Association of the TAP2*Bky2 allele with presence of SS-A/Ro and other autoantibodies in Japanese patients with systemic lupus erythematosus

Variation in the ATP-binding cassette transporter 2 gene is a separate risk factor for systemic lupus erythematosus within the MHC

The ATP-binding cassette transporter (TAP) proteins are functionally relevant candidates for predisposition to systemic lupus erythematosus (SLE) by virtue of their role in autoantigen presentation and location in the major histocompatibility complex (MHC). We tested if variation in the TAP genes (TAP1 and TAP2) is associated with SLE. We genotyped tag single nucleotide polymorphisms (SNPs) and performed family-based association analysis on 390 Caucasian pedigrees. We found significant evidence of association between TAP2 and SLE (rs241453, P=1.33 x 10(-6)). Conditional logistic regression analysis suggests that this TAP2 effect is separate from the HLA-DRB1 alleles. Our analyses show that both rs241453 (P=1.6 x 10(-4)) and HLA-DRB1*03xx (P=2.3 x 10(-4)) have significant autonomous effects not due to linkage disequilibrium. Moreover, these loci exhibit a significant statistical interaction (P<1.0 x 10(-6)), demonstrated by an increase in the odds ratio for the TAP2 association from OR=2.00 (95% confidence interval (CI)=1.17-3.42) in HLA-DRB1*03xx-negative subjects to OR=4.29 (CI=1.88-9.76) in the subjects with at least one HLA-DRB1*03xx allele group. We report the largest association study of the TAP genes with SLE to date, and the first to test for its separate effect and interaction with the HLA alleles consistently associated with SLE.

TAP1 and TAP2 Gene Polymorphisms and HLA-TAP Haplotypes in Koreans Based on 90 Families

We have investigated the polymorphism of TAP genes and the distribution of human leukocyte antigen (HLA)-TAP haplotypes in 90 Korean families (180 parents and 233 children), previously typed for HLA class II alleles. TAP1 (codons 333 and 637) and TAP2 (codons 379, 565, 577, 651, 665, and 687) typings were carried out by use of polymerase chain reaction-restriction fragment length polymorphism method. For TAP1, four alleles (gene frequency: A 81.9%, B 15.0%, C 2.5%, D 0.5%) and for TAP2, nine alleles (A1 31.7%, A2 14.2%, B 32.5%, Bky2 6.1%, C 6.9%, D 2.5%, E 3.9%, G 0.8%, and H 1.4%) were detected. Sixteen different TAP1-TAP2 haplotypes were observed with frequencies > 0.5%, and we found that significant linkage disequilibrium was present between TAP1 and TAP2 loci (p < 0.001). When HLA-DRB1-DQB1 haplotypes were extended to TAP1 and TAP2 loci, much diversification of haplotypes was observed: 26 different DRB1-DQB1 haplotypes (frequencies > 0.8%) formed 90 different extended haplotypes. Eight recombinant haplotypes between DQB1 and DPB1 loci were observed, and most (seven of eight) of the recombinations occurred between TAP2 and DPB1 loci. These results add more evidence to the view that recombination hot spot is present within and around TAP gene region.

Genetics of systemic lupus erythematosus: how far have we come?

There are two primary mechanisms for studying the genetic forces at work in systemic lupus erythematosus (SLE). Several groups have collected large numbers of pedigrees in which multiple family members have SLE for use in linkage studies. These linkage studies serve to isolate areas of the genome in which susceptibility genes lie. Other groups have taken a more direct approach of investigating genes that might contribute to disease pathogenesis in sets of lupus subjects and matched controls. These association studies are accumulating in greater numbers as the technology to determine the genotype at a given locus becomes more accessible. This article discusses the results of both types of studies.

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.

TAP genes and immunity

The transporter associated with antigen processing (TAP) is a member of the ATP-binding cassette transporter family that specializes in delivering cytosolic peptides to class I molecules in the endoplasmic reticulum. The TAP is a major target of genetic alteration in tumours and disruption by viral inhibitors. In some species, TAP genes have co-evolved with MHC class I molecules to deliver peptides that are customised for particular alleles. In humans, MHC class I polymorphism determines the level of tapasin-mediated association with TAP and subsequent peptide optimisation within the peptide-loading complex (PLC). MHC class I molecules that still load peptides without complexing to the TAP might be more resistant to viral interference of the PLC and less sensitive to competition for TAP by other class I allotypes.