TAP2 association with insulin-dependent diabetes mellitus is secondary to HLA-DQB1

Significant association between TAP2 polymorphisms and rheumatoid arthritis: a meta-analysis

Background

Rheumatoid arthritis (RA) is a severe chronic immune mediated inflammatory disease that has been shown to be associated with human leukocyte antigen (HLA) loci. The transporter associated with antigen processing 2 (TAP2) has been identified to play an important role in the HLA-associated diseases and immune response. The goal of our meta-analysis was to summarize the contribution of TAP2 polymorphisms to the risk of RA.

Methods

Meta-analyses were performed between RA and 3 TAP2 coding polymorphisms that comprised TAP2-379Ile > Val (rs1800454), TAP2-565Ala > Thr (rs2228396) and TAP2-665Thr > Ala (rs241447). The meta-analyses were involved with 9 studies (24 individual studies) among 973 cases and 965 controls.

Results

Meta-analyses showed that TAP2-379Ile allele was significantly associated with an increased risk of RA (p = 0.0002, odds ratio (OR) = 1.44, 95% confidence interval (CI) = 1.18-1.74). This association was further shown only in the dominant model (p = 0.006, OR = 1.59, 95% CI = 1.14-2.22). Subgroup analyses by ethnicity revealed that the association of TAP2-379Ile was significant in Asians (p = 0.03, OR = 1.38, 95% CI = 1.04-1.83). In addition, another significant association of TAP2-565Thr allele with RA was observed in Europeans (p = 0.002, OR = 1.62, 95% CI = 1.20-2.20).

Conclusions

Our meta-analyses suggested that TAP2-379Ile allele was significantly associated with a 59% increased risk in the dominant effect model. Subgroup analyses by ethnicity showed that TAP2-379-Ile increased the risk of RA by 38% in Asians and TAP2-565Thr increased the risk of RA by 38% in Europeans.

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2097080313124700

TAP1 I333V gene polymorphism and type 1 diabetes mellitus: a meta-analysis of 2248 cases

Transporter associated with antigen processing 1 (TAP1) I333V gene polymorphism has been suggested to be associated with type 1 diabetes mellitus (T1DM) susceptibility. However, the results from individual studies are inconsistent. To explore the association of TAP1 I333V gene polymorphisms with T1DM, a meta-analysis involving 2246 cases from 13 individual studies was conducted. The pooled odd ratios (ORs) and their corresponding 95% confidence intervals (95% CIs) were evaluated by a fixed-effect model. A significant relationship was observed between TAP1 I333V gene polymorphism and T1DM in allelic (OR: 1.35, 95% CI: 1.08–1.68, P = 0.007), dominant (OR: 1.462, 95% CI: 1.094–1.955, P = 0.010), homozygous (OR: 1.725, 95% CI: 1.082–2.752, P = 0.022), heterozygous (OR: 1.430, 95% CI: 1.048–1.951, P = 0.024) and additive (OR: 1.348, 95% CI: 1.084–1.676, P = 0.007) genetic models. No significant association between TAP1 I333V gene polymorphism and T1DM was detected in a recessive genetic model (OR: 1.384, 95% CI: 0.743–2.579, P = 0.306) in the entire population, especially among Caucasians. No significant association between them was found in an Asian or African population. TAP1 I333V gene polymorphism was significantly associated with increased T1DM risk. V allele carriers might be predisposed to T1DM susceptibility.

TAP1 and TAP2 gene polymorphisms in Korean patients with allergic rhinitis

Antigen peptides are actively transported across the endoplasmic reticulum by the transporters associated with antigen presentation (TAP). TAP genes polymorphism could influence the selection process that determines which antigen peptides play a role in the pathogenesis of allergic rhinitis. The aim of this study was to investigate the association of TAP genes polymorphism with allergic rhinitis. TAP1 and TAP2 genotyping were performed on 110 allergic rhinitis patients and 107 healthy controls. TAP1 polymorphic residues at codons 333 and 637, and TAP2 polymorphic residues at codons 379, 565, 651, and 665 were analyzed by the amplification refractory mutation system-polymerase chain reaction (ARMS-PCR). Analysis of TAP1 gene polymorphism demonstrated decreased frequencies of Ile/Val genotype at codon 333, Asp/Gly genotype at codon 637, and haplotype A and B in allergic rhinitis patients when compared to controls (p<0.05). However, there was no significant difference in the genotype, phenotype, or allele frequencies at four TAP2 codons between controls and allergic rhinitis patients. In conclusion, TAP1 gene polymorphism may be an important factor contributing to the genetic susceptibility in the development of allergic rhinitis in the Korean population.

Pemphigus vulgaris is associated with the transporter associated with antigen processing (TAP) system

Pemphigus vulgaris (PV) is a human leukocute antigen (HLA) class II-associated autoimmune disease of the skin of unknown etiology. We recently described the association of pemphigus vulgaris with two clusters of microsatellite loci within the major histocompatibility complex region. One cluster includes the microsatellite marker TAP1CA, located in proximity to the transporter associated with antigen processing (TAP) genes. These genes are essential for class I antigen processing machinery and could be an additional set of genes involved in susceptibility to PV. The aim of this study was to investigate a possible association between TAP gene polymorphisms and PV. For this purpose we examined 37 unrelated Jewish Israeli patients with PV and compared them with 37 healthy Israeli Jewish HLA-matched controls. Significant differences were detected in TAP2 amino acid residues (p=0.001). Two PV TAP2 risk alleles were identified (TAP2*C and TAP2*D), the frequency of which was estimated to be 37.8% in the patients and 5.3 % in the controls. This association was found to be independent of HLA-DR. It is therefore likely that TAP2 genes are involved in susceptibility to development of PV.

Genetic susceptibility to type 1 diabetes in the intracellular pathway of antigen processing - a subject review and cross-study comparison

Ligand binding grooves of MHC class I molecules are able to load a panel of endogenous peptides of varying length and sequence derived from self or foreign origin to activate or deactivate cytotoxic CD8(+) T cells. Peptides are assembled with class I molecules by pathways that are either dependent or independent of transport by ABC proteins (TAP) and degradation in the immunoproteasome by its subunits LMP2 and LMP7. Those peptides that require TAP and LMP treatment appear to be subject to control and optimization by TAP for proper customizing and efficient presentation. Therefore, allelic variations in the coding sequences of TAP and LMP were suspected for a long time to be responsible for improper antigen processing, interruption of self-peptide presentation and reduced cell surface expression of MHC class I molecules resulting in the activation of autoreactive CD8(+) T cells. In this article we reviewed the controversial findings regarding the role of TAP and LMP genes in autoimmune diabetes and reevaluated data of eleven separate studies in a cross-study analysis by genotype and HLA haplotype matching. We could confirm previous results by showing that TAP2*651-A/F and TAP2*687-A/A are significantly associated with disease, independently of linkage disequilibrium (LD). LMP2-R/H surprisingly seems to be primarily disease-conferring although a weak association with DR4 serotypes can be observed. Our analysis also suggests that LMP7-B/B, TAP1-A/A and TAP2*687-A/B are the protective genotypes and that these associations are not secondary to LD with DRB1. Consequently, intracellular antigen processing associated with TAP- and proteasome-dependent pathways seems to be a critical element in T cell selection for the retention of a balanced immunity.

Is TAP2*0102 allele involved in insulin-dependent diabetes mellitus (type 1) protection?

In this study, we have investigated the frequencies of TAP1 and TAP2 alleles in a group of 226 persons, living in La Reunion Island, consisting of 70 patients with insulin-dependent diabetes mellitus (IDDM) and most of their first degree relatives (i.e., 156 parents and full sibling subjects) and previously HLA DQB1, DQA1, and DRB1 genotyped. The population of this island is constituted by a particular structure of highly crossbreeding people. Interestingly, the new TAP2*0104 allele, previously discovered by our team in Reunion Island, was found to be increased in the IDDM population and the calculated HRR was relatively high (HRR = 3.3). This result seems to be due to a positive linkage disequilibrium between TAP2*0104 allele and the highly diabetogenous DQB1* 0201-DQA1* 0501-DRB1 0301 haplotype (HRR = 9), which suggests that TAP2*0104 cannot be considered as an additional predispositional factor, but more as a genetic susceptibility marker of IDDM. In addition, we show that minor alleles (TAP2D, *0102, *0103, *0104) are associated with a restricted number of HLA DQ-DR haplotypes and each of them exhibits a preferential linkage with one particular haplotype. In contrast with other alleles, and despite a HRR value close to 1, we show that TAP2*0102 allele contributes significantly to a drastic reduction of the diabetogenic effect of DQB1*0201-DQA1*0301.1-DRB*0701 haplotype. Indeed, this haplotype, which is usually preferentially transmitted to affected children, is dominantly transmitted to healthy children when it is associated with TAP2*0102. Therefore, this allele seems to contribute to genetic protection to IDDM.

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.

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 the TAP1 and TAP2 genes in human alveolar echinococcosis

We postulated that TAP genes may influence the susceptibility of some individuals to Echinococcus multilocularis infection. Six coding region variants (codons 333 and 637 in TAP1, and 379, 565, 651 and 665 in TAP2) were typed in 94 patients and 100 controls. Thr/Thr homozygosity at TAP2/665 was more prevalent in patients than in controls [64% vs. 45%, respectively; odds ratio (OR) = 2.1 (95% confidence interval (CI) 1.1; 2.7)] and Thr/Ala heterozygozity was less prevalent (32% vs. 50%, respectively) (P = 0.014). Of the 38 patients with progressive lesions, 76% were Thr/Thr, as compared with 55% of patients without progressive lesions and 45% of controls (P = 0.058 and 0.02, respectively), independent of HLA status. To determine whether this association is functionally relevant, functional analyses and/or confirmation in distinct populations of patients with alveolar echinococcosis would be required.

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.

TAP1 and TAP2 gene polymorphism in rheumatoid arthritis in a population in eastern France

The 'transporter associated with antigen processing' (TAP) gene products are involved in the processing of endogenous peptides that bind to class I molecules. Polymorphism within these genes could alter the level of the immune response, a phenomenon relevant to the development of autoimmune diseases. In this study, we examined the polymorphism of TAP1 and TAP2 genes in patients with rheumatoid arthritis (RA). TAP1 and TAP2 typing was performed for 138 Caucasian RA patients and 100 healthy controls, all originating from eastern France. TAP1 polymorphic residues at positions 333 and 637 and amino acid variants 379, 565, 651 and 665 in the TAP2 gene were found using amplification refractory mutation system-polymerase chain reaction (ARMS-PCR). This method enabled us to determine four TAP1 alleles (TAP1A to TAP1D) and eight TAP2 alleles (TAP2A to TAP2H). All patients and controls had been HLA-DRB1* genotyped. The polymorphic residues TAP1333 and TAP1637 did not show any difference in their distribution between patients and controls. Similar findings were obtained for TAP2379 and TAP2665. However, we found an increased frequency of Thr homozygosity and heterozygosity at position 565 in the TAP2 gene in RA patients (RA vs. controls: 25.3 vs. 14%; P = 0.032; OR = 2.09; CI = 1.01-4.38). Similarly, the prevalence of subjects who were homozygote and heterozygote for Cys651 was increased in the RA group (RA vs. controls: 36.8 vs. 11%; P = 0.02). The dimorphic site TAP2565 defines TAP2D and TAP2E alleles, while the site at position 651 characterizes TAP2F. Thus, we found that TAP2D and TAP2E alleles were more prevalent in RA, but not significantly so (RA vs. controls: TAP2D: 10 vs. 3.6%; P = 0.24; TAP2E: 3.6 vs. 0%; P = 0.19). Similarly, the frequency of TAP2F was higher in RA patients (24.5%) than in controls (11.3%), but this was not significant after correction (P = 0.029; Pcorr = 0.17). Finally, we found no linkage disequilibrium between DRB1* RA-associated alleles and amino acid substitution Thr565 or TAP2D and TAP2E alleles, whereas Cys651 (and TAP2F) was not independent of DRB1*04, a strongly RA-associated allele. Finally, Thr at position 565 in the TAP2 gene was associated with manifestations of disease severity in only a few patients. Examination of TAP1 and TAP2 gene polymorphisms in RA patients revealed an association between a particular amino acid residue, namely Thr565 in the TAP2 gene, and RA. This association was found to be weak and did not seem to be a predictor for the severity of the disease.

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.

Distribution of HLA-A, B alleles and polymorphisms of TAP and LMP genes in Korean patients with atopic dermatitis

BACKGROUND

Atopic dermatitis has been seen to result from multifactorial inheritance, with interaction between genetic and environmental factors. The genetic association may differ according to the ethnic backgrounds.

OBJECTIVE

The purpose of this study was to investigate the genetic factors in Korean atopic dermatitis patients by studying the human leucocyte antigen (HLA) class I association and polymorphisms of transporters associated with antigen presentation (TAP) and low-molecular-weight polypeptide (LMP) genes.

METHODS

HLA-A and B genotyping was performed in 53 atopic dermatitis patients and 184 healthy controls using the standard microlymphocytotoxicity technique. TAP1, TAP2, LMP2, and LMP7 gene polymorphisms were anaylzed using the polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP), PCR-amplification refractory mutation system (ARMS), and PCR-restriction fragment length polymorphism (RFLP).

RESULTS

Allele frequency of HLA-A24 was significantly increased in patients with atopic dermatitis compared to controls (P < 0.05). HLA-B alleles showed no differences in distribution between patients and controls. Genotype, phenotype, and allele frequencies of TAP1 gene also revealed no differences in distribution between patients and controls. Analysis of TAP2 gene polymorphisms showed increased frequencies of the TAP2*C allele and TAP2*A/TAP2*C genotype in atopic dermatitis patients compared to controls (P < 0.05). Distribution of LMP2 and LMP7 gene polymorphisms was similar for patients and controls.

CONCLUSION

This study demonstrates an association of atopic dermatitis with HLA-A24 and TAP2*C alleles in Korean patients. Discrepancy with the previous reports might be related to different patient characteristics and ethnic variations.

HLA haplotype analysis in Finnish patients with rheumatoid arthritis

OBJECTIVE

To further characterize the HLA gene products that play an important role in the pathogenesis of rheumatoid arthritis (RA).

METHODS

One hundred thirty-four haplotypes from 67 Finnish RA patients and 77 control haplotypes were analyzed for HLA-DRB1 loci, associated alleles of the HLA-DQB1 locus, alleles of the type 2 transporter-associated antigen processing (TAP2) genes, and HLA-B27. In addition, a panel of microsatellite markers within the HLA class I and class III regions was studied.

RESULTS

The frequency of HLA-DRB1*04 in the haplotypes of RA patients was found to be 34% (45 of 134) compared with 14% (10 of 72) in control haplotypes (P = 0.004). The frequency of HLA-DRB1*13 was decreased in RA haplotypes (4%, or 5 of 134) in contrast to control haplotypes (24%, or 17 of 72) (P = 0.000031). The decrease in DRB1*13 was not secondary to the increase in DRB1*04, since it was also found among DRB1*04-negative haplotypes (P < 0.001). The DRB1*13-associated DQB1*0604 allele was similarly decreased in RA haplotypes (P = 0.025). The TAP2I allele of I/J dimorphism was increased in RA patients (85%, or 114 of 134) as compared with controls (69%, or 49 of 71) (P = 0.011). Of the tumor necrosis factor (TNF) microsatellite alleles, TNFa6 and TNFb5 were found to be increased in RA haplotypes (for a6 27% versus 5% in controls [P = 0.00043], and for b5 43% versus 26% in controls [P = 0.037]).

CONCLUSION

Both protection-associated and susceptibility-associated alleles can be found among HLA class II genes, and the results suggest that loci outside DR/DQ may contribute to the pathogenesis of RA.

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.

TAP2 alleles in inflammatory arthritis

Sixty patients with reactive arthritis (ReA) and 40 with rheumatoid arthritis (RA), were typed for H LA-B27 and class II antigens DR and DQ, and studied for TAP2 gene polymorphism in comparison with 60 healthy controls. TAP2 polymorphisms at positions 379, 565, 665, and 687 were analyzed using amplification refractory system-based PCR and polymorphisms at positions 386 and 651 using oligonucleotide hybridization. The frequency of the TAP2A/A genotype was 30%(12/40) in RA, in contrast to 13% (8/60) in the controls. This genotype was further associated with DRB1*04 positive RA (10/24, 42%, P=0.01), as well as the TAP2A allele (31/48, 65%, P =0.012). Thr/Thr dimorphism at TAP2 position 665 (24/40, 60%, P=0.024) and Stop/Stop dimorphism at TAP2 position 687 (24/40, 60%, P=0.024) were found to be increased in RA patients as compared to controls. When TAP2I/J polymorphism was studied, TAP2J positivity was found associated with the HLA-B27DR4-DQB1*0301-haplotype in ReA patients. 9/12 of these were positive as compared to 20/60 in random controls (P=0.010). Polymorphisms of the TAP2 gene were found to be associated with subgroups of RA and ReA patients with disease associated markers (e.g. TAP2A in DRB1*04 positive RA, or TAP2J in HLA-B27-DRB1*04-DQB1*0301 positive ReA). These may thus serve as additional markers of specific haplotypes associated with susceptibility to inflammatory arthritis.

Evaluation of TAP1 polymorphisms with insulin dependent diabetes mellitus in Finnish diabetic patients. The Childhood Diabetes in Finland (DiMe) Study Group

Insulin dependent diabetes mellitus (IDDM) is an autoimmune disease with a strong association between disease and the HLA class II region. Because abnormal antigen processing, in part characterized by altered class I processing, has been identified in patients with IDDM, the TAP (transporter associated with antigen processing) genes located in the HLA class II region make attractive candidate genes for IDDM. Five coding region variants of TAP1 were typed in a cohort of well characterized Finnish patients with diabetes (n = 119) and compared to racially marched control subjects (n = 92). We found that although no single TAP1 polymorphism was associated with IDDM, a genotypic combination of Ile/Val at codon 333 with Asp/Asp at codon 637 was found more frequently in subjects with IDDM (9.4%) compared to controls (1.2%; p = 0.025). This could not be accounted for by an association with any particular haplotype defined by class I or class II serology.

Human TAP1 polymorphisms detected by denaturing gradient gel electrophoresis

Presentation of endogenous peptides by major histocompatibility complex class I (MHC) molecules is controlled, in part, by the Tap1 and Tap2 genes in the MHC class II region that encode a heterodimeric peptide transporter. Polymorphisms of human Tap1 in normal individuals have now been investigated systematically by denaturing gradient gel electrophoresis (DGGE) analysis of fragments of genomic DNA generated by the polymerase chain reaction. Polymorphisms identified by distinctive DGGE band patterns were confirmed by DNA sequencing. In addition to four previously described polymorphisms in the open reading frame, DGGE detected three new polymorphisms: a G-->T substitution in the promoter region, a 10-bp insert in intron 9, and a G-->T substitution 80-bp downstream of the translation termination codon.

Analysis of allelic variation of the TAP2 gene in sarcoidosis

Sarcoidosis is a systemic granulomatous disease and the DRB1 gene of the DR subregion has been implicated for determining the genetic susceptibility to the disease. We evaluated the allelic variation of the TAP2 gene using the PCR-RFLP method as well as the mismatched PCR-RFLP method in 82 Japanese patients with sarcoidosis and 92 healthy controls. A new allele, TAP2*0103 and a new polymorphic variation at codon 577 in addition to TAP2*0101, TAP2*0102 and TAP2*0201 have been recognized in the Japanese subjects. No significant differences were observed in the frequencies of any TAP2 alleles or dimorphism at codon 577 between the patients and healthy controls. Polymorphic variation of the TAP2 gene does not confer the susceptibility to sarcoidosis.

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.

Identification of new TAP2 alleles in gorilla: evolution of the locus within hominoids

Transporters associated with antigen processing molecules (TAP1 and TAP2) mediate the transfer of cytosolic peptides into the lumen of the endoplasmic reticulum for association with newly synthesized class I molecules of the major histocompatibility complex. Previous molecular and functional analyses of rat and human TAP2 homologues indicated major differences in gene diversification patterns and selectivity of peptides transported. Therefore, in this study, we analyzed the alleles of the gorilla TAP2 locus to determine whether the pattern of diversification resembled that in either of those two species. Sequence analysis of the TAP2 cDNAs from gorilla Epstein-Barr virus-transformed B-cell lines revealed four alleles with a genetic distance of less than 1%. The nucleotide substitutions distinguishing the alleles are confined to the 3' half of the coding region and occur individually or within two small clusters of variability. Diversification of the locus appears to have resulted from point substitutions and recombinational events. Evolutionary-rate estimates for the TAP2 gene in gorilla and human closely approximate those observed for other hominoid genes. The amino acid polymorphisms within the gorilla molecules are distinct from those in the human homologues. The absence of ancestral polymorphisms suggests that gorilla and human TAP2 genes have not evolved in a trans-species fashion but rather have diversified since the divergence of the lineages.