)). The data obtained in this study confirmed B*15 diversity in the study population and will be useful in hematopoietic stem cell donor searches as well as in determining the supplementary DNA typing strategy for B15/B70-positive samples in this population.

Molecular strategies to define HLA haplotype loss in microdissected tumor cells

Loss of heterozygosity (LOH) of chromosome 6p21 is an important mechanism that generates HLA haplotype loss in various human tumors. This mechanism produces non-reversible HLA-deficient tumor cells that can escape T cell immune responses in peptide-vaccinated cancer patients. However, the exact frequency of this mechanism is still unknown, because contaminating stroma in solid tumor tissues masks the tumor DNA obtained from solid samples. A microdissection technique was applied to 4-8 microm sections of cryopreserved tumor tissues from a group of colorectal and laryngeal carcinomas. Fifteen patients were analyzed for the presence of LOH associated with the beta(2)-microglobulin gene in chromosome 15, and five patients for LOH associated with HLA genes in chromosome 6. In two cases, autologous metastasis tissue samples were also available. The patients were selected for showing an altered HLA class I tumor phenotype as determined by immunohistological techniques. DNA was obtained from this microdissected material and amplified in order to detect the presence or absence of nine previously selected microsatellite markers. HLA sequence based typing (SBT) was also applied to these microdissected DNA samples to define the HLA genotype. Microdissection greatly improved the definition of LOH, with nearly 100% signal reduction in one of the alleles. In addition, this procedure allowed us to detect beta(2)-microglobulin LOH in tumors that expressed some HLA molecules. Our data indicate that this procedure can be successfully applied to microdissected samples from solid tumors, thus enhancing the power and sensitivity of LOH detection.

Analysis of the distribution of HLA-A alleles in populations from five continents

The variation and frequency of HLA-A genotypes were established by PCR-SSOP typing in diverse geographically distributed populations: Brazilian, Colombian Kogui, Cuban, Mexican, Omani, Singapore Chinese, and South African Zulu. HLA-A allelic families with only one allele were identified for HLA-A*01, -A*23, -A*25, -A*31, -A*32, -A*36, -A*43, -A*69, -A*80; and with two alleles for HLA-A*03, -A*11, -A*26, -A*29, -A*33, -A*34, and -A*66. Greater variation was detected for HLA-A*02, -A*24, and -A*68 allele families. Colombian Kogui and Mexican Seris showed the least diversity with respect to HLA-A alleles, albeit with small numbers tested, with only four and five HLA-A alleles identified, respectively. It would appear by their presence in all populations studied, either rural or indigenous, that certain alleles are very important in pathogen peptide presentation.

Going back to the roots: effective utilisation of HLA typing information for bone marrow registries requires full knowledge of the DNA sequences of the oligonucleotide reagents used in the testing

Information obtained by DNA-based HLA typing assays is more detailed and of higher quality than that obtained by conventional serological techniques. Nevertheless, it is common for data acquired in this way to be presented in the more familiar serological format. In many cases this representation can lead to significant loss of information, which may only become apparent at a later time, with the discovery of novel allele sequences. DNA-based typing methods, such as sequence-specific oligonucleotide probing (SSOP) or sequence-specific priming (SSP) generate fragmentary sequence data which is information rich. An alternative to assigning allele names to these fragments is to simply store the sequence data itself without interpretation. Bone marrow donor repositories can then be searched directly with sequence information, which though complex is more complete, rather than searching by derivative allele names.

Definition of peptide binding motifs amongst the HLA-A*30 allelic group

HLA class I molecules present endogenously processed peptide ligands for surveillance by the T-cell receptor. This potentially immunogenic surface of HLA and peptide is a consequence of the polymorphism found within the HLA molecule and its preference for ligand binding together with peptide conformation within the binding groove. To investigate the relation between the polymorphic differences between some closely related HLA alleles and their effect on peptide preference, transfectants were established, each containing one of four allelic variants of HLA-A*30. Peptides from all four transfectants were eluted, and both individual ligands and peptide pools were sequenced. The data shows two distinct peptide motifs which distinguish A*3001 from the other three known A*30 variants. Differences in preferences at minor positions within the peptide sequence were noted between A*3002, A*3003 and A*3004, providing additional evidence of the implications of sequence polymorphism to HLA function.

Update: the twenty subtypes of HLA-B27

HLA-B27 is a serologic specificity that encompasses 20 different alleles-HLA-B*2701 to B*2720. These alleles are also called subtypes of HLA-B27, and they have evolved from the B*2705 subtype, mostly from changes in exons 2 and 3 (which encode the alpha 1 and alpha 2 domains of the peptide binding groove, respectively). Occurrence of ankylosing spondylitis (AS) or related spondyloarthropathy (SpA) has thus far been documented in subjects possessing any one of the first 10 subtypes. However, B*2706 in Southeast Asian and B*2709 in the Italian island population of Sardinia may have a relatively much weaker association with AS. The 10 most recent subtypes have not yet been studied for disease association. There may exist a hierarchical ranking, resulting, in part, from differences in other co-inherited genetic factors, or due to environmental factors; eg, B*2705 is clearly disease-associated throughout the world, but not among the West Africans of Senegal and Gambia. It is important to investigate whether certain subtypes show any preferential association with some of the clinical features or forms of AS and related SpA among the various ethnic/racial populations and geographic regions of the world. This may help to identify the polymorphic positions of HLA-B27 that may have a disease-predisposing role.

Differential expression of human major histocompatibility class I loci: HLA-A, -B, and -C

Expression of the human class I MHC loci, HLA-A, -B, and -C, was examined by reverse transcription and competitive PCR with locus-specific primers. This approach allows unambiguous identification of target sequences by analysis of the amplified products. JY and Pala lymphoblastoid B cells express more HLA-A than HLA-B mRNAs and little HLA-C mRNA. Raji Burkitt lymphoma and HeLa carcinoma cells express approximately equal amounts of HLA-A and HLA-C mRNAs but less HLA-B mRNA. Jar trophoblast cells express no HLA class I mRNAs. Surprisingly, K562 leukemia cells express significant amounts of HLA-C mRNA. However, K562 cells contain no detectable HLA-A or -B mRNAs, suggesting that these loci are regulated independently. Furthermore, cultured endothelial cells and smooth muscle cells express low, approximately equal amounts of HLA-A, -B, and -C mRNAs, whereas donor-matched, EBV transformed B cells express much more HLA-B mRNA, suggesting that cell type dependent regulation underlies differential locus expression. Finally, expression of HLA class I molecules on the cell surface correlates with total HLA mRNAs but not with mRNAs encoded by any one locus. Differential expression of these HLA class I loci may contribute to cell-type dependent immune reactions by preferentially presenting distinct peptides to T cells.

Multiple genetic alterations cause frequent and heterogeneous human histocompatibility leukocyte antigen class I loss in cervical cancer

The nature and frequency of human histocompatibility leukocyte antigen (HLA) class I loss mechanisms in primary cancers are largely unknown. We used flow cytometry and molecular analyses to concurrently assess allele-specific HLA phenotypes and genotypes in subpopulations from 30 freshly isolated cervical tumor cell suspensions.Tumor-associated HLA class I alterations were present in 90% of the lesions tested, comprising four altered pheno/genotype categories: (a) HLA-A or -B allelic loss (17%), mostly associated with gene mutations; (b) HLA haplotype loss, associated with loss of heterozygosity at 6p (50%). This category included cases with additional loss of a (third) HLA-A or -B allele due to mutation, as well as one case with an HLA class I-negative tumor cell subpopulation, caused by a beta2-microglobulin gene mutation; (c) Total HLA class I antigen loss and retention of heterozygosity (ROH) at 6p (10%); and (d) B locus or HLA-A/B downregulation associated with ROH and/or allelic imbalance at 6p (10%). Normal HLA phenotypes and ROH at 6p were observed in 10% of the cases. One case could not be classified (3%). Altered HLA class I antigen expression occurs in most cervical cancers, is diverse, and is mainly caused by genetic changes. Combined with widespread tumor heterogeneity, these changes have profound implications for natural immunity and T cell-based immunotherapy in cervical cancer.

Routine HLA-B genotyping with PCR-sequence-specific oligonucleotides (PCR-SSO) detects eight new alleles: B*0807, B*0809, B*1551, B*3529, B*3532, B*4025, B*5304 and B*5508

This paper describes eight new alleles (B*0807, B*0809, B*1551, B*3529, B*3532, B*4025, B*5304 and B*5508) that have been found by routine HLA-B genotyping with sequence-specific oligonucleotides (SSOs). All of the new alleles have variations which cause changes in residues that occur within antigen binding pockets and T-cell recognition sites of the antigen. The new polymorphisms within these new alleles may affect the nature and specificity of peptide binding and cause differential T-cell activation, which may have an affect in transplantation.

IMGT/HLA database--a sequence database for the human major histocompatibility complex

The IMGT/HLA Database is a specialist database for sequences of the human major histocompatibility (MHC) system. It includes all the HLA sequences officially recognised and named by the WHO Nomenclature Committee for Factors of the HLA System. The database provides users with online tools and facilities for the retrieval and analysis of these sequences. These include allele reports, alignment tools and a detailed database of all source cells. The online IMGT/HLA submission tool allows the submission of both new and confirmatory allele sequences directly to the WHO Nomenclature Committee for Factors of the HLA System. The latest version (release 1.4.1, November 1999) contains 1,015 HLA alleles from over 2,270 component sequences derived from the EMBL/GenBank/DDBJ databases. From its release in December 1998 until December 1999 the IMGT/HLA website received approximately 100,000 hits. The database currently focuses on the human major histocompatibility complex but will be used as a model system to provide specialist databases for the MHC sequences of other species.

Unrelated donors selected prospectively by block-matching have superior bone marrow transplant outcome

Previous retrospective studies have demonstrated improved outcome in patients whose donors were matched for non-HLA markers in the MHC as well as for HLA genes. Forty patients receiving transplants from unrelated donors were typed prospectively for HLA and non-HLA markers. Non-HLA markers near HLA-B (beta-block markers) and in the DRB1 introns (delta-block markers) were used to assess MHC match between donors and recipient. Patients whose donors were matched at the beta- and delta-blocks had improved event free survival (63%) compared to patients whose donors were mismatched at one or both blocks (25%) (p < 0.05). Patients whose donors were matched at the beta-block had significantly less severe acute graft versus host disease (p < 0.05). In order to investigate the basis for improved outcome block matching was correlated with HLA matching as determined by DNA sequencing. Beta-block matching was highly correlated with matching for exons 2 and 3 of HLA-B but less so for HLA-C. Delta-block matching was highly correlated with matching for exon 2 of HLA DRB1. It is concluded that matching for non-HLA markers in the MHC improves matching for HLA genes. Further studies are required to determine whether matching for non-HLA markers improves outcome to a greater extent than matching for the HLA genes alone.

A novel HLA-A24 (A*2420) allele identified in the Atayal tribe of Taiwan

The Taiwan indigenous population groups are classified into different tribes according their linguistic classification and cultural anthropology. One of the tribes, the Atayal, showed a high frequency of A24 alleles by SSOP analysis. High-resolution sequencing based typing identified a A*2402 variant "A*2420" which was found in 6 unrelated individuals. High-resolution typing is required to identify HLA polymorphism in the Taiwanese minority groups.

Identification of the null HLA-A2 allele, A*0232N

We have identified a null HLA-A*02 allele, HLA-A*0232N, by using a combination of serology, flow cytometry, polymerase chain reaction using sequence-specific primers (PCR-SSP) and full-length sequencing. The null HLA-A2 allele was identified in an Asian individual originally typed by serology as an apparently homozygous HLA-A3, B51. Subsequent genotyping by PCR-SSP identified the genotype as HLA-A*0201, *0301, B*51, Cw*1402. The serological type and lack of detectable HLA-A2 was confirmed using monoclonal antibody typing reagents. Flow cytometry studies failed to identify any cell surface HLA-A2 expression on the patient's peripheral blood lymphocytes. Genotyping using a PCR-SSP set designed to detect null alleles revealed the mutation had not been previously described. Full-length sequencing of the allele identified an allele which was subsequently named HLA-A*0232N. This allele is identical to HLA-A*0201 except for a novel point mutation (T for C) at position 493 which creates a premature stop codon. The sequencing enabled the development of a monospecific A*0232N PCR-SSP reaction which was used to screen 973 DNA samples: no further examples of A*0232N were identified.

Identification of an HLA-B7 serological variant and its characterization by sequencing based typing

We have identified an HLA-B*07 variant allele, B*0716, in a Caucasoid cadaver kidney donor. The HLA class I type by polymerase chain reaction using sequence-specific primers (PCR-SSP) was A*01, 32; B*07, 08; Cw*07. Serological typing, using monoclonal and polyclonal anti-HLA antisera, gave disparate results for the B antigens. Monoclonal antibodies identified B7 and B8 antigens but polyclonal antisera recognised only the B8 antigen. PCR using sequencing based typing (PCR-SBT) confirmed the presence of both B*0703 and B*0801 alleles but with a mutation in one of the alleles. The HLA-B*07 allele was isolated by allele-specific PCR and was shown to have a mutation, G-->T, at 292 in exon 2. This mutation changes codon 74, which encodes aspartic acid (GAC) present in all previously identified B*07 alleles, to tyrosine (TAC) in the variant. The serological results suggest that codon 74 is a crucial part of a B7 antigen-specific epitope recognised by tissue typing polyclonal antisera.

Significant associations of HLA-B*5101 and B*5108, and lack of association of class II alleles with Behçet's disease in Italian patients

Behçet's disease has been known to be strongly associated with human leukocyte antigen (HLA) B51, one of the split antigens of HLA-B5. An increased incidence of HLA-B51 in the patient group has also been reported in an Italian population. Since the B51 antigen has been recently identified to comprise nine alleles, B*5101-B*5109, we performed HLA-B51 allele genotyping by the polymerase chain reaction-sequencing based typing (PCR-SBT) method as well as serological HLA-A and -B typing among 21 Italian patients with Behçet's disease in order to investigate whether there is any correlation of one particular B51-associated allele with Behcet's disease. In addition, HLA class II genotyping was performed by the PCR-restriction fragment length polymorphism (RFLP) method. As a result, only the phenotype frequency of the B51 antigen was found to be significantly increased in the patient group as compared to the ethnically matched control group by the corrected P-value analysis (71.4% in patients vs. 17.9% in controls; chi2 = 14.26, Pc = 0.0042, R.R. = 11.5). In the B51 allele genotyping, 11 out of 15 B51-positive patients were B*5101 and the remaining four were B*5108, whereas all of 5 normal controls were B*5101, showing significant association of each allele with Behçet's disease. No significant difference was observed between the patient and control groups in the HLA class II allelic distribution. This study revealed a strong association of Behçet's disease in Italian with B*5108 as well as B*5101, providing important insight into the molecular mechanism underlying an HLA association with Behçet's disease.

HLA-B*4021: hybrid linking the B15 and B40 families

Twenty alleles encoding molecules with the B60 or B61 serologic specificity have been reported thus far. This study characterized a new allele encoding a molecule exhibiting partial serologic reactivity with B15- and B40-related alloantisera from unrelated Korean individuals. Based on the DNA sequence, it appears that the novel allele has a sequence identical to some of alleles in B*15 family including B*1501 in exon 2. The sequence in exon 3, however, is identical to alleles in the B*40 family (B*4001/07/10/12) and B*4803. This implies that the novel allele, B*4021, has evolved by a reciprocal gene recombination involving members of these two families. The haplotype associated with B*4021 is likely to be A11-Cw4-B*4021-DRB1*04-DRB4*01-DQA1*03-DQB1*0301 .

Definition and transfer of a serological epitope specific for peptide-empty forms of MHC class I

Nascent class I molecules have been hypothesized to undergo a conformational change when they bind peptide based on the observation that most available antibodies only detect peptide-loaded class I. Furthermore recent evidence suggests that this peptide-facilitated conformational change induces the release of class I from association with transporter associated with antigen processing (TAP)/tapasin and other endoplasmic reticulum proteins facilitating class I assembly. To learn more about the structure of peptide-empty class I, we have studied mAb 64-3-7 that is specific for peptide-empty forms of L(d). We show here that mAb 64-3-7 detects a linear stretch of amino acids including principally residues 48Q and 50P. Furthermore, we demonstrate that the 64-3-7 epitope can be transferred to other class I molecules with limited mutagenesis. Interestingly, in the folded class I molecule residues 48 and 50 are on a loop connecting a beta strand (under the bound peptide) with the alpha(1) helix (rising above the ligand binding site). Thus it is attractive to propose that this loop is a hinge region. Importantly, the three-dimensional structure of this loop is strikingly conserved among class I molecules. Thus our findings suggest that all class I molecules undergo a similar conformational change in the loop around residues 48 and 50 when they associate with peptide.