HLA-D region genomic polymorphism associated with Takayasu's arteritis

The genetics of Takayasu arteritis

Takayasu arteritis (TAK) is a rare systemic vasculitis that is characterized by granulomatous inflammation of the aorta and its major branches. The cellular and biochemical processes involved in the pathogenesis of TAK are beginning to be elucidated, and implicate both cell and antibody-mediated autoimmune mechanisms. In addition, the underlying etiology to TAK may be explained, at least in part, by a complex genetic contribution. The most well-recognized genetic susceptibility locus for the disease is the classical HLA allele, HLA-B*52, which has been confirmed in several ethnicities. The genetic susceptibility with HLA-B*52, as well as additional classical alleles and loci, implicate both HLA class I and class II involvement in TAK. Furthermore, genetic associations with genes encoding immune response regulators, pro-inflammatory cytokines and mediators of humoral immunity may directly relate to disease mechanisms. Non-HLA susceptibility loci that have been recently established for TAK with a genome-wide level of significance include FCGR2A/FCGR3A, IL12B, IL6, RPS9/LILRB3, and a locus on chromosome 21 near PSMG1. In this review, we present the complex genetic predisposition to TAK and discuss how recent findings identified potential targets in the pathogenesis and treatment of the disease.

Revisited HLA and non-HLA genetics of Takayasu arteritis--where are we?

Takayasu arteritis (TAK) is an immune-mediated vasculitis affecting large arteries first reported in 1908 from Japan. Case reports of familial onset of TAK from Japan and other countries indicated genetic contribution to TAK onset beyond ethnicity. Genetic studies of TAK have been performed mainly addressing the human leukocyte antigen (HLA) locus. HLA genetic studies of TAK that have previously been reported are reviewed in this manuscript. HLA-B*52:01 is associated with TAK beyond population. Many of the associations other than HLA-B*52:01 can be explained by a haplotype with HLA-B*52:01. HLA-B*67:01 is a novel susceptibility HLA-B allele to TAK confirmed in the Japanese population. Further independent associations are suggested in the HLA locus. Involvement of the 171st and 67th amino acid residues with TAK onset has been indicated. The 67th amino acid may explain the difference in susceptibility effects to TAK and Behçet's disease between HLA-B*52:01 and *51:01. HLA-B*52:01 is associated not only with TAK susceptibility but also with clinical phenotypes. Recent genome-wide association studies of TAK revealed multiple non-HLA susceptibility genes. In particular, the IL12B region seems to have a central role in TAK onset and its progression. Whether TAK and giant cell arteritis (GCA), the other vasculitis affecting large arteries, are the same disease is an interesting question to address in spite of different clinical manifestations between the two diseases. GCA is associated with HLA-DR4, which is not associated with TAK. GCA is not associated with HLA-Bw52. These two diseases seem not to share non-HLA susceptibility loci based on the recent genetic studies.

Surgical management of Takayasu's arteritis

The results of surgical bypass and endarterectomy in Takayasu's arteritis (TA) were reported to be poor compared to usual atherosclerosis patients. However, if ischemic symptoms due to occlusive disease were severe, surgical procedures were inevitable. We report surgical experience of 5 patients with TA. Five women (ranged from 26 to 58 yr) were operated between June 1998 and May 2004. Three patients showed occlusion of main branches of aortic arch and had symptoms of cerebral ischemia. One patient showed near total occlusion in the midabdominal aorta and had symptoms of orthopnea and uncontrolled hypertension. One patient showed total occlusion of abdominal aorta at the level of aortic bifurcation and had a symptom of severe claudication on both legs. Bypasses from the ascending aorta to the carotid artery were performed in 3 cases. Bypass from the thoracic aorta to the left common iliac artery was performed in one case and endarterectomy of abdominal aorta in one case. The ischemic symptoms related with arterial occlusion were resolved after surgery. And the symptoms of cardiac failure disappeared. The symptomatic TA frequently required arterial reconstruction. The symptomatic improvement and excellent mid-term patency could be expected after arterial reconstruction and endarterectomy.

Angiographic findings and surgical treatments of coronary artery involvement in Takayasu arteritis

BACKGROUND

Takayasu arteritis is associated with a low incidence of coronary artery involvement, such as stenosis, obstruction, aneurysm, and coronary steal syndrome, but coronary ischemia can be fatal.

METHODS

Between 1972 and April 2001, 81 of 130 patients given a diagnosis of Takayasu arteritis underwent selective coronary angiography, and among them, 31 patients (4 male and 27 female patients; mean age, 41.1 +/- 13.2 years) had abnormal coronary angiographic findings and were recruited for this study.

RESULTS

Abnormal coronary findings consisted of 24 coronary artery stenoses of greater than 75%, 3 coronary artery-bronchial artery anastomoses, 3 aneurysmal coronary ectasias, and 1 combined coronary ectasia and anastomosis. Among 24 patients with coronary stenosis, the ostium was most frequently involved (87.5%). Twenty-three of 24 patients with coronary artery stenoses were treated surgically. The mean follow-up duration was 9.65 +/- 6.9 years, with a 100% follow-up rate. Four fistulas and 4 aneurysms in 7 patients were not treated surgically. Coronary steal phenomenon was always associated with occluded pulmonary arteries and pulmonary hypertension. Aneurysmal coronary ectasia was related to severe aortic hypertension with or without aortic regurgitation and atypical coarctation. There were 2 (8.7%) in-hospital deaths and 3 (13%) late deaths. The actuarial survival rate, including in-hospital deaths, was 86.5% +/- 7.3% at 5 years and 81.4% +/- 8.4% at 10 years.

CONCLUSION

The incidence of coronary abnormalities is relatively low in patients with Takayasu arteritis; however, surgical treatment is recommended for patients with coronary ostial stenoses because coronary ischemia can be one of the major causes of death.

Takayasu arteritis: insights into immunopathology

Takayasu arteritis is an acute and sometimes chronic form of vasculitis involving the aorta, its main branches and pulmonary arteries. Although its etiology is still unknown, immunopathologic analyses revealed that the infiltrating cells mainly consisted of gammadelta T-cells as well as alphabeta T-cells and NK cells. The infiltrating gammadelta T-cells, cytotoxic T-lymphocytes (CTLs), and natural killer (NK) cells directly injured the vascular cells by releasing a cytolytic factor, perforin. Expression of heat-shock protein (HSP)-65 as well as human leukocyte antigen (HLA) class I and II was enhanced in Takayasu arteritis lesions, supporting the pathogenic role of gammadelta T-cells and alphabeta T-cells. T-cell receptor (TCR) alphabeta gene usage by the infiltrating cells was restricted, strongly suggesting that a specific antigen was targeted. TCR gammadelta gene usage by the infiltrating cells was also restricted. Furthermore, it has been reported that a strong association with a specific haplotype of major histocompatibility complex (MHC) class I chain-related (MIC), MICA gene with Takayasu arteritis, suggesting that the HLA-linked gene susceptible to the disease is mapped near the MICA gene. This also supports a pathogenic role of gammadelta T-cells in Takayasu arteritis because gammadelta T-cells were shown to recognize MICA molecule, which can be stress-induced. These findings suggest that unknown stress, such as infection, may trigger the autoimmune process of inflammation involved in Takayasu arteritis.

Association of clinical manifestations with HLA-B alleles in Takayasu arteritis

HLA-DNA typing using PCR-SSOP and PCR-DCP methods was performed in 85 patients with Takayasu arteritis and 492 healthy controls who had been typed for HLA by serological method. Frequencies of HLA-B52 (B*5201) and B39 (B*3901 and B*3902) were significantly increased in the patients. Frequency of HLA-DRB1*1502 was also increased but it was suggested to be a reflection of its linkage disequilibrium with B52. Association of HLA-B52 and B39 with seven clinical manifestations--pulmonary infarction, ischemic heart disease, aortic regurgitation, systemic hypertension, renal artery stenosis, cerebrovascular disease, and visual disturbance--in 132 HLA-typed patients with Takayasu arteritis was studied. In HLA-B52 positive TA patients, aortic regurgitation (vs B52(-)-B39(+), OR=3.8, P<0.05, vs B52(-)-B39(-), OR=5.49, P<0.001), ischemic heart disease (vs B52(-)-B39(+), OR=12.05, P<0.05, vs B52(-)-B39(-), OR=2.85, P<0.05), and pulmonary infarction (vs B52(-)-B39(+), OR=5.74, P<0.03) were found to be significantly prevalent. On the other hand, in HLA-B39 positive TA patients, frequency of renal artery stenosis was significantly increased (vs B52(+)-B39(-), OR=12.14, P<0.001, vs B52(-)-B39(-), OR=5.21, P<0.03). These observations have suggested that HLA-B52 molecule and B39 molecule would contribute to different clinical manifestations by binding different antigenic peptides to cause inflammations. Thus HLA-B molecule may play an important role in pathogenesis or determining clinical manifestations of Takayasu arteritis.

Direct role of HLA-B5 in influencing susceptibility to Takayasu aortoarteritis

To investigate genetic factors involved in the pathogenesis of Takayasu arteritis (TA), North Indian patients belonging to the states of Punjab, Haryana, Uttar Pradesh and Delhi were examined for HLA-class I and class II antigens and the data compared with healthy controls from the same ethnic group. Additionally, DNA typing was performed using polymerase chain reaction/sequence specific oligonucleotide probe (PCR-SSOP) technique to evaluate the distribution of molecular alleles in the healthy Indian population as compared to orientals and Western caucasoids. The frequency of HLA-B5 was significantly increased in patients as compared to controls (chi 2 = 32.5, corrected P value, Pc = 3 x 10(-6), relative risk = 4.3). Serological splitting of B5 into B51 and B52 did not reveal an association with any of the two subtypes. Weak association was also noticed with DR8 in the patient group (chi 2 = 8.2, Pc = 0.05). Distribution of the molecular subtypes of various HLA-B and DR alleles indicated that although the Indian population is essentially caucasoid, it comprises of an admixture of both caucasoid as well as oriental alleles/haplotypes. The observations clearly suggest that (a) HLA-linked genes are involved in the development of Takayasu arteritis, and (b) rather than a subtype of B5, the whole molecule or its closely linked gene(s) influence susceptibility to TA.

Perforin-secreting killer cell infiltration and expression of a 65-kD heat-shock protein in aortic tissue of patients with Takayasu's arteritis

Cell-mediated autoimmunity has been strongly implicated in the pathogenesis of vascular cell injury in Takayasu's arteritis. To clarify the immunological mechanisms involved, we examined the expression of a cytolytic factor, perforin in infiltrating cells of aortic tissue samples from seven patients with Takayasu's arteritis. We also examined the expression of a 65-kD heat-shock protein (HSP-65), human leukocyte antigen classes I and II, and intercellular adhesion molecule-1 in the aortic tissue. Immunohistochemical studies showed that the infiltrating cells mainly consisted of gamma delta T lymphocytes, natural killer cells, macrophages, cytotoxic T lymphocytes and T helper cells, and that perforin was expressed in gamma delta T lymphocytes, natural killer cells, and cytotoxic T lymphocytes. In situ hybridization analysis also revealed expression of perforin mRNA in the infiltrating cells. Immunoelectron microscopic studies demonstrated that the infiltrating cells released massive amounts of perforin directly onto the surface of arterial vascular cells. We also found that expression of HSP-65, human leukocyte antigen classes I and II, and intercellular adhesion molecule-1 was strongly induced in the aortic tissue and might facilitate the recognition, adhesion and cytotoxicity of the infiltrating killer lymphocytes. These findings provide the first direct evidence that the infiltrating cells in the aortic tissue mainly consist of killer cells, and strongly suggest that these killer cells, especially gamma delta T lymphocytes, may recognize HSP-65 and play a critical role in the vascular cell injury of Takayasu's arteritis by releasing perforin.

DNA typing of HLA-B gene in Takayasu's arteritis

Sixty-four patients with Takayasu's arteritis and 156 healthy individuals in the Japanese population were examined for HLA-B specificity at the DNA level by DNA typing using polymerase chain reaction (PCR)/sequence-specific oligonucleotide probe (SSOP) analysis and by subsequent sequencing analysis. The frequency of epitope combination group-B52 (EC-B52) corresponding precisely to HLA-B52 specificity and that of EC-B39.2 which is a newly-identified subtype of HLA-B39 specificity were increased in the patient group. These two disease-associated HLA-B alleles share an epitope composed of 63Glu and 67Ser. Because two HLA-B alleles, HLA-B51 and B39.1, which are similar but different at the epitope from HLA-B52 and B39.2, respectively, are not associated with Takayasu arteritis, 63Glu and 67Ser are supposed to be involved in the pathogenesis.

HLA-linked susceptibility and resistance to Takayasu arteritis

To investigate genetic factors involved in the pathogenesis of Takayasu arteritis, patients in the Japanese population were examined for HLA-A, -B, and -C alleles by serological typing and for HLA-DR, DQ, and DP alleles by DNA typing using polymerase chain reaction (PCR)/sequence-specific oligonucleotide probe (SSOP) analysis. The frequencies of HLA-Bw52, DRB1*1502, DRB5*0102, DQA1*0103, DQB1*0601, and DPB1*0901 alleles were significantly increased and the frequencies of HLA-Bw54, DRB1*0405, DRB4*0101, DQA1*0301, and DQB1*0401 alleles were significantly decreased. Strong linkage disequilibria among the increased alleles and among the decreased alleles were evident in the Japanese population. Therefore, the haplotype of HLA-B252-DRB1*1502-DRB5*0102-DQA1*0103-DQB1++ +*0601-DPA1*02-DPB1*0901 may confer susceptibility to Takayasu arteritis while another haplotype of HLA-Bw54-DRB1*0405-DRB4*0101-DQA1*0301-DQB1++ +*0401 may confer resistance to the disease. These observations clearly indicate that HLA-linked gene(s) are involved in the development of Takayasu arteritis.

HLA-DP antigen and Takayasu arteritis

Sixty-four patients with Takayasu arteritis and 317 healthy individuals in the Japanese population were examined for HLA-A, -B and -C alleles by serological typing and for HLA-DR, DQ and DP alleles by DNA typing using PCR/SSOP analysis. The frequencies of HLA-Bw52, DRB1*1502, DRB5*0102, DQA1*0103, DQB1*0601 and DPB1*0901 alleles were significantly increased and the frequencies of HLA-Bw54, DRB1*0405, DRB4*0101, DQA1*0301, DQB1*0401 alleles were significantly decreased. Strong linkage disequilibria among the increased alleles and among the decreased alleles were evident in the Japanese population. Therefore, the combination or haplotype of HLA-Bw52-DRB1*1502-DRB5*0102-DQA1*0103-DQB1*0601 -DPA1*02-DPB1*0901 may confer susceptibility to Takayasu arteritis while another combination or haplotype of HLA-Bw54-DRB1*0405-DRB4*0101-DQA1*0301-DQB1++ +*0401 may confer resistance to the disease. Because this is the first evidence for the association between an HLA-DP allele and Takayasu arteritis, we examined the nucleotide sequences of the DPB1*0901 allele from a patient and her healthy relatives and found no difference. The disease is therefore not caused by a mutated DPB1 gene.

HLA Typing of Takayasu arteritis in Korea

Takayasu arteritis occurs with a strong predilection for women and particular geographic areas, and as related to the etiology of the disease, association of HLA antigens has been suggested. In the present study, the authors investigated the association of Takayasu arteritis with class I and class II HLA antigens in 59 Korean patients with this disease. Increased frequencies of HLA-Bw52 (chi 2 6.213, P < 0.02), Cw6 (chi 2 4.132, P < 0.05), DR7 (chi 2 4.506, P < 0.04), and DQw2 (chi 2 7.327, P < 0.01) were observed in the patient group as compared to the control group of healthy Koreans. In the Korean population, 2 risk factors in the HLA system for developing this disease appear to be (1) Bw52 and (2) DR7 and a probable haplotype of Cw6, B13, DR7, DQw2. Previous studies of the Japanese population revealed association of Bw52 and class II HLA antigens (DR2, Dw12), which are in linkage disequilibrium with Bw52. It is of interest that in the Korean population, class II antigens (DR7, DQw2), which are not linked to BW52, are associated with the disease. This finding suggests that the disease susceptibility gene of Takayasu arteritis is located between the HLA-B locus and HLA-DR, DQ loci.