Advertisement
Browse Subject Areas
?

Click through the PLOS taxonomy to find articles in your field.

For more information about PLOS Subject Areas, click here.

  • Loading metrics

Lack of an Association of PD-1 and Its Ligand Genes with Behcet's Disease in a Chinese Han Population

  • Qianli Meng ,

    Contributed equally to this work with: Qianli Meng, Haike Guo

    Affiliation Department of Ophthalmology, Guangdong Eye Institute, Guangdong General Hospital, Guangdong Academy of Medical Sciences, Guangzhou, People's Republic of China

  • Haike Guo ,

    Contributed equally to this work with: Qianli Meng, Haike Guo

    Affiliation Department of Ophthalmology, Guangdong Eye Institute, Guangdong General Hospital, Guangdong Academy of Medical Sciences, Guangzhou, People's Republic of China

  • Shengping Hou,

    Affiliation The First Affiliated Hospital of Chongqing Medical University, Chongqing Key Laboratory Of Ophthalmology, Chongqing, People's Republic of China

  • Zhengxuan Jiang,

    Affiliation The First Affiliated Hospital of Chongqing Medical University, Chongqing Key Laboratory Of Ophthalmology, Chongqing, People's Republic of China

  • Aize Kijlstra,

    Affiliation Eye Research Institute Maastricht, Department of Ophthalmology, University Hospital Maastricht, Maastricht, The Netherlands

  • Peizeng Yang

    peizengycum@126.com

    Affiliation The First Affiliated Hospital of Chongqing Medical University, Chongqing Key Laboratory Of Ophthalmology, Chongqing, People's Republic of China

Lack of an Association of PD-1 and Its Ligand Genes with Behcet's Disease in a Chinese Han Population

  • Qianli Meng, 
  • Haike Guo, 
  • Shengping Hou, 
  • Zhengxuan Jiang, 
  • Aize Kijlstra, 
  • Peizeng Yang
PLOS
x

Abstract

Background

Behcet's disease is a chronic, multi-systemic autoimmune disease. Programmed cell death 1 (PD-1) gene is one of non-human leucocyte antigen genes. It has been demonstrated to be associated with several autoimmune diseases. However, only a few studies have addressed the association of ligand genes of PD-1, PD-L1 and PD-L2 with autoimmune disease. The purpose of this study was to analyze the potential association of the PD-1 and its ligand genes with Behcet's disease in a Chinese Han population.

Methodology/Principal Findings

Four single-nucleotide polymorphism (SNPs) rs2227981 and rs10204525 of PD-1, rs1970000 of PD-L1 and rs7854303 of PD-L2 were genotyped in 405 Behcet's patients and 414 age-, sex-, ethnic-matched healthy controls using polymerase chain reaction-restriction fragment length polymorphism assay. The results revealed that there were no significant differences in the genotype and allele frequencies of PD-1 rs2227981 and rs10204525 between the Behcet's patients and controls. A similar result was found for PD-L1 rs1970000 versus healthy controls. Only the C allele and the CC genotype of PD-L2 rs7854303 were identified in patients and controls. Stratification analysis based on gender and clinical findings did not show any associations between PD-1 or its ligand polymorphisms and Behcet's disease.

Conclusions/Significance

None of the currently studied SNPs, PD-1 rs2227981 and rs10204525, PD-L1 rs1970000 and PD-L2 rs7854303, are associated with the susceptibility to Behcet's disease in a Chinese Han population. More studies are needed to confirm these findings in Behcet's patients with other ethnic backgrounds.

Introduction

Behcet's disease is a chronic autoimmune disease characterized by uveitis, recurrent oral aphthae, genital ulcerations and multiform skin lesions [1]. It is quite common in countries along the ancient ‘Silk Road’ that extends from the Far East to the Mediterranean Sea, such as China, Japan and Turkey [1][3]. Although the precise pathogenesis of Behcet's disease remains unclear, extensive studies suggest that an autoimmune response and genetic factors are both involved in this disease. The human leucocyte antigen B51 (HLA-B51) gene is demonstrated to be the strongest indicator for this disease in a variety of ethnic groups [4][7], but it only partly accounts for the genetic predisposition to Behcet's disease. Therefore, the role of non-human leucocyte antigen genes, especially those regulating the immune response, has recently been investigated by various laboratories. Immune response genes such as the tumor necrosis factor alpha (TNF-α) gene [8], SUMO4 gene [9] and IL-23R gene [10], have been reported to be associated with Behcet's disease.

Programmed cell death 1 (PD-1) gene is one of non-human leucocyte antigen genes, located in chromosome 2q37.3 and plays an important role in the regulation of the immune response [11]. The ligands for PD-1 gene were identified as programmed cell death-1 ligand 1 (PD-L1) and programmed cell death-1 ligand 2 (PD-L2), both of which are located in 9p24 [11]. PD-1 and its ligands belong to the CD28:B7 family. PD-1 contains an immunoreceptor tyrosine-based inhibiting motif (ITIM) and an immunoreceptor tyrosine-based switch motif (ITSM) [11], which is expressed on activated T cells, B cells, and myeloid cells [11]. PD-L1 is expressed in T cells, B cells, macrophages, dendritic cells (DCs), and non-lymphoid cells, whereas PD-L2 is observed on activated macrophages, DCs and bone marrow-derived mast cells [11]. Interaction of PD-1 with its ligands could inhibit T-cell receptor-mediated proliferation and cytokine production [11], [12]. PD-1 deficiency results in the development of a lupus-like disease or a dilated cardiomyopathy in animal models [13], [14]. In mice undergoing anterior chamber–associated immune deviation, we found that both mRNA and protein of PD-1, PD-L1 and PD-L2 were markedly upregulated and CD4+PD-1+ T cells exhibited antigen-specific suppressive activity [15]. All these results suggest that PD-1 and its ligands are involved in the regulation of the immune response.

Studies on the PD-1 gene have demonstrated that the polymorphisms of this gene are associated with several autoimmune diseases including systemic lupus erythematosus (SLE) [16][20], rheumatoid arthritis (RA) [21], type I diabetes [22], [23], multiple sclerosis [24], ankylosing spondylitis (AS) [25], and Graves' disease (GD) [26], although there are also some conflicting results [27][32]. However, only few studies have addressed the association of ligand genes of PD-1, PD-L1 and PD-L2, with autoimmune disease [23], [33], [34].

In this study, we extended earlier studies on the association of PD-1, PD-L1 or PD-L2 gene polymorphisms with autoimmune disease, and investigated whether the single-nucleotide polymorphisms (SNPs) rs2227981 and rs10204525 of PD-1, rs1970000 of PD-L1 and rs7854303 of PD-L2 could contribute to the development of Behcet's disease in a Chinese Han population.

Results

The clinical characteristics of the enrolled Behcet's patients were summarized in Table 1. The average age of the Behcet's patients was 32.9±8.9 and that of healthy controls was 31.4±12.5. All Behcet's patients with uveitis had recurrent oral aphthae. The second most common extraocular clinical manifestation was skin lesions, followed by genital ulcerations. Other abnormalities included a positive pathergy test and arthritis. The distribution of genotype frequencies of each SNP in all subjects did not show any significant deviation from the Hardy–Weinberg equilibrium (HWE).

thumbnail
Table 1. Clinical features of the investigated patients with Behcet's disease.

https://doi.org/10.1371/journal.pone.0025345.t001

Genotype and allele frequencies of the analyzed PD-1 rs2227981 and rs10204525, and PD-L1 rs1970000 were depicted in Table 2. Our results showed that there were no significantly differences in the genotype and allele frequencies of rs2227981 and rs10204525 of PD-1 between the Behcet's patients and controls. A similar result was found for rs1970000 of PD-L1 versus healthy controls. The frequency of the GG genotype of rs1970000 tended to be lower in Behcet's patients than in healthy controls (0 versus 1.4%, P = 0.031). However, no difference was found when the Bonferroni correction was applied (Pc = 0.279, n = 9).

thumbnail
Table 2. Genotype and allele frequencies of PD-1, PD-L1 SNPs in Behcet's patients and healthy controls.

https://doi.org/10.1371/journal.pone.0025345.t002

The PD-L2 rs7854303 T allele could not be found and only the C allele and the CC genotype were identified in our patients and controls of the Chinese Han population.

As male gender was predominant in Behcet's patients, a stratification analysis according to gender was also performed. The result showed that there was no association of gender with the four SNPs. When the genotype and allele frequencies were analyzed according to the clinical features, our results showed that any of four SNPs was not found to be associated with any of the extraocular findings including oral aphthae, genital ulcerations, skin lesions, positive pathergy test, or arthritis.

Discussion

This study did not detect an association between Behcet's disease and known polymorphisms of PD-1 and its ligand genes in a Chinese Han population. The selection of SNPs used in our study was principally based on polymorphisms used in earlier studies. PD-1 rs2227981 polymorphism occurs in an exon which affects protein synthesis [25]. rs2227981 and rs10204525 of PD-1 have been found to be associated with SLE, AS or RA [19], [25], [27]. Our previous study has demonstrated that PD-1 rs2227981 may be negatively associated with the extraocular manifestations of Vogt-Koyanagi-Harada syndrome in a Chinese Han population [32]. Although the PD-L1 rs1970000 polymorphism locates in intron 4, which does not affect an amino acid substitution, it may be close to or within transcriptional factor-binding sites [23] and may thus influence the expression of the PD-L1 gene through modifying the binding affinity of transcriptional factors [34]. This polymorphism has been shown to be associated with GD in Japanese patients [34]. PD-L2 rs7854303 C encodes a serine in the transmembrane region, while PD-L2 rs7854303 T encodes a phenylalanine. The transmembrane domain may regulate the expression of the protein molecule on the cell surface [35] and plays a role in dimerization or oligomerization of cell surface molecules [36]. The genotype frequency of PD-L2 rs7854303 T/T has been reported to be significantly increased in patients with SLE [33].

In order to ensure the analysis results, the following attempts were made. First, all genotype distributions of four SNPs in healthy controls were tested and found to be in Hardy–Weinberg equilibrium. Second, the controls and patients were strictly matched according to the gender and the places where they were born to exclude the possible influence of stratification of the population. Behcet's patients of Chinese Han descendents were also strictly selected in this study to avoid the influence of genetic background. Third, a total of 405 Behcet's patients and 414 age-, sex-, ethnically-matched healthy controls were used in this study, and the number of tested samples was large enough to avoid a bias of the results. Finally, 20% of the samples were randomly chosen and analyzed by direct sequencing to validate the genotype findings. In this study, however, we did not find any association of PD-1 rs2227981 and rs10204525, PD-L1 rs197000 and PD-L2 rs7854303 SNPs with Behcet's disease. These results are in disagreement to those seen in other autoimmune diseases reported among different ethnic groups [16][27], [33], [34]. This may be explained by the fact that the etiology and pathogenesis of Behcet's disease may be different from other autoimmune diseases [3]. In view of the fact that PD-1 and its ligands are mainly involved in the adaptive immune response, the lack of an association of PD-1 and its ligands with Behcet's disease presented in this study may provide additional evidence to the current opinion that this disease is an autoinflammatory disease rather than an autoimmune disease [37], [38].

Several previous studies have shown that there is a large variation in the frequencies of PD-1 polymorphisms among different ethnic groups. In the present study, we found a higher frequency of the PD-1 rs10204525 A allele in Chinese (65%) than in Caucasican (8.8%–11.5%) [16], [17], [22] and Mexican (46%) [16]. However, the frequency of the PD-1 rs2227981 C allele in Chinese was comparable with the frequency in Caucasican [16], [17], [22], Mexican [16] and Korean [25] (Table 3). With regards to the association of PD-L2 rs7854303 polymorphism with autoimmune disease, a study by Wang et al. [33] showed that an rs7854303 polymorphism was positively associated with SLE in Taiwanese patients. Their study revealed that the frequencies of the T/T genotype and T allele were significantly higher in the patients with SLE than that of the controls. The frequencies of the C/C, C/T and T/T genotype were 48.1%, 35.0% and 16.9% respectively, and the C and T allele frequencies were 65.6% and 34.4% in their 160 controls. However, conflicting results were observed among the Chinese Han population. Only the CC genotype and C allele of PD-L2 rs7854303 were identified in all Behcet's patients and controls in our study, which showed that the polymorphism of PD-L2 rs7854303 was not associated with Behcet's disease in Chinese Han population.

thumbnail
Table 3. Differences in allele frequencies of PD-1 rs2227981 and rs10204525 among different ethnic groups.

https://doi.org/10.1371/journal.pone.0025345.t003

In summary, to the best of our knowledge, this is the first polymorphism analysis of PD-1 and its ligand genes with Behcet's disease in a Chinese Han population. This study did not detect an association between Behcet's disease and known polymorphisms of PD-1 and its ligand genes in a Chinese Han population. A similar result was observed after stratification analysis based on gender and extraocular features. More studies are needed to confirm these findings in Behcet's patients with other ethnic backgrounds and whether other SNPs of PD-1 and its ligand genes are possibly associated with the susceptibility to Behcet's disease.

Materials and Methods

Clinical Samples

Four hundred and five Behcet's disease patients who all belong to the Chinese Han population were recruited in this study. Four hundred and fourteen age-, sex-, ethnically-matched healthy controls were mainly the accompanying persons or spouses of the patients. All patients were recruited from the First Affiliated Hospital of Chongqing Medical University (Chongqing, China) or the Uveitis Study Center of the Sun Yat-sen University (Guangzhou, China). The diagnosis of Behcet's disease was based on the criteria of the International Study Group [40].

Ethics statement

The protocol was approved by the Ethics Committee of the First Affiliated Hospital of Chongqing Medical University, Chongqing, China (Permit Number: 2009-201004), and written informed consent was obtained from all the study subjects.

Genomic DNA extraction and genotyping

Genomic DNA was isolated from peripheral blood of patients and controls using the commercial Qiamp DNA Blood Mini Kit (Qiagen, Valencia, CA). Amplification of the target DNA was performed by polymerase chain reaction (PCR). The primers used in this study are presented in Table 4. A 15 µl reaction mixture, which consisted of 7.5 µl GoTaq Green Mater Mix (Promega, Madison, WI), 50 pmoles primers, and 0.2 µg of genomic DNA, was amplified by PCR. PCR conditions were as follows: initial denaturation at 95°C for 3 min followed by 35 cycles of denaturation at 94°C for 30 s, annealing at different temperatures (63°C for rs2227981, rs10204525 and rs1970000, and 58°C for rs7854303) for 30 s, extension at 72°C for 30 s, and a final extension at 72°C for 3 min. The SNPs were genotyped by PCR-restriction fragment length polymorphism (RFLP) analysis. The PCR products of four SNPs were respectively digested with 2 U of Pvu II (Promega, Madison, WI), Hsp92 II (Promega, Madison, WI), Ban II (Promega, Madison, WI) and Mnl I (Fermentas, MBI) restriction enzymes (Table 4) in a 10 µl reaction volume overnight. Digestion products were visualized on 3% agarose gels and stained with GoldView™ (SBS Genetech, Beijing, China). To confirm the accuracy of the method employed, randomly selected subjects (20% of all samples) were analyzed by direct sequencing (Invitrogen Biotechnology Co., Guangzhou, China). Appropriate controls (no template and known genotype) were included in each typing run.

Statistical methods

HWE was tested using the χ2 test. Allele frequencies were estimated by direct counting. Allele and genotype frequencies were compared between patients and controls by the χ2 test using SPSS (version 16.0; SPSS Inc., Chicago, IL). The P values were corrected (Pc) with the Bonferroni correction by multiplying with the number of analyses performed. Pc<0.05 was considered significant.

Author Contributions

Conceived and designed the experiments: PY QM HG. Performed the experiments: QM HG. Analyzed the data: QM HG SH. Contributed reagents/materials/analysis tools: PY SH ZJ. Wrote the paper: QM HG PY AK.

References

  1. 1. Sakane T, Takeno M, Suzuki N, Inaba G (1999) Behçet's disease. N Engl J Med 341: 1284–1291.T. SakaneM. TakenoN. SuzukiG. Inaba1999Behçet's disease.N Engl J Med34112841291
  2. 2. Keino H, Okada AA (2007) Behcet's disease: global epidemiology of an Old Silk Road disease. Br J Ophthalmol 91: 1573–1574.H. KeinoAA Okada2007Behcet's disease: global epidemiology of an Old Silk Road disease.Br J Ophthalmol9115731574
  3. 3. Yang P, Fang W, Meng Q, Ren Y, Xing L, et al. (2008) Clinical features of Chinese patients with Behcet's disease. Ophthalmology 115: 312–318.P. YangW. FangQ. MengY. RenL. Xing2008Clinical features of Chinese patients with Behcet's disease.Ophthalmology115312318
  4. 4. Verity DH, Marr JE, Ohno S, Wallace GR, Stanford MR (1999) Behçet's disease, the Silk Road and HLA-B51: historical and geographical perspectives. Tissue Antigens 54: 213–220.DH VerityJE MarrS. OhnoGR WallaceMR Stanford1999Behçet's disease, the Silk Road and HLA-B51: historical and geographical perspectives.Tissue Antigens54213220
  5. 5. Mizuki N, Yabuki K, Ota M, Katsuyama Y, Ando H, et al. (2002) Analysis of microsatellite polymorphism around the HLA-B locus in Iranian patients with Behcet's disease. Tissue Antigens 60: 396–399.N. MizukiK. YabukiM. OtaY. KatsuyamaH. Ando2002Analysis of microsatellite polymorphism around the HLA-B locus in Iranian patients with Behcet's disease.Tissue Antigens60396399
  6. 6. Cohen R, Metzger S, Nahir M, Chajek-Shaul T (2002) Association of the MIC-A gene and HLA-B51 with Behcet's disease in Arabs and non-Ashkenazi Jews in Israel. Ann Rheum Dis 61: 157–160.R. CohenS. MetzgerM. NahirT. Chajek-Shaul2002Association of the MIC-A gene and HLA-B51 with Behcet's disease in Arabs and non-Ashkenazi Jews in Israel.Ann Rheum Dis61157160
  7. 7. Yabuki K, Mizuki N, Ota M, Katsuyama Y, Palimeris G, et al. (1999) Association of MICA gene and HLA-B*5101 with Behcet's disease in Greece. Invest Ophthalmol Vis Sci 40: 1921–1926.K. YabukiN. MizukiM. OtaY. KatsuyamaG. Palimeris1999Association of MICA gene and HLA-B*5101 with Behcet's disease in Greece.Invest Ophthalmol Vis Sci4019211926
  8. 8. Park K, Kim N, Nam J, Bang D, Lee ES (2006) Association of TNFA promoter region haplotype in Behcet's Disease. J Korean Med Sci 21: 596–601.K. ParkN. KimJ. NamD. BangES Lee2006Association of TNFA promoter region haplotype in Behcet's Disease.J Korean Med Sci21596601
  9. 9. Hou S, Yang P, Du L, Zhou H, Lin X, et al. (2008) SUMO4 gene polymorphisms in Chinese Han patients with Behcet's disease. Clin Immunol 129: 170–175.S. HouP. YangL. DuH. ZhouX. Lin2008SUMO4 gene polymorphisms in Chinese Han patients with Behcet's disease.Clin Immunol129170175
  10. 10. Jiang Z, Yang P, Hou S, Du L, Xie L, et al. (2010) IL-23R gene confers susceptibility to Behcet's disease in a Chinese Han population. Ann Rheum Dis 69: 1325–1328.Z. JiangP. YangS. HouL. DuL. Xie2010IL-23R gene confers susceptibility to Behcet's disease in a Chinese Han population.Ann Rheum Dis6913251328
  11. 11. Keir ME, Butte MJ, Freeman GJ, Sharpe AH (2008) PD-1 and its ligands in tolerance and immunity. Ann Rev Immunol 26: 677–704.ME KeirMJ ButteGJ FreemanAH Sharpe2008PD-1 and its ligands in tolerance and immunity.Ann Rev Immunol26677704
  12. 12. Okazaki T, Maeda A, Nishimura H, Kurosaki T, Honjo T (2001) PD-1 immunoreceptor inhibits B cell receptor-mediated signaling by recruiting src homology 2-domain-containing tyrosine phosphatase 2 to phosphotyrosine. Proc Natl Acad Sci U S A 98: 13866–13871.T. OkazakiA. MaedaH. NishimuraT. KurosakiT. Honjo2001PD-1 immunoreceptor inhibits B cell receptor-mediated signaling by recruiting src homology 2-domain-containing tyrosine phosphatase 2 to phosphotyrosine.Proc Natl Acad Sci U S A981386613871
  13. 13. Nishimura H, Nose M, Hial H, Minato N, Honjo T (1999) Development of lupus-like autoimmune diseases by disruption of the PD-1 gene encoding an ITIM motif-carrying immunoreceptor. Immunity 11: 141–151.H. NishimuraM. NoseH. HialN. MinatoT. Honjo1999Development of lupus-like autoimmune diseases by disruption of the PD-1 gene encoding an ITIM motif-carrying immunoreceptor.Immunity11141151
  14. 14. Nishimura H, Okazaki T, Tanaka Y, Nakatani K, Hara M, et al. (2001) Autoimmune dilated cardiomyopathy in PD-1 receptor-deficient mice. Science 291: 319–322.H. NishimuraT. OkazakiY. TanakaK. NakataniM. Hara2001Autoimmune dilated cardiomyopathy in PD-1 receptor-deficient mice.Science291319322
  15. 15. Meng Q, Yang P, Li B, Zhou H, Huang X, et al. (2006) CD4+PD-1+ T cells act as regulatory cells during the induction of anterior chamber-associated immune deviation. Invest Ophthalmol Vis Sci 47: 4444–4452.Q. MengP. YangB. LiH. ZhouX. Huang2006CD4+PD-1+ T cells act as regulatory cells during the induction of anterior chamber-associated immune deviation.Invest Ophthalmol Vis Sci4744444452
  16. 16. Prokunina L, Castillejo-Lopez C, Oberg F, Gunnarsson I, Berg L, et al. (2002) A regulatory polymorphism in PDCD1 is associated with susceptibility to systemic lupus erythematosus in humans. Nat Genet 32: 666–669.L. ProkuninaC. Castillejo-LopezF. ObergI. GunnarssonL. Berg2002A regulatory polymorphism in PDCD1 is associated with susceptibility to systemic lupus erythematosus in humans.Nat Genet32666669
  17. 17. Ferreiros-Vidal I, Gomez-Reino JJ, Barros F, Carracedo A, Carreira P, et al. (2004) Association of PDCD1 with susceptibility to systemic lupus erythematosus: evidence of population-specific effects. Arthritis Rheum 50: 2590–2597.I. Ferreiros-VidalJJ Gomez-ReinoF. BarrosA. CarracedoP. Carreira2004Association of PDCD1 with susceptibility to systemic lupus erythematosus: evidence of population-specific effects.Arthritis Rheum5025902597
  18. 18. Sanghera DK, Manzi S, Bontempo F, Nestlerode C, Kamboh MI (2004) Role of an intronic polymorphism in the PDCD1 gene with the risk of sporadic systemic lupus erythematosus and the occurrence of antiphospholipid antibodies. Hum Genet 115: 393–398.DK SangheraS. ManziF. BontempoC. NestlerodeMI Kamboh2004Role of an intronic polymorphism in the PDCD1 gene with the risk of sporadic systemic lupus erythematosus and the occurrence of antiphospholipid antibodies.Hum Genet115393398
  19. 19. Thorburn CM, Prokunina-Olsson L, Sterba KA, Lum RF, Seldin MF, et al. (2007) Association of PDCD1 genetic variation with risk and clinical manifestations of systemic lupus erythematosus in a multiethnic cohort. Genes Immun 8: 279–287.CM ThorburnL. Prokunina-OlssonKA SterbaRF LumMF Seldin2007Association of PDCD1 genetic variation with risk and clinical manifestations of systemic lupus erythematosus in a multiethnic cohort.Genes Immun8279287
  20. 20. Velazquez-Cruz R, Orozco L, Espinosa-Rosales F, Carreno-Manjarrez R, Solis-Vallejo E, et al. (2007) Association of PDCD1 polymorphisms with childhood-onset systemic lupus erythematosus. Eur J Hum Genet 15: 336–341.R. Velazquez-CruzL. OrozcoF. Espinosa-RosalesR. Carreno-ManjarrezE. Solis-Vallejo2007Association of PDCD1 polymorphisms with childhood-onset systemic lupus erythematosus.Eur J Hum Genet15336341
  21. 21. Kong EK, Prokunina-Olsson L, Wong WH, Lau CS, Chan TM, et al. (2005) A new haplotype of PDCD1 is associated with rheumatoid arthritis in Hong Kong Chinese. Arthritis Rheum 52: 1058–1062.EK KongL. Prokunina-OlssonWH WongCS LauTM Chan2005A new haplotype of PDCD1 is associated with rheumatoid arthritis in Hong Kong Chinese.Arthritis Rheum5210581062
  22. 22. Nielsen C, Hansen D, Husby S, Jacobsen BB, Lillevang ST (2003) Association of a putative regulatory polymorphism in the PD-1 gene with susceptibility to type 1 diabetes. Tissue Antigens 62: 492–497.C. NielsenD. HansenS. HusbyBB JacobsenST Lillevang2003Association of a putative regulatory polymorphism in the PD-1 gene with susceptibility to type 1 diabetes.Tissue Antigens62492497
  23. 23. Ni R, Ihara K, Miyako K, Kuromaru R, Inuo M, et al. (2007) PD-1 gene haplotype is associated with the development of type 1 diabetes mellitus in Japanese children. Hum Genet 121: 223–232.R. NiK. IharaK. MiyakoR. KuromaruM. Inuo2007PD-1 gene haplotype is associated with the development of type 1 diabetes mellitus in Japanese children.Hum Genet121223232
  24. 24. Kroner A, Mehling M, Hemmer B, Rieckmann P, Toyka KV, et al. (2005) A PD-1 polymorphism is associated with disease progression in multiple sclerosis. Ann Neurol 58: 50–57.A. KronerM. MehlingB. HemmerP. RieckmannKV Toyka2005A PD-1 polymorphism is associated with disease progression in multiple sclerosis.Ann Neurol585057
  25. 25. Lee SH, Lee YA, Woo DH, Song R, Park EK, et al. (2006) Association of the programmed cell death 1 (PDCD1) gene polymorphism with ankylosing spondylitis in the Korean population. Arthritis Res Ther 8: R163.SH LeeYA LeeDH WooR. SongEK Park2006Association of the programmed cell death 1 (PDCD1) gene polymorphism with ankylosing spondylitis in the Korean population.Arthritis Res Ther8R163
  26. 26. Newby PR, Roberts-Davies EL, Brand OJ, Heward JM, Franklyn JA, et al. (2007) Tag SNP screening of the PDCD1 gene for association with Graves' disease. Clin Endocrinol (Oxf) 67: 125–128.PR NewbyEL Roberts-DaviesOJ BrandJM HewardJA Franklyn2007Tag SNP screening of the PDCD1 gene for association with Graves' disease.Clin Endocrinol (Oxf)67125128
  27. 27. Lin SC, Yen JH, Tsai JJ, Tsai WC, Ou TT, et al. (2004) Association of a programmed death 1 gene polymorphism with the development of rheumatoid arthritis, but not systemic lupus erythematosus. Arthritis Rheum 50: 770–775.SC LinJH YenJJ TsaiWC TsaiTT Ou2004Association of a programmed death 1 gene polymorphism with the development of rheumatoid arthritis, but not systemic lupus erythematosus.Arthritis Rheum50770775
  28. 28. Abelson AK, Johansson CM, Kozyrev SV, Kristjansdottir H, Gunnarsson I, et al. (2007) No evidence of association between genetic variants of the PDCD1 ligands and SLE. Genes Immun 8: 69–74.AK AbelsonCM JohanssonSV KozyrevH. KristjansdottirI. Gunnarsson2007No evidence of association between genetic variants of the PDCD1 ligands and SLE.Genes Immun86974
  29. 29. Fawwaz S, Nikamo P, Torn C, Landin-Olsson M, Lernmark A, et al. (2007) No evidence of association of the PDCD1 gene with Type 1 diabetes. Diabet Med 24: 1473–1477.S. FawwazP. NikamoC. TornM. Landin-OlssonA. Lernmark2007No evidence of association of the PDCD1 gene with Type 1 diabetes.Diabet Med2414731477
  30. 30. Ferreiros-Vidal I, D'Alfonso S, Papasteriades C, Skopouli FN, Marchini M, et al. (2007) Bias in association studies of systemic lupus erythematosus susceptibility due to geographical variation in the frequency of a programmed cell death 1 polymorphism across Europe. Genes Immun 8: 138–146.I. Ferreiros-VidalS. D'AlfonsoC. PapasteriadesFN SkopouliM. Marchini2007Bias in association studies of systemic lupus erythematosus susceptibility due to geographical variation in the frequency of a programmed cell death 1 polymorphism across Europe.Genes Immun8138146
  31. 31. Iwamoto T, Ikari K, Inoue E, Toyama Y, Hara M, et al. (2007) Failure to confirm association between PDCD1 polymorphisms and rheumatoid arthritis in a Japanese population. J Hum Genet 52: 557–560.T. IwamotoK. IkariE. InoueY. ToyamaM. Hara2007Failure to confirm association between PDCD1 polymorphisms and rheumatoid arthritis in a Japanese population.J Hum Genet52557560
  32. 32. Meng Q, Liu X, Yang P, Hou S, Du L, et al. (2009) PD-1 genes may protect against extra-ocular manifestations in Chinese Han patients with Vogt-Koyanagi-Harada syndrome. Mol Vis 15: 386–392.Q. MengX. LiuP. YangS. HouL. Du2009PD-1 genes may protect against extra-ocular manifestations in Chinese Han patients with Vogt-Koyanagi-Harada syndrome.Mol Vis15386392
  33. 33. Wang SC, Lin CH, Ou TT, Wu CC, Tsai WC, et al. (2007) Ligands for programmed cell death 1 gene in patients with systemic lupus erythematosus. J Rheumatol 34: 721–725.SC WangCH LinTT OuCC WuWC Tsai2007Ligands for programmed cell death 1 gene in patients with systemic lupus erythematosus.J Rheumatol34721725
  34. 34. Hayashi M, Kouki T, Takasu N, Sunagawa S, Komiya I (2008) Association of an A/C single nucleotide polymorphism in programmed cell death-ligand 1 gene with Graves' disease in Japanese patients. Eur J Endocrinol 158: 817–822.M. HayashiT. KoukiN. TakasuS. SunagawaI. Komiya2008Association of an A/C single nucleotide polymorphism in programmed cell death-ligand 1 gene with Graves' disease in Japanese patients.Eur J Endocrinol158817822
  35. 35. Chou WC, Liao KW, Lo YC, Jiang SY, Yeh MY, et al. (1999) Expression of chimeric monomer and dimer proteins on the plasma membrane of mammalian cells. Biotechnol Bioeng 65: 160–169.WC ChouKW LiaoYC LoSY JiangMY Yeh1999Expression of chimeric monomer and dimer proteins on the plasma membrane of mammalian cells.Biotechnol Bioeng65160169
  36. 36. Choi S, Lee E, Kwon S, Park H, Yi JY, et al. (2005) Transmembrane domain-induced oligomerization is crucial for the functions of syndecan-2 and syndecan-4. J Biol Chem 280: 42573–42579.S. ChoiE. LeeS. KwonH. ParkJY Yi2005Transmembrane domain-induced oligomerization is crucial for the functions of syndecan-2 and syndecan-4.J Biol Chem2804257342579
  37. 37. Gül A (2005) Behcet's disease as an autoinflammatory disorder. Curr Drug Targets Inflamm Allergy 4: 81–83.A. Gül2005Behcet's disease as an autoinflammatory disorder.Curr Drug Targets Inflamm Allergy48183
  38. 38. Direskeneli H (2006) Autoimmunity vs autoinflammation in Behcet's disease: do we oversimplify a complex disorder? Rheumatology (Oxford) 45: 1461–465.H. Direskeneli2006Autoimmunity vs autoinflammation in Behcet's disease: do we oversimplify a complex disorder?Rheumatology (Oxford)451461465
  39. 39. Wang SC, Chen YJ, Ou TT, Wu CC, Tsai WC, et al. (2006) Programmed death-1 gene polymorphisms in patients with systemic lupus erythematosus in Taiwan. J Clin Immunol 26: 506–511.SC WangYJ ChenTT OuCC WuWC Tsai2006Programmed death-1 gene polymorphisms in patients with systemic lupus erythematosus in Taiwan.J Clin Immunol26506511
  40. 40. International Study Group for Behcet's Disease (1990) Criteria for diagnosis of Behcet's disease. Lancet 335: 1078–1080.International Study Group for Behcet's Disease1990Criteria for diagnosis of Behcet's disease.Lancet33510781080