Genetic polymorphisms of the major histocompatibility complex-encoded antigen-processing genes TAP and LMP in sarcoidosis

[Sarcoidosis and genetics]

Familial features of sarcoidosis and observations in monozygotic twins affected by the condition suggest the presence of a genetic predisposition. Various genetic associations have been described with genes coding for proteins involved in immune regulation in particular at the level of interaction between T-lymphocyte and antigen presenting cell. We review the various genetic targets described with techniques ranging from classic human lymphocyte antigen genotype to genome wide linkage scans. The 6p21 region has been highlighted, which includes relevant genes such as MHC class II, BTNL2 and TNFα. These studies show that the genetics of sarcoidosis are complex, that patient sub-groups exist, which may explain some of the heterogeneity in the results of genetic studies and that the interactions between genetic and environmental factors remains to be elucidated.

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.

Genetics of sarcoidosis

The predisposition to sarcoidosis is genetically determined, and genetics appears also to account for the variability in clinical phenotype and behaviour. Many genetic loci have been investigated to date, mainly in case-control association studies. However, only a small number of human leukocyte antigen (HLA) alleles have been consistently associated with sarcoidosis susceptibility/phenotype. In this regard, the association between Löfgren's syndrome and the extended HLA-DRB1*0301/DQB1*0201 haplotype is probably the most extensively reproduced. Several, generally less convincing, associations have been also reported. Of these, the chemokine receptor and butyrophilin-like 2 (BTNL2) associations are most promising. However, two major limitations of genetic studies are that the understanding of the biological relevance of gene variations in the genome is still incomplete and that the reported associations need to be verified in populations of different ethnicities. Despite a number of intriguing hypotheses, what causes sarcoidosis remains obscure. Genetic studies and, importantly, functional analysis of candidate genes will provide insight into pathogenesis and disease risk. However, if, as many believe, sarcoidosis is a heterogeneous collection of disorders, a critical step will be to carefully refine the clinical phenotype, as genetic studies of complex diseases are more rewording if a very specific disease subset is addressed.

Role of genetic polymorphisms in ACE and TNF-alpha gene in sarcoidosis: a meta-analysis

A great number of association studies have been performed to identify the genes involved in the etiology and prognosis of sarcoidosis. We performed a systematic review of case-control studies through the PubMed database and evaluated them for a possible inclusion into a meta-analysis in order to assess whether the reported genetic polymorphisms are the risk factors of sarcoidosis. Case-control studies with clear diagnostic criteria and interventions were included. Only investigations of a single polymorphism/gene involvement in sarcoidosis reported more than five times were selected. Aggregating data from 12 studies on ID/ACE polymorphisms, the odds ratio (OR) for sarcoidosis, if the polymorphism was considered under the dominant genetic model, was not significantly increased: 1.19 (95% CI 0.98-1.43); OR under the recessive model was 1.20 (95% CI 0.98-1.46). In seven case-control studies on -308/TNF-alpha polymorphism, the OR for sarcoidosis if the polymorphism considered under the dominant genetic model was significantly increased at 1.47 (95% CI 1.03-2.08); the OR under the recessive model was 1.39 (95% CI 0.67-2.90). In conclusion, the results showed that the TNF-alpha genotype could be a significant risk factor for sarcoidosis, whereas the risk of sarcoidosis due to the ACE genotype was not substantially elevated.

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.

Two major histocompatibility complex haplotypes influence susceptibility to sporadic inclusion body myositis: critical evaluation of an association with HLA-DR3

Previous studies of sporadic inclusion body myositis (sIBM) have shown a strong association with HLA-DR3 and other components of the 8.1 ancestral haplotype (AH) (HLA-A1, B8, DR3), where the susceptibility locus has been mapped to the central major histocompatibility complex (MHC) region between HLA-DR and C4. Here, the association with HLA-DR3 and other genes in the central MHC and class II region was further investigated in a group of 42 sIBM patients and in an ethnically similar control group (n = 214), using single-nucleotide polymorphisms and microsatellite screening. HLA-DR3 (marking DRB1*0301 in Caucasians) was associated with sIBM (Fisher's test). However, among HLA-DR3-positive patients and controls, carriage of HLA-DR3 without microsatellite and single-nucleotide polymorphism alleles of the 8.1AH (HLA-A1, B8, DRB3*0101, DRB1*0301, DQB1*0201) was marginally less common in patients. Patients showed no increase in carriage of the 18.2AH (HLA-A30, B18, DRB3*0202, DRB1*0301, DQB1*0201) or HLA-DR3 without the central MHC of the 8.1AH, further arguing against HLA-DRB1 as the direct cause of susceptibility. Genes between HLA-DRB1 and HOX12 require further investigation. BTL-II lies in this region and is expressed in muscle. Carriage of allele 2 (exon 6) was more common in patients. BTL-II(E6)*2 is characteristic of the 35.2AH (HLA-A3, B35, DRB1*01) in Caucasians and HLA-DR1, BTL-II(E6)*2, HOX12*2, RAGE*2 was carried by several patients. The 8.1AH and 35.2AH may confer susceptibility to sIBM independently or share a critical allele.

Sarcoidosis

There have been several new insights into the cause and treatment of sarcoidosis. Studies of genetic variation have shown that specific genetic polymorphisms are associated with increased risk of disease or affect disease presentation. These polymorphisms include variation of MHC and cytokines such as tumour necrosis factor (TNF). Not all investigators have come to the same conclusion, suggesting an interaction of various factors, including the patient's ethnic origin. Treatment of sarcoidosis varies considerably. Patients with symptomatic disease for more than 2-5 years have been of particular interest. Corticosteroids remain the standard of care in such cases, but immunosuppressive drugs have proved steroid-sparing in many patients. New agents, including pentoxifylline, thalidomide, and infliximab have proved useful in selected cases. The effectiveness of these agents seems to lie in their ability to block TNF, especially in the treatment of chronic disease.

A single nucleotide polymorphism of the low molecular mass polypeptide 7 gene influences the interferon response in patients with chronic hepatitis C

Transporter associated with antigen processing (TAP) and low molecular mass polypeptides (LMP) play crucial roles in the human leukocyte antigen (HLA) class I-restricted antigen presenting systems. This study was performed to elucidate whether these antigen-presenting gene polymorphisms could influence the response to interferon (IFN) treatment in patients with chronic hepatitis C. Polymorphisms of TAP and LMP genes in 175 hepatitis C virus (HCV) patients were determined by polymerase chain reaction-restriction fragment length polymorphism. The frequencies of these genes were compared between sustained-responders (n=49) and nonresponders (n=126), classified by biochemical and virological responses to IFN. The distributions of TAP1*, TAP2*, and LMP2 genes between sustained-responders and nonresponders did not differ. However, LMP7-K gene frequency in sustained-responders was higher than that in nonresponders [odds ratio 2.3 (95% confidence interval 1.1-4.6); 16%vs 7.9%]. Multivariate analysis revealed that LMP7-K and HCV-RNA quantity were independent factors influencing the outcome of IFN therapy [4.5 (1.4-14); P=0.011, 0.40 (0.24-0.65); P=0.0003, respectively]. Furthermore, among patients with a low viral load (< or = 2.0 Meq/mL), the LMP7-K positive patients had an even higher ratio of sustained response compared to those without LMP7-K [5.9 (1.6-22); 82%vs 44%; P=0.0062]. These findings suggest that a single nucleotide polymorphism of LMP7 gene is one of the important host factors which independently influence the response to IFN in patients with chronic hepatitis C.

Genotyping in the MHC locus: potential for defining predictive markers in sarcoidosis

In sarcoidosis, host genetic factors are discussed as contributing to disease susceptibility and course. Since tumor necrosis factor (TNF)-alpha is a central mediator of granuloma formation and since elevated TNF-alpha levels are found during active phases of sarcoidosis, genetic polymorphisms correlating with influences on TNF-alpha levels are of special interest. The complete sequencing of the MHC region and the increase in the number of identified gene polymorphisms in this locus associated with TNF-alpha production offer the opportunity of detecting new genes associated with sarcoidosis and perhaps of defining disease-associated haplotypes that bear the potential of serving as predictive markers for this disease.

Surfactant gene polymorphisms and interstitial lung diseases

Pulmonary surfactant is a complex mixture of phospholipids and proteins, which is present in the alveolar lining fluid and is essential for normal lung function. Alterations in surfactant composition have been reported in several interstitial lung diseases (ILDs). Furthermore, a mutation in the surfactant protein C gene that results in complete absence of the protein has been shown to be associated with familial ILD. The role of surfactant in lung disease is therefore drawing increasing attention following the elucidation of the genetic basis underlying its surface expression and the proof of surfactant abnormalities in ILD.

TAPI polymorphisms in several human ethnic groups: characteristics, evolution, and genotyping strategies

Genetic variations in the locus encoding the transporter associated with antigen processing, subunit 1 (TAP1), were systematically studied using samples from Caucasians, Africans, Brazilians, and compared with data from chimpanzees. PCR-amplified genomic sequences corresponding to the 11 exons were analyzed by single-strand conformation polymorphism (SSCP) and sequencing. Six nonsynonymous and 2 synonymous single nucleotide polymorphisms (SNPs) were found to be common in one ethnic group or another, and they involved codons 254 (Gly-GGC/Gly-GGT) in exon 3, 333 (Ile-ATC/Val-GTC) in exon 4, 370 (Ala-GCT/Val-GTT) in exon 5, 458 (Val-GTG/Leu-TTG) in exon 6, 518 (Val-GTC/Ile-ATC) in exon 7, 637 (Asp-GAC/Gly-GGC), 648 (Arg-CGA/Gln-CAA) and 661 (Pro-CCG/Pro-CCA) in exon 10. At each SNP site the sequence listed first was predominant in all ethnic groups. Several SNPs segregated on the same chromosome regardless of populations and species. Together, the SNPs produced 5 major human TAP1 alleles, 4 of which matched the officially recognized alleles *0101, *02011, *0301, and *0401; the 5th allele differed from each of those by at least 4 SNPs. Overall, TAP1*0101 was the predominant allele in all ethnic groups, with frequencies ranging from 0.667 in Zambians to 0.808 in US Caucasians. The TAP1*0401 frequency showed the greatest difference between Africans (0.221-0.254) and Caucasians (0.033), with Brazilians (0.058) fitting in the middle. Consistent with earlier work based on Caucasians and gorillas, *0101 appeared to be the newest human TAP1 allele, suggesting a dramatic spread of *0101 into all human populations examined. Characterization of TAP1 polymorphisms allowed the design of a PCR-based genotyping scheme that targeted 7 SNP sites and required 2 separate genotyping techniques.

Significance of transporter associated with antigen processing gene polymorphism in living related renal transplantation

The HLA class I and class II mediated antigen presentation plays a major role in the initiation of immune response and the development of acute rejection after transplantation. The purpose of this study was to examine whether MHC-encoded antigen processing (TAP1, TAP2, LMP2, DMA and DMB) gene polymorphisms were associated with the incidence and the severity of acute rejection after renal transplantation. We studied a selected population of 112 pairs of donors and recipients who underwent living-related renal transplantation. They were divided into 3 groups: rejection-free (Group A, n = 51), steroid-sensitive rejection (Group B, n = 31) and steroid-resistant rejection (Group C, n = 30). The frequency of TAP2*0103 (41.2%) was significantly higher in the donors of Group A than that of Group B (12.9%, p = 0.0070, pc = 0.0280) or Group C (16. 7%, p = 0.0225, pc = 0.0900). No significant difference was observed in the allelic frequencies of the TAP1, LMP2, DMA, and DMB genes in the donors or recipients among Groups A, B, and C. This result supported the idea that the TAP2 gene polymorphism might be functionally related to antigen presentation. It also suggested that donor's antigen presenting cells with the TAP2*0103 allele would have the attenuated efficacy in the presentation of allospecific antigens to recipient's T cells.

HLA-DQB1*0601 is primarily associated with the susceptibility to cardiac sarcoidosis

Cardiac sarcoidosis occurs in 1-5% of sarcoidosis patients. We previously reported a significant increase of the uncommon TNFA (tumor necrosis factor alpha) allele, TNFA2 with cardiac sarcoidosis in Japanese. In order to precisely localize the susceptible locus for cardiac sarcoidosis within the HLA region, genetic polymorphisms of classical HLA genes, non-classical HLA class II genes such as HLA-DMA and -DMB genes and several genes involved in the class I-mediated antigen presentation pathway (TAP1, TAP2, LMP2 and LMP7) were investigated. Further, association analyses using four polymorphic microsatellite markers located around the TAP1 and TNFA genes were also carried out. As a result, HLA-DQB1*0601 was found to be the most significantly associated allele, being more significantly increased than TNFA2. No significant increase of the DR52-associated DRB1 alleles (DRB1*03, 05, 06 and 08), which was suggested to be primarily associated with lung sarcoidosis, was observed in cardiac sarcoidosis. A primary role of DQB1*0601 in determination of the susceptibility to cardiac sarcoidosis was supported by association analysis using four polymorphic microsatellite markers, in which only the TAP1 microsatellite locus, the nearest marker to the DQB1 gene among the microsatellites tested, displayed a significant positive association with cardiac sarcoidosis. On the other hand, the HLA-DQB1*0501-DQA1*0101-DRB1*0101-B7 haplotype showed a negative association with the disease, as similarly observed in lung sarcoidosis. Thus, molecular mechanism for controlling the development of the disease related to HLA molecules are different between cardiac and lung sarcoidosis, whereas those for conferring a resistant trait may be similar to each other.

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.

Analysis of MHC encoded antigen-processing genes TAP1 and TAP2 polymorphisms in sarcoidosis

Sarcoidosis is a chronic granulomatous disease of unknown etiology. Several studies have suggested involvement of human leukocyte antigen (HLA) genes in sarcoidosis susceptibility. HLA associations described have not been consistent, possibly because of additional susceptibility genes adjacent to or within the major histocompatibility complex (MHC) such as genes for the transporter associated with antigen processing (TAP). The aim of this study was to analyze TAP gene polymorphisms in patients with sarcoidosis using the amplificatory refraction mutation system (ARMS) PCR. To determine whether any association between TAP gene variation and sarcoidosis was ethnic-independent we examined two European populations: 117 unrelated UK Caucasoid patients with sarcoidosis and 290 healthy UK control subjects, and 87 unrelated Polish Slavonic patients with sarcoidosis and 158 healthy Polish control subjects. We detected significant differences in TAP2 between the UK control and patient groups, and in TAP2 between the Polish control and patient groups. Comparing the UK and Polish control groups, we observed a difference in TAP1. Examination of HLA-DPB1 in our UK population showed no associations with disease or between variants at the TAP gene loci and HLA-DPB1 variants. These results suggest associations at the TAP loci occur independently of HLA-DPB1 associations, that TAP associations seen may be involved in determining sarcoidosis susceptibility, and that such susceptibilities differ between UK and Polish populations. This first study of TAP genes in UK and Polish sarcoid populations has demonstrated the importance of using multiple defined ethnic populations in defining the role genetic factors play in sarcoidosis susceptibility and the importance of candidate gene studies.

Characterization of LMP polymorphism in homozygous typing cells and a random population

Within the class II region of the MHC are several genes whose products are involved in processing antigen for HLA class I presentation. Two such genes, LMP2 and LMP7, encode products that are incorporated into a multicatalytic proteinase complex which serves as the major pathway for protein degradation for class I peptide presentation. Polymorphic residues have been identified in both LMP2 and LMP7. In this report, we describe an ARMS-PCR method to distinguish LMP7 alleles. We applied this method to characterize these alleles in addition to LMP2 alleles in 50 homozygous typing cells (HTC) as well as in a panel of 110 random individuals. Of the four possible combinations of LMP2 and LMP7, we observed three in the HTC population, while all four were observed in the random population. The frequencies at which allele combinations were observed were similar to that predicted by individual allele frequencies. We also analyzed the possibility of linkage disequilibrium of LMP2 and LMP7 alleles with TAP1, TAP2, and specific HLA class I alleles in both populations. From this data, there seems to be no apparent linkage disequilibrium and no indication that particular combinations of LMP2 and LMP7 have been maintained.

Extended HLA haplotypes in Japanese homozygous typing cells

We have defined extended HLA haplotypes including the HLA class II genes, the non-HLA genes such as TAP1, TAP2 and LMP2, and the (CTG)n microsatellite repeats within the NOTCH4 gene between DRA and 21OH in 33 Japanese HLA homozygous typing cells (HTC). These conserved haplotypes characterized by unique linkage might be maintained as a result of functional co-operation among them in the antigen presentation pathway. These HTCs can be served as an original and ethnic-specific standard panel, providing useful genetic markers in haplotypic diversity, disease association, and anthropology studies.

Transporter associated with antigen-processing (TAP) genes and susceptibility to tuberculoid leprosy and pulmonary tuberculosis

We have studied TAP polymorphism in a panel of 40 healthy individuals, 57 patients with pulmonary tuberculosis (PTB) and 50 with tuberculoid (TT) leprosy from North India. Only TAP2-A/F occurred with a significantly increased frequency in PTB patients as compared to controls (82.5% vs. 52.5%, P < 0.002, Pc < 0.01) giving a high relative risk of 4.3. On the other hand, TAP2-B was significantly increased in TT leprosy as compared to controls (76% vs. 47.5%, Pc < 0.003, RR 3.5) particularly in patients positive for HLA-DR15 than controls carrying DR15 (77.5% vs. 50%, P < 0.03, RR = 3.4). Further, TAP2-B allele was positively associated with DR15 negative PTB patients as compared to the DR15 positive group (43.8% vs. 17.1%, P < 0.04, RR = 0.3). This study along with our earlier studies on HLA association in mycobacterial diseases suggests that in addition to HLA-DR15 alleles in the TAP2 region influence susceptibility to PTB and TT leprosy.

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.