Susceptibility to Reiter's syndrome is associated with alleles of TAP genes

An update on the contribution of the MHC to AS susceptibility

The 40-year-old association of HLA-B27 with ankylosing spondylitis is one of the best examples of disease association with a hereditary marker. Genomewide association and family studies suggest that other important major histocompatibility complex (MHC) influences are operative in ankylosing spondylitis (AS) susceptibility. HLA-B27 positive hepatitis C individuals are immunologically more efficient in combating viral infections such as HIV-1, hepatitis C, and influenza and less efficient in combating against certain bacteria (and perhaps other organisms) capable of surviving intracellularly. A recent representative population survey of the frequency of HLA-B27 in the USA found a lower frequency of HLA-B27 in older US adults, perhaps reflecting this. Other HLA class I and class II alleles have been implicated in AS susceptibility, the most consistent being HLA-B*40/B60 (B*40:01) but also B14, B15, A*0201, DRB1*04:04, and certain DPA1 and DPB1 alleles. Non-HLA MHC alleles have also been implicated, although many such studies have been inconsistent, likely due to power issues related to the low number of HLA-B27-negative AS patients examined. The best evidence is for major histocompatibility complex class I chain-related gene A (MICA) whose recognition by intestinal epithelial T cells expressing different V-delta-1 gamma/delta TCR further implicates the gut in AS pathogenesis. The HLA class I and class II and other non-HLA allelic associations underscore the importance of T cells in AS pathogenesis.

Characterization and allelic variation of the transporters associated with antigen processing (TAP) genes in the domestic dog (Canis lupus familiaris)

The function of the transporters associated with antigen processing (TAP) complex is to shuttle antigenic peptides from the cytosol to the endoplasmic reticulum to load MHC class I molecules for CD8(+) T-cell immunosurveillance. Here we report the promoter and coding regions of the canine TAP1 and TAP2 genes, which encode the homologous subunits forming the TAP heterodimer. By sampling genetically divergent breeds, polymorphisms in both genes were identified, although there were few amino acid differences between alleles. Splice variants were also found. When aligned to TAP genes of other species, functional regions appeared conserved, and upon phylogenetic analysis, canine sequences segregated appropriately with their orthologs. Transfer of the canine TAP2 gene into a murine TAP2-defective cell line rescued surface MHC class I expression, confirming exporter function. This data should prove useful in investigating the association of specific TAP defects or alleles with immunity to intracellular pathogens and cancer in dogs.

Genetic study confirms association of HLA-DPA1(∗)01:03 subtype with ankylosing spondylitis in HLA-B27-positive populations

The association of human leukocyte antigen (HLA)-B27 with ankylosing spondylitis (AS) has been known for over 38 years. However, it is not the only gene associated with AS. The aim of this study was to confirm the association of HLA markers around HLA-DPA1/DPB1 region with AS in HLA-B27 positive populations. Five SNPs (rs422544, rs6914849, rs92777535, rs3128968 and rs2295119) from the HLA-DPA1/DPB1 region were genotyped in 340 individuals HLA-B27-positive from Portugal (137 AS patients and 203 healthy controls). Characterizations of HLA-DPA1/DPB1 alleles were also performed. rs422544 revealed a significant association with AS (P<0.05) and sliding windows (SW) analysis showed association of some groups of adjacent SNPs within HLA-DPA1/DPB1 region with AS (P<0.05). We also found association of the HLA-DPA1(∗)01:03 allele with AS (P<0.05). This is the first study that confirms the association of HLA markers and haplotypes around HLA-DPA1 and HLA-DPB1 with AS.

Old and new HLA associations with ankylosing spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease that primarily involves the axial skeleton and the sacroiliac joint, but may also affect peripheral joints and entheses. AS susceptibility is clearly attributable to genetic factors and the link between human leukocyte antigen (HLA)-B27 and AS is the strongest association between an HLA class I molecule and a disease. However, there is evidence for the involvement of other, non-B27 factors within the major histocompatibility complex (MHC) in AS susceptibility. MHC class I is clearly the most significant genetic region for the disease, although most of the genetic association of this region is driven by HLA-B27. Moreover, several studies have investigated the MHC class II region and its association with AS. This review summarizes the current findings concerning the MHC genetics of the disease, focusing in particular on the associations of HLA with AS found in different ethnic populations throughout the world, and the possible mechanisms underlying them.

Determination of TAP1 and TAP2 polymorphism in the Chinese Han population by real-time TaqMan polymerase chain reaction

The heterodimeric transporter associated with antigen processing (TAP) complex plays a key role in immune surveillance. TAP1 and TAP2 typing was usually performed by polymerase chain reaction (PCR)-restriction fragment length polymorphism and PCR-sequence-specific oligonucleotide probe. As an alternative to these methods, we have established TaqMan assays to determine the frequencies of the TAP1 and TAP2 alleles. We have used these new TaqMan assays to genotype the polymorphisms in 339 unrelated Chinese Hans residing in North and South China. We detected five TAP1 and four TAP2 alleles. All the loci conform to the Hardy-Weinberg expectations. The most frequent alleles in Chinese Hans were TAP1*0101 (79.79%) and TAP2*0101 (82.74%). The two-locus haplotype analysis showed highly significant positive linkage disequilibrium for one TAP1-TAP2 haplotype (TAP1*020101-TAP2*0102), three TAP1-DRB1 haplotypes (TAP1*020101-DRB1*03, TAP1*020102-DRB1*13, and TAP1*0301-DRB1*16), and three TAP2-DRB1 haplotypes (TAP2*0102-DRB1*09, TAP2*0103-DRB1*04, and TAP2*0201-DRB1*01). The three-locus haplotype analysis showed highly significant positive linkage disequilibrium for TAP1*0101-TAP2*0101-DRB1*07, TAP1*0101-TAP2*0103-DRB1*04, TAP1*020101-TAP2*0101-DRB1*03, and TAP1*020101-TAP2*0102-DRB1*13. Comparison of the allele frequencies with those of other populations showed that the TAP1 allele distribution was very similar in all the groups, except for the Guarani, Kaingang, and Anatolian populations, but TAP2 distribution was significantly different from that of the other populations. The new TaqMan method provides relatively accurate, high-resolution, simple, and fast assays for TAP genotyping.

Association study between hypertension and A/G polymorphism at codon 637 of the transporter associated with antigen processing 1 gene

To explore the effect of A/G polymorphisms at codon 637 of the transporter associated with antigen processing 1 (TAP1) gene on the risk of hypertension. A case-control study of epidemiology was conducted. The case group included 277 community-based patients (136 males and 141 females; mean age 58.7+/-12.1 years) diagnosed with hypertension, and the control group consisted of 227 healthy subjects (95 males and 132 females; mean age 51.29+/-12.16 years) from the same community. The A/G polymorphisms at codon 637 of the TAP1 gene was examined by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method with genomic DNA. The effect of A/G polymorphisms at codon 637 of the TAP1 gene on hypertension was analyzed by using multivariate unconditional logistic regression models. The contribution of TAP1 637 A/G allele frequencies of the control group was consistent with that predicted by the Hardy-Weinberg equilibrium test (x2=230, p=0.632). There was a significant difference in the frequency of the A/G polymorphisms at codon 637 of the TAP1 gene between hypertensive patients (74.4/25.6%) and controls (82.4%/17.6%), x2=9.324, p=0.002. Genotype model (AA-AG-GG) analysis showed that there was a significant difference in the frequency of the recessive genotype between cases and controls (AA/AG vs. GG: odds ratio [OR]=3.046, 95% confidence interval [CI]=1.138-8.153) after adjustment for the covariates of age, serum total cholesterol, triglycerides, body mass index (BMI) and smoking. But there were no significant differences in the frequency of the genotype for the dominant model (AA vs.

AG/GG

p=0.293) or additive model (AA vs. AG vs. GG: p=0.081) after adjustment. One-way ANOVA analysis showed that the systolic blood pressure, diastolic blood pressure, and BMI levels of the GG genotype were significantly higher than those of the AA or AG genotypes. In conclusion, our findings suggest that the A/G polymorphisms at codon 637 of the TAP1 gene contributes to the risk of hypertension, possibly via the increases in blood pressure and BMI.

The genetic basis of ankylosing spondylitis

PURPOSE OF REVIEW

Genetic factors provide over 90% of the overall susceptibility to ankylosing spondylitis, with about half of the genetic contribution attributed to HLA-B27 and other major histocompatibility complex genes. Recent studies have focused on non-major histocompatibility complex genes. This review is aimed at summarizing the status of major histocompatibility complex and non-major histocompatibility complex genes in ankylosing spondylitis susceptibility, and suggests areas for future studies.

RECENT FINDINGS

A recent meta-analysis of published scans of ankylosing spondylitis susceptibility has confirmed sites on chromosomes 3q, 6p (the major histocompatibility complex), 10q, 16q and 19q in ankylosing spondylitis susceptibility. Non-major histocompatibility complex candidate gene analyses have confirmed a role for the IL-1 gene complex. The search for other non-major histocompatibility complex candidate genes, however, has been complicated by inadequate power in most previous studies. Innovations in genetic methodologies will allow thorough genome wide linkage disequilibrium mapping studies in large cohorts of patients that will result in the dissection of the genetic susceptibility to ankylosing spondylitis.

SUMMARY

Nearly half of the susceptibility to ankylosing spondylitis is provided by major histocompatibility complex genes. Non-major histocompatibility complex genes, most notably the IL-1 gene complex, have been identified and novel technologies promise that a more thorough examination of the rest of the genome will soon elucidate the genetic basis of this disease.

Association between the TAP2 gene codon 665 polymorphism and Graves' disease

A total of 95 patients with active Graves' disease (GD) and 105 normal healthy subjects were enrolled in this study, which attempted to determine whether single-site polymorphisms of the transporter associated with antigen processing 2 (TAP2) gene contribute to an individual's susceptibility to GD. Such polymorphisms were detected using polymerase chain reaction (PCR)-based restriction analysis. Associations between GD and the three site polymorphisms of the TAP2 gene at codons 379, 565, and 665 were investigated. The results of the genotype analysis revealed that the frequency of the GG homozygote's presence at codon 665 was lower, and that of the AA homozygote's presence was greater in GD patients (15.8% and 36.8%, respectively) compared to normal controls (34.3% and 16.2%, respectively; P<0.001). The OR (OD) for the risk of occurrence for the AA homozygote and AG heterozygote compared to the GG homozygote (as was the case for the GD patients) was respectively 4.941 and 2.117, with respective 95% confidence intervals (CI) of 2.303-10.598 and 1.020-4.369. The allelic analysis also demonstrated reduced G and enhanced A allele frequencies for GD patients compared to controls (respectively 39.5% vs. 59.0% [G allele], and 60.5% vs. 41.0% [A allele]; P=0.0001; OR=2.219, 95% CI: 1.449-3.395). By contrast, the differences between patient and control groups for the frequency of appearance of genotypes and allelic variants at codon 379 (P=0.522 and P=0.306, respectively) and codon 565 (P=0.199 and P=0.157, respectively) did not appear to be significant. These data reveal that the single-site polymorphism of the TAP2 gene at codon 665 may be an indicator for predicting GD development.

Association of TAP1 and TAP2 Gene Polymorphisms With Systemic Sclerosis in Korean Patients

We sought to determine whether transporter associated with antigen processing (TAP) gene polymorphism is associated with susceptibility to systemic sclerosis (SSc). TAP1 and TAP2 gene polymorphisms were analyzed in 61 Korean patients with SSc and 100 ethnically matched healthy Koreans by polymerase chain reaction-restriction fragment length polymorphism. Human leukocyte antigen (HLA)-DRB1 genotyping data of the patients from our previous study was used for the assessment of independent role of TAP genes to SSc susceptibility. Patients were stratified according to anti-topoisomerase I (anti-topo I) antibody status and clinical subsets of diffuse and limited cutaneous SSc (dcSSc and lcSSc). TAP1 and TAP2 gene polymorphisms were associated with different subsets of SSc: TAP1*A/A genotype with anti-topo I-positive dcSSc (p = 0.01, p corrected = 0.04), TAP2*A1/C genotype with anti-topo I-positive lcSSc (p < 0.05), TAP2*Bky2 and *C alleles with anti-topo I-negative dcSSc (both p < 0.05), and TAP2*B/E genotype with anti-topo I-negative lcSSc (p = 0.004). Although TAP gene associations were generally weak, some associations (TAP2*A1/C, TAP2*C, and TAP2*B/E) with different subsets of SSc were independent of HLA-DR associations, revealing even stronger associations (TAP2*A1/C and TAP2*C) among individuals not possessing the risk HLA-DR alleles. These results suggest the possible role of TAP gene polymorphisms in the genetic susceptibility to SSc.

No association of TAP2 polymorphisms in Korean patients with schizophrenia

OBJECTIVES

Polymorphisms of transporters associated with antigen-processing (TAP) genes might influence the susceptibility to schizophrenia by altering the antigen-processing pathway. The aim of this study was to verify the relationship between schizophrenia and the polymorphisms of TAP2 genes.

METHOD

Two hundred and fifty-seven Korean patients diagnosed with schizophrenia according to DSM-IV and 184 normal controls participated in this study. TAP2 polymorphic residues at positions 379, 565 and 665 were typed using amplification refractory mutation system-polymerase chain reaction single-strand conformation polymorphism.

RESULTS

Distribution of the alleles and genotypes in patients with schizophrenia was not significantly different from those of controls.

CONCLUSIONS

This study did not show the association of the TAP2 gene with schizophrenia in the Korean population.

Variation in vaccine response in normal populations

Genetic polymorphisms of the human leukocyte antigen (HLA) system significantly influence the variation in immune responses to viral vaccines. Considerable data on the genetic determinants of immune responses to the measles vaccine support the importance of HLA genes in determining the variation in vaccine response. HLA class I and class II, TAP, and HLA-DM allele associations with measles-specific antibody levels following measles vaccination have revealed, in part, the immunologic basis for mechanisms of measles immunity variation. Associations between HLA genotype and immune responses have also been reported for other vaccines and infectious diseases, such as hepatitis B and C, human papillomaviruses, and influenza. Vaccine pharmacogenomics may provide important insights for the design and development of new peptide-based vaccines against measles and other pathogens.

Novel TAP1 polymorphisms in indigenous Zimbabweans: their potential implications on TAP function and in human diseases

Because of the essential role of transporter associated with antigen processing (TAP1 or TAP2) molecule in antigen processing, the implication of its polymorphism as a factor involved in human diseases and the possible genetic variation at this locus among ethnically diverse populations, we underwent a study to analyze the full extent of TAP1 polymorphism in an indigenous Zimbabwean population (Shona ethnic group). Using single-stranded conformation polymorphism and DNA direct sequencing procedures, we detected the presence of 11 nucleotide sequence variations in the entire coding region of TAP1. Of these variants, eight are nonconservative substitutions with respect to amino acid composition and are located in a critical part of the protein that could modulate its function. Five new polymorphic sites were identified in exon 1 (codons 7 Pro --> Ser, 17 Gly --> Arg, 141 Val --> Val), exon 6 (codon 419 Gly --> Cys), and exon 7 (codon 487 Arg --> Arg). Significant differences were seen in the distribution of TAP1*0201 and TAP1*0401 alleles, and codon 333 (Ile --> Val) polymorphism among African and non-African populations. Thus, TAP1 polymorphism has evolved differently among populations presumably because of the evolutionary pressures generated by prevalent pathogens in these geographically distinct regions.

New transporter associated with antigen processing (TAP-2) polymorphisms in the Shona people of Zimbabwe

Most studies, to date, on transporter associated with antigen processing (TAP2) polymorphism have been conducted in Caucasians or Asians from industrialized countries. Because of the essential role of this molecule in antigen processing, the implication that polymorphism could be a major factor in human disease and the possible genetic variation at this locus among ethnically diverse populations, we undertook a study to analyze the full extent of TAP2 polymorphism in an indigenous Zimbabwean population (Shona ethnic group). Using single-stranded conformation polymorphism and DNA direct sequencing procedures, we detected the presence of 17 nucleotide sequence variations in the entire coding region of TAP2. Of these variants, 11 are nonconservative substitutions with respect to amino acid composition and are located in a region of the protein that could modulate its function. Six new polymorphic sites were identified in exon 1 (codons 15 Val-->Ala, 53 Leu-->Val), exon 3 (codon 220 Arg-->Arg), exon 4 (codons 257 Thr-->Ile, 313 Arg-->His), and exon10 (codon 609 Ala-->Val). Significant differences were seen in the distribution of the known 374Thr, 565Thr and 651Cys variants between African and non-African populations. These differences may reflect evolutionary pressures generated by environmental factors, such as prevalent pathogens in these geographically distinct regions. Further studies are needed to elucidate the net impact of TAP2 polymorphism on the protein's function and it's role in disease pathogenesis.

Frequencies of TAP1 and TAP2 gene polymorphisms in the Anatolian population

Anatolia has a long and complex record of immigration from various regions. Here, we have used TAP1 and TAP2 gene polymorphisms as genetic markers to study the relationship between the Anatolian population and other populations. A neighbour-joining tree was constructed indicating the relatedness of European populations and the Anatolian population with respect to TAP1 and TAP2 allele frequencies.

Polymorphisms of human TAP2 detected by denaturing gradient gel electrophoresis

The human transporter associated with antigen processing (TAP1 and TAP2) genes are located in the human leukocyte antigen (HLA) class II region of the genome and encode proteins that form a heterodimer essential for the transport of endogenous peptides into the endoplasmic reticulum for assembly with HLA class I molecules. Type 1 diabetes is an autoimmune disease that is associated with the HLA region of the genome, with HLA class II genes conferring the greatest statistical risk. The presentation of self-peptides by HLA class I molecules is defective in individuals with this disease, and both TAP1 and TAP2 are potential contributors to this defect. Denaturing gradient gel electrophoresis (DGGE) was applied to screen all 11 exons and the 3' flanking region of TAP2 for polymorphisms in individuals with type 1 diabetes patients and controls. Seventy polymorphisms, including 51 in introns, 4 in the 3' flanking region, and 15 in exons, were identified. Sequencing of polymorphic DNA fragments revealed several new polymorphisms, including a Gln --> Arg substitution at codon 611 and a GT --> GC polymorphism affecting the donor splice site of intron 4, that might be of functional significance. None of the polymorphisms examined differed in frequency between individuals with type 1 diabetes and controls.

Genetics of susceptibility to leprosy

The ancient disease of leprosy can cause severe disability and disfigurement and is still a major health concern in many parts of the world. Only a subset of those individuals exposed to the pathogen will go on to develop clinical disease and there is a broad clinical spectrum amongst leprosy sufferers. The outcome of infection is in part due to host genes that influence control of the initial infection and the host's immune response to that infection. Identification of the host genes that influence host susceptibility/resistance will enable a greater understanding of disease pathogenesis. In turn, this should facilitate development of more effective therapeutics and vaccines. So far at least a dozen genes have been implicated in leprosy susceptibility and a genome-wide linkage study has lead to the identification of at least one positional candidate. These findings are reviewed here.

Distribution of TAP gene polymorphisms and extended MHC haplotypes in Mexican Mestizos and in Seri Indians from northwest Mexico

The study of the genetic structure is very useful for investigating the biological significance of polymorphism and may provide clues to understand population origins. We present TAP1/TAP2 gene analysis in the Seri indians from Sonora, and in Mestizos from the highlands of Mexico. Thirty-two Seri and 89 Mestizos were studied. TAP genes were typed using the ARMS-PCR technique. The most frequent alleles in Seri were: TAP1*0101/02, (68.8%); TAP1*02011/02012, (31.2%); TAP2*0201, (38.7%) and TAP2*0101, (29.0%). TAP1*0301, TAP1*0401, TAP2*0102 TAP2*0103 and TAP2H were absent in them. For Mestizos, the prevalent alleles were: TAP1*0101/02 (75.8%); TAP1*02011/12 (20.3%); TAP2*0101 (45.4%) and TAP2*0201 (29.3%). These results are similar to those found in Kaingang and Caucasians from Brazil, four Mediterranean, other Caucasians, two Oriental and one African group. In Seri, the extended prevalent haplotypes are typically Amerindian, such as TAP1*0101/2-TAP2*0201-QBP3.21-DQB1*0302-QAP*3.1-DQA1*03011-DRB1*0407-B*3501-A*0201 (HF = 16.6%). Thirty-two extended haplotypes were found in Seri, although TAP contributed scarcely to diversity. Mestizos show Amerindian and Caucasian combinations. No difference was detected in the distribution of amino acids in the individual variable sites, between both groups. These findings are the basis for further anthropological studies and to explore the contribution of TAP genes to disease expression in Mexicans.

Analysis of TAP2 polymorphisms in Finnish individuals with type I diabetes

Type I diabetes mellitus is an immune-mediated disease that is known to be associated and linked with genes in the human leukocyte antigen (HLA) region on chromome 6. Functionally, HLA class I antigen presentation may be deranged in type I diabetes. The TAP1 and TAP2 transporters, which mediate the translocation of antigenic peptides into the endoplasmic reticulum and whose genes are located in the HLA class II region, are potential candidates for conferrring predisposition to type I diabetes. Five known coding region variants (codons 379, 565, 651, 665, and 687) as well as three new polymorphisms of TAP2, one silent (codon 604) and two intronic (nucleotide positions 49,270 and 49,471), were typed in a cohort of 146 well-characterized Finnish individuals with type I diabetes and 90 control subjects. Absolute linkage disequilibrium was apparent for the polymorphisms at codons 604, 665, and 687 as well as the two downstream intronic polymorphisms in a 613-bp region of the 3' portion of TAP2; the polymorphism at codon 651, which is also present within this region, was excluded from this linkage. The codon 651 polymorphism defines the allele TAP2F, the frequency of which in HLA-DR4+ diabetic subjects was 5.4 times that in DR4+ controls (27 vs. 5%, p = 0.002, p(c) = 0.01). These data are consistent with the existence of susceptibility haplotypes for type I diabetes in the Finnish population consisting of DRB1*04 (*0401 and *0404), DQ8, and TAP2F.

Spontaneous inflammatory disease in HLA-B27 transgenic mice does not require transporter of antigenic peptides

HLA-B27 is strongly linked with a group of human diseases called spondyloarthropathies. Even though HLA-B27 as an MHC class I molecule would be expected to present endogenously processed peptides such as cytosolic or viral proteins, many of the B27-linked diseases begin after an infection with an enterobacteria, an exogenous antigen. In our previous studies, we have described development of spontaneous inflammatory disease in HLA-B27 transgenic mice expressing beta(2)m free heavy chains on the cell surface. In order to address the role of endogenous versus exogenous antigens and a role for Tap genes in the development of spontaneous diseases, mice lacking Tap-1 (knockout) were mated to HLA-B27/human beta(2)m transgenic mice. B27(+)/human beta(2)m(+) double-transgenic mice (without mouse beta(2)m) lacking the Tap-1 gene developed spontaneous inflammatory disease similar to wild-type Tap-1 gene-expressing counterparts. Our data demonstrate that peptide transporters (Tap) were not involved in the development of spontaneous inflammatory disease in B27(+)/human beta(2)m transgenic animals.

Polymorphism of LMP2, TAP1, LMP7 and TAP2 in Brazilian Amerindians and Caucasoids: implications for the evolution of allelic and haplotypic diversity

In the class II region of the major histocompatibility complex (MHC), four genes implicated in processing of MHC class I-presented antigens have been described. Two of these (TAP1 and TAP2) code for endoplasmic reticulum membrane transporter proteins and the other two (LMP2 and LMP7) for proteasome subunits. These genes are polymorphic, although much less so than classical MHC class I and II genes. There is controversy concerning the possible functional implications of this variation. Population genetics is one of the means of investigating the evolutionary and functional significance of genetic polymorphisms; however, few populations have been analysed with respect to TAP and LMP diversity. We present here the polymorphism of TAP1, TAP2, LMP2 and LMP7 genes in the Kaingang and Guarani Amerindian tribes, and in the Caucasoid population of the Brazilian State of Paraná. Allele frequencies found in the Caucasoids were close to those described for similar populations. Amerindians had a somewhat more restricted polymorphism, and allele and haplotype frequencies differed greatly between the two tribes. Overall linkage disequilibrium (LD) between the four genes was low in the Caucasoids, but high in the Amerindians, for which significant LD was seen for all informative pairs of loci. Comparing results of this and previous studies we observed that, whenever significant LD occurs in non-Amerindians, it tends to be similar in the different ethnic groups. While this might be interpreted as evidence of co-evolution of genes in the TAP-LMP region, the high haplotypic diversity in all populations and low LD in non-Amerindians indicate absence of co-evolution of the different genes. Distributions of allele and genotype frequencies are consistent with the hypothesis of selective neutrality. We conclude that genetic polymorphism of the human TAP and LMP genes and haplotypes is of little, if any, functional significance.

The immunogenetics of the seronegative spondyloarthropathies

In none of the rheumatic diseases has the genetic contribution to pathogenesis been so well characterized as in the seronegative spondyloarthropathies. Most important has been the elucidation of the structure and effect on disease expression of HLA-B27, where 11 subtypes have been distinguished to date. These vary in frequency in different ethnic groups and seem to show differential disease associations. The high frequency of this gene in patients with the seronegative spondyloarthropathies, especially ankylosing spondylitis (AS) and Reiter's syndrome (RS)/reactive arthritis (ReA), has emerged as probably the best example of a disease association with a hereditary marker. Other HLA genes, in addition to HLA-B27, have been implicated in psoriasis and psoriatic arthritis. These include those from the HLA-C locus and from HLA-DR. In addition, recent family studies have implicated other genes outside the MHC that further enhance the susceptibility to AS.

Animal models of human leukocyte antigen B27-linked arthritides

The major histocompatibility complex class I allele human leukocyte antigen (HLA) B27 is strongly associated with human spondyloarthropathies. To date, 12 subtypes of HLA-B27 are known and most of them are linked with human spondyloarthropathies in different ethnic populations. Although these subtypes differ from each other by a few amino acids, the have an identical B pocket in the base of the antigen-binding groove. Considering the structure of HLA-B27 subtypes and their peptide binding specificity, it is important to consider their role as antigen-presenting molecules. Many B27-linked diseases begin after an infection with an enterobacteria, suggesting a role for environmental antigens in addition to an HLA-B27 molecule. To delineate the role of infection, studies have been carried out in animal models of reactive arthritidis. More recently, transgenic animal models have been used to understand the handling of environmental antigens by HLA-B27 molecule. This article discusses some of these transgenic and nontransgenic animal models of human diseases.

TAP1 polymorphism identified in African-American Graves' disease patients

Polymorphism in transporter associated with antigen processing (TAP)1 gene has been observed in African American Graves' disease patients. Single strand conformational polymorphism has been used to identify variation for the locus. First-strand cDNA was generated from cell lines obtained by Epstein-Barr virus immortalization. Four variant alleles for TAP1 have been observed and the products have been sequenced to compare with the location of observed with SSCP position patterns. Variants were detected and compared with substitutions within TAP1 polypeptide which includes changing valine to leucine and three (3) silent substitutions for glycine, glutamic acid and alanine.

Association of a new allele of the TAP2 gene, TAP2*Bky2 (Val577), with susceptibility to Sjögren's syndrome

OBJECTIVE

To investigate the polymorphisms of TAP (transporters associated with antigen processing) genes among patients with primary Sjögren's syndrome (SS) in order to clarify the potential association of the polymorphisms with disease susceptibility.

METHODS

Polymorphisms of the TAP1 and TAP2 genes in 108 Japanese SS patients were determined by analyzing TAP genes using the polymerase chain reaction-single-stranded conformation polymorphism technique.

RESULTS

The allelic frequency of the TAP1 gene was not significantly different between SS patients and normal subjects. In addition to all known TAP2 alleles, a new allele (Bky2), which had a unique substitution at codon 577 (ATG-->GTG: Met-->Val), was identified in both groups. The allelic frequency of Bky2 was significantly higher in SS patients (12.0%) than in normal subjects (5.1%) (P < 0.05). Moreover, a significantly greater frequency of SS-A antibody was found among SS patients with Bky2 (18 of 23; 78%) than among those without Bky2 (33 of 85; 39%) (P = 0.001).

CONCLUSION

The mutation in TAP2 (Val577) may be involved in SS-A autoantibody production and could be a genetic factor that determines susceptibility to SS.

Increase of HLA-DRB1*0408 and -DQB1*0301 in HLA-B27 positive reactive arthritis

OBJECTIVE

To study HLA class II association in reactive arthritis.

METHODS

63 patients with reactive arthritis and 46 with rheumatoid arthritis were included in the study. HLA-DR alleles were determined by using a sequence specific PCR method. Oligonucleotide hybridisation was used for definition of DRB1*04 subtypes and DQB1 alleles. HLA-B27 was determined by standard microcytotoxity test or by PCR. HLA-B27 subtyping was made by sequencing.

RESULTS

46 (73%) of 63 patients with reactive arthritis were HLA-B27 positive and 24 (38%) were HLA-DRB1*04 positive. When haplotypes were inferred according to the known associations between DRB1 and DQB1 alleles, the frequency of DRB1*04-DQB1*0301 haplotype was found to be 13% (12/92) in HLA-B27 positive reactive arthritis patients, in contrast to 0% in HLA-B27 negative reactive arthritis (P = 0.04) and 1% in random controls (P = 0.0009). However, this combination was also found in 5% of 84 HLA-B27 positive control haplotypes, showing a linkage disequilibrium between B27 and this particular class II haplotype. HLA-DRB1*0408 subtype was found in 8/24 (33%) of the HLA-DRB1*04 alleles in patients with reactive arthritis, accounting for most DQB1*0301 haplotypes, but only in 5/55 (9%) of the DRB1*04 alleles in random controls (P = 0.017). All reactive arthritis patients with this subtype were positive for HLA-B27. DRB1*04-DQB1*0302 haplotype was increased in patients with rheumatoid arthritis (28/92, 30%) compared with reactive arthritis (12/126, 10%) or with the controls (12/100, 12%; P = 0.003). HLA-B*2705 was by far the dominant B27 subtype both in reactive arthritis patients with the particular DRB1*0408-DQB1*0301 haplotype and in controls. It was found in 11 out of 12 DR analysed patients, as well as in 10 out of 11 randomly selected B27 positive controls.

CONCLUSIONS

Although no single class II allele was found to be increased among patients with reactive arthritis, HLA-B27, DRB1*0408, and DQB1*0301 might exert a haplotypic effect in the pathogenesis of reactive arthritis, or they may be markers of a subset of B27 haplotypes conferring susceptibility.

Polymorphisms of TAP1 and TAP2 genes in Graves' disease

Graves' disease is an autoimmune disorder in which HLA DQA1*0501 and DQB1*0201 confer predisposition. The genes for transporters associated with antigen processing (TAP1 and TAP2) locate near to HLA DQ coding regions and display only a limited degree of polymorphism. Since polymorphisms of TAP might influence susceptibility to Graves' disease by a possibly different selection of antigenic peptides, we investigated sequence variants of TAP1 and TAP2 genes in 235 patients with Graves' disease and 218 random healthy controls by polymerase chain reaction (PCR) followed by sequence specific oligonucleotide analysis (SSO), single strand conformational polymorphism (SSCP) analysis and amplification refractory mutation system (ARMS). TAP1*0301 (Val-333/Asp-637: 71% vs. 55% in controls, p < 0.008, RR = 2.05) and TAP2*0101 (Val-379/Ala-565/Thr-665/stop-687: 83% vs. 69% in controls, p < 0.03, RR = 2.20) showed a positive association with Graves' disease whereas TAP1*0401 a negative (Ile-333/Gly-637: 4% vs. 13% in controls, p < 0.01, RR = 0.25). After selection of patients and controls for HLA DQA1*0501 a similar association was found for TAP1*0301 (72% vs. 50% in controls, p < 0.02, RR = 2.63) and TAP1*0401 (4% vs. 16% in controls, p < 0.04, RR = 0.22), when matching for HLA DQB1*0201 as well as for TAP1*0401 (3% vs. 16% in controls, p < 0.05, RR = 0.18). Our findings indicate that the positive association of TAP1*0301 and the negative of TAP1*0401 with Graves' disease cannot only be explained by linkage disequilibrium between TAP alleles and HLA DQ. Therefore, these TAP alleles contribute to genetic susceptibility in Graves' disease as additional permissive and protective factors.

Specificities of human TAP alleles for HLA-B27 binding peptides

OBJECTIVE

Allelic TAP polymorphism has been linked to susceptibility to Reiter's syndrome and was suggested to influence disease phenotype in HLA-B27 positive patients with ankylosing spondylitis. In the present study, we examined whether the human TAP alleles functionally differ in their translocation specificity for HLA-B27-binding nonamers.

METHODS

TAP translocation of a panel of HLA-B27-binding peptides was measured with a labeled reporter peptide containing an N-linked glycosylation acceptor site in streptolysin O-permeabilized cells with different TAP alleles.

RESULTS

The different human TAP alleles tested did not measurably differ in their peptide specificity.

CONCLUSION

The polymorphism of human TAP does not affect the translocated repertoire of HLA-B27 ligands and is therefore unlikely to play a decisive role in the development of HLA-B27-associated disease.

Molecular mechanisms of class I major histocompatibility complex antigen processing and presentation

The presentation of antigenic peptides by class I major histocompatibility complex molecules plays a central role in the cellular immune response, since immune surveillance for detection of viral infections or malignant transformations is achieved by CD8+ T lymphocytes which inspect peptides, derived from intracellular proteins, bind to class I molecules on the surface of most cells. The transporter associated with antigen processing selectively translocates cytoplasmically derived peptides of appropriate sequence and length into the lumen of the endoplasmic reticulum where they associate with newly synthesized class I molecules. The translocated peptides are generated by multicatalytic and multisubunit proteasomes which degrade cytoplasmic proteins in a ATP-ubiquitin-dependent manner. This review discusses our current molecular understanding of class I antigen processing and presentation.

Reactive arthritis in patients attending an urban sexually transmitted diseases clinic

OBJECTIVE

To assess the prevalence, clinical manifestations, associated genital infections, and HLA associations of reactive arthritis (ReA) among patients attending an urban sexually transmitted diseases (STD) clinic.

METHODS

Using a standardized questionnaire, 271 consecutive adults, primarily black, with possible or proven Chlamydia trachomatis genital infection were screened for symptoms of ReA. A followup questionnaire was administered 6 weeks later by mail. Patients who reported at least 1 symptom were evaluated by a rheumatologist. HLA-B typing was performed on patients with objective ReA features.

RESULTS

Nine of 217 patients (4.1%) with genital infection/inflammation had objective ReA features. Chlamydial or nongonococcal STD syndromes were diagnosed in 8 of these 9 patients (88%). Genital infection/inflammation was asymptomatic in 78% of patients with ReA features. HLA-B27 or other B7-cross-reactive group antigens were not associated with the occurrence of ReA.

CONCLUSION

Nongonococcal genital infections, often asymptomatic, can trigger a relatively mild ReA in a larger number of exposed patients than previously thought, irrespective of the individual's HLA status.

A comparative study of HLA genes in HLA-B27 positive ankylosing spondylitis and HLA-B27 positive peripheral reactive arthritis

OBJECTIVE

To determine whether HLA-B27 positive patients with ankylosing spondylitis (AS) and reactive arthritis (ReA) share additional HLA factors that confer disease susceptibility.

METHODS

HLA class I antigens were typed serologically, and class II antigens molecularly, in samples taken from 33 patients with AS, 30 patients with ReA, and 55 healthy HLA-B27 positive controls.

RESULTS

There was no major difference between the HLA alleles in AS and ReA patients, but deviations were observed when compared with healthy controls, especially between the antigens that were probably encoded by genes in the non-B27 chromosome.

CONCLUSION

These results suggest that both HLA class I and class II genes may influence the pathogenesis of HLA-B27 positive ReA, whereas class I antigens seem to be the major additional genetic factors in HLA-B27 positive AS.