Cytomegalovirus in autoimmunity: T cell crossreactivity to viral antigen and autoantigen glutamic acid decarboxylase

Antigens of pathogenic microbes that mimic autoantigens are thought to be responsible for the activation of autoreactive T cells. Viral infections have been associated with the development of the neuroendocrine autoimmune diseases type 1 diabetes and stiff-man syndrome, but the mechanism is unknown. These diseases share glutamic acid decarboxylase (GAD65) as a major autoantigen. We screened synthetic peptide libraries dedicated to bind to HLA-DR3, which predisposes to both diseases, using clonal CD4(+) T cells reactive to GAD65 isolated from a prediabetic stiff-man syndrome patient. Here we show that these GAD65-specific T cells crossreact with a peptide of the human cytomegalovirus (hCMV) major DNA-binding protein. This peptide was identified after database searching with a recognition pattern that had been deduced from the library studies. Furthermore, we showed that hCMV-derived epitope can be naturally processed by dendritic cells and recognized by GAD65 reactive T cells. Thus, hCMV may be involved in the loss of T cell tolerance to autoantigen GAD65 by a mechanism of molecular mimicry leading to autoimmunity.     

谷氨酸脱羧酶（GAD65）自身抗体的放射配体检测法

为建立一种诊断和预测胰岛素依赖型糖尿病（ＩＤＤＭ）的免疫学定量检测指标，改良了Ｐｅ－ｔｅｒｓｅｎ的谷氨酸脱羧酶自身抗体（ＧＡＤ－Ａｂ）放射配体分析法，以试管内转录和翻译的标记６５ｋＤ谷氨酸脱羧酶作抗原，以蛋白Ａ凝胶作为抗体沉淀剂，用液闪仪测ｃｐｍ值。对１５例初发ＩＤＤＭ和４０例对照的测定结果显示：ＩＤＤＭ组ｃｐｍ值显著高于对照组（Ｐ＜０．００１）；以对照组ｘ±２ｓ作为阳性标准，则ＩＤＤＭ组阳性率为６７％（１０／１５），对照组为２．５％（１／４０）。故改良的ＧＡＤ－Ａｂ放射配体分析法对初发ＩＤＤＭ诊断的特异性为９７．５％，敏感性为６７％。且操作简便，易于推广。     

Development of autoimmune diabetes in glutamic acid decarboxylase 65 (GAD65) knockout NOD mice

Aims/hypothesis Type 1 diabetes mellitus, a T-cell-mediated autoimmune disease, results from the selective destruction of insulin-producing pancreatic beta cells. Autoantibodies against beta-cell components are used clinically as sensitive markers of this disease; however, their physiological role has not been clear. To investigate the role of glutamic acid decarboxylase 65 (GAD65) in the development of the Type 1 diabetes of non-obese diabetic (NOD) mice, we analysed and characterised NOD mice with targeted disruption of the GAD65 gene.Methods GAD65-deficient mice were previously established. After backcrossing the knockout mutation onto the NOD genetic background for up to eight generations, female littermates of the three resulting genotypes were produced by intercrossing: GAD65 +/+ (n=23), GAD65 +/– (n=62), and GAD65 –/– (n=31).Results The cumulative incidence of autoimmune diabetes showed no significant difference among the three groups in longitudinal studies using the Kaplan-Meier method. Islet morphology showed that the progression of islet infiltration did not differ significantly between the three groups.Conclusion/interpretation The cumulative incidence of autoimmune diabetes was not influenced by the GAD65 deficiency. These data suggest that GAD65 is not a major regulatory target of beta-cell autoimmunity in NOD mice.Abbreviations NOD Non-obese diabetic     

Diagnostic sensitivity of immunodominant epitopes of glutamic acid decarboxylase (GAD65) autoantibodies in childhood IDDM

Summary The prevalence and titre of epitope-specific autoantibodies to glutamic acid decarboxylase (GAD65) in 155 insulin-dependent diabetic (IDDM) and 9 GAD65 antibody (Ab)-positive healthy children were determined using four GAD65/67 chimaeric molecules which discriminate among the N-terminal (N), middle (M) and C-terminal (C) epitopes of GAD65. Radioligand binding assays for IgG Ab used immunoprecipitation of in vitro translated ³⁵S-GAD. We found autoantibodies to GAD65 in 116 of 155 (75%), to GAD67 in 19 of 155 (12%) (p<0.0001) and to the GAD65-N-67 chimaera in 25 of 155 (16%) (p<0.0001) IDDM sera. GAD67Ab were found almost exclusively (17 of 19, 89%) in GAD65Ab-positive sera and the levels of GAD67Ab correlated with those of GAD65Ab (r ²=0.5913; p=0.009). GAD65Ab directed to GAD65-M were found in 104 of 155 (67%), to GAD65-C in 104 of 155 (67%) and to GAD65-M + C in 116 of 155 (75%) of IDDM sera, and indicated reactivity to at least two distinct epitopes. Among the nine GAD65Ab-positive healthy children, two (22%) were also positive with GAD67, nine (100%) with GAD65-M + C, seven (78%) with GAD65-M, eight (89%) with GAD65-C and two (22%) with GAD65-N-67. Titres of GAD65Ab (p=0.007), GAD65-C-Ab (p=0.002) and GAD65C + M-Ab (p=0.003), but not of GAD65-M-Ab (p=0.101) were significantly higher in IDDM than in healthy children. We conclude that GAD65Ab in IDDM and healthy children are directed to middle and C-terminal epitopes, and propose that levels of antibodies specifically directed to the carboxy-terminal end of GAD65 may distinguish IDDM from healthy children.Abbreviations Ab Antibodies - GAD glutamic acid decarboxylase - ICA islet cell antibodies - IDDM insulin-dependent diabetes mellitus - JDF Juvenile Diabetes Foundation - PC-2 proinsulin-converting enzyme 2 - TCA trichloroacetic acid - M middle terminal epitope - N N-terminal epitope - C C-terminal epitope     

谷氨酸脱羧酶抗体水平对两种成人隐匿性自身免疫糖尿病亚型的识别

目的　探讨不同谷氨酸脱羧酶 (GAD65)抗体水平的成人隐匿性自身免疫糖尿病(LADA)患者的临床特点 ,了解LADA患者中是否存在两种不同的亚型。方法　对 750例临床初诊为2型糖尿病 (T2DM)患者及其志愿参加进一步研究的 2 95例患者用放免法进行GAD65抗体 (GADA)测定 ,绘制GADA指数的频数分布图 ,进行各组间临床特点的比较。结果　 (1 )GADA在初诊 2型糖尿病中的阳性率为 9 7% ,高抗体水平者 (GADA指数≥ 0 5)占 2 8%。 (2 )LADA患者中抗体滴度较低(GADA指数 0 0 5～ <0 5)者在胰岛功能 (空腹C肽 50 0pmol/L比 50 4pmol/L ,P >0 0 5)、高血压比例(48 7%比 42 5 % ,P >0 0 5)及体重指数 (2 3 2kg/m2 比 2 2 3kg/m2 ,P >0 0 5)等方面与 2型糖尿病相似 ,即为LADA 2型 ;抗体滴度较高者 (GADA指数≥ 0 5)具有起病年龄小、胰岛功能差、更多使用胰岛素治疗 (P <0 0 1 )等特点 ,临床表现更类似经典的 1型糖尿病 ,即为LADA 1型。结论　LADA患者具有异质性 ,存在LADA 1和LADA 2两种亚型 ,LADA 1型的临床特点更类似于经典的 1型糖尿病     

Murine monoclonal glutamic acid decarboxylase (GAD)65 antibodies recognize autoimmune-associated GAD epitope regions targeted in patients with type 1 diabetes mellitus and Stiff-man syndrome

To study the immune response to glutamic acid decarboxylase (GAD) in insulin-dependent diabetes mellitus, monoclonal GAD antibodies after fusion of splenocytes from a nondiabetes-susceptible BALB/c mouse immunized with human recombinant GAD65 were generated. Of the 44 monoclonals, 35 are specific for the GAD65 isoform, whereas 9 also react with GAD67. Some 37 monoclonals, including all GAD65/67 reactive antibodies, react with GAD by Western blot analysis. The remaining 7 GAD65 monoclonals bind GAD only in an immunoprecipitation assay, which implies that they target epitopes dependent on the conformation of the GAD molecule. The¹²⁵I-GAD binding of the GAD65 monoclonals reactive on Western blotting was significantly diminished by all 3 sera from Stiff-man syndrome patients but only by 3/30 (10%) sera from type 1 diabetic patients. In contrast, the 7 monoclonal antibodies reactive with a conformation-dependent GAD epitope were competitive with 83% of GAD-autoantibody-positive sera from these diabetic patients. Using chimeric GAD65/67 proteins, the epitope region targeted by these monoclonals was mapped to the middle of GAD65 (amino acids 221–442). This central conformation-dependent GAD region was also targeted by sera from patients with type 1 diabetes. In conclusion, our data show that evne after common immunization of a nondiabetes-susceptible mouse strain, monoclonals were obtained which preferentially react with the GAD65 linear amino-terminus (amino acids 4–17) and a conformation-dependent region located in the middle of GAD targeted by autoantibodies, indicating that this GAD region is not restricted to the autoimmune response associated with the Stiff-man syndrome and the bete-cell destruction in type 1 diabetes mellitus.     

Expression of the 64 kDa/glutamic acid decarboxylase rat islet cell autoantigen is influenced by the rate of insulin secretion

Summary This study examined the relationship between insulin secretion and expression of the 64 kDa/glutamic acid decarboxylase autoantigen in pancreatic islets. Islets isolated from Wistar rats were cultured for 3 days under different conditions: in 5.5 mmol/l glucose with or without a-ketoisocaproic acid or glipizide and in 28 mmol/l glucose with or without diazoxide. The 64 kDa/glutamic acid decarboxylase autoantigen was precipitated from lysates of [³⁵S]-methionine-labelled islets with sera from patients with Type 1 (insulin-dependent) diabetes mellitus and identified by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and fluorography. In parallel, insulin contents of the islets and the media were determined as well as the rates of glucose-stimulated (pro)insulin biosynthesis. α-Ketoisocaproic acid and glipi zide were found to stimulate the expression of the 64 kDa/glutamic acid decarboxylase autoantigen and also the rate of insulin secretion. Diazoxide on the other hand reduced the rate of the 64 kDa/glutamic acid decarboxylase autoantigen synthesis in parallel with an inhibition of glucose-stimulated insulin release. Under most of the conditions employed, (pro)insulin biosynthesis was not affected. The correlation found between the rate of insulin release and expression of the 64 kDa/glutamic acid decarboxylase auto-antigen might provide an explanation for the earlier observed relationship between the functional demands on the Beta cells and their rate of destruction which may result in diabetes.     

Cross-reactive rubella virus and glutamic acid decarboxylase (65 and 67) protein determinants recognised by T cells of patients with Type I diabetes mellitus

Aims/hypothesis. To examine the cross-reaction between viral and beta-cell protein determinants and to further understand the potential role of this mechanism in Type I (insulind-dependent) diabetes mellitus.¶Methods. Immune responses to a panel of 28 viral and beta-cell protein peptides representing selected sequences of rubella virus (RV), Coxsackie virus, human 38 KDa31G and glutamic acid decarboxylase (GAD 65 and 67) proteins in proliferation or cytotoxicity assays have been studied using uncloned and cloned T-cell cohorts from a group of 60 Type I diabetic patients.¶Results. Peptide GAD65(252–266) induced the responses of patients with recent onset diabetes in proliferation assays at the highest frequency (77 %), whereas GAD67(212–226) stimulated the cellular responses at the highest rate (61 %) in patients with late-onset diabetes. RVE1(157–176) was recognised by all groups of patients at the highest frequency and the largest amplitude among the viral peptides tested. T-cell clones specific to GAD65(252–266), GAD65(274–286) or GAD67(212–226) were tested in cytotoxicity assays for their responses to rubella virus peptides. Each of these T-cell clones cross-reacted with two to four rubella virus peptides, including RVE1(157–176) and RVE2(87–107). Analysis of the sequences of cross-reactive viral and glutamic acid decarboxylase antigens showed that these epitopes shared similar peptide binding motifs to HLA DR3/DR4. There is a statistically significant correlation between the response amplitude of patient's peripheral blood mononuclear cells to RVE1(157–176), RVE2(87–107) and GAD65(274–286) in patients with recent onset diabetes, and to RVE1(157–176) and GAD67(212–226) in patients with late onset diabetes.¶Conclusion/interpretation. Cross-reactive glutamic acid decarboxylase and rubella virus determinants identified by T-cell clones were also recognised at high frequencies by general T-cell populations of Type I diabetic patients. [Diabetologia (2000) 43: 750–762]     

Limbic encephalitis and type 1 diabetes with glutamic acid decarboxylase 65 (GAD65) autoimmunity: improvement with high-dose intravenous immunoglobulin therapy

Glutamic acid decarboxylase antibodies (GAD-abs) are an immunological factor involved in type 1 diabetes and other diseases involving the central nervous system. This report is of a patient with type 1 diabetes and a rare case of non-paraneoplastic limbic encephalitis mediated by anti-GAD65 antibodies that improved with the use of immunosuppressive drugs.     

Prevention of type I diabetes transfer by glutamic acid decarboxylase 65 peptide 206-220-specific T cells

Glutamic acid decarboxylase (GAD) 65 is one of the major pancreatic antigens targeted by self-reactive T cells in type I diabetes mellitus. T cells specific for GAD65 are among the first to enter inflamed islets and may be important for the initiation of autoimmune diabetes. However, we previously reported that nonobese diabetic (NOD) mice transgenic for a T cell antigen receptor (TCR) specific for one of the immunodominant epitopes of GAD65, peptide 286-300 (G286), are protected from insulitis and diabetes. To examine whether other GAD65-reactive T cells share this phenotype, we have generated TCR transgenic NOD mice for a second immunodominant epitope of GAD65, peptide 206-220 (G206). As in G286 mice, G206 mice do not develop islet inflammation or diabetes. When adoptively transferred along with diabetogenic T cells, activated G206 T cells significantly delayed the onset of diabetes in NOD.scid recipients. Both G206 and G286 T cells produce immunoregulatory cytokines IFN-gamma and IL-10 at low levels when activated by cognate antigens. These data suggest that GAD65-specific T cells may play a protective role in diabetes pathogenesis by regulating pathogenic T cell responses. A better understanding of the functions of autoreactive T cells in type I diabetes will be necessary for choosing desirable targets for immunotherapy.     

人重组谷氨酸脱羧酶65基因的克隆表达及其在1型糖尿病诊断中的初步应用

目的 构建人重组谷氨酸脱羧酶65(GAD65)基因不同区段原核表达载体,诱导表达获得重组蛋白,并初步验证GAD65不同抗原区段在1型糖尿病GAD自身抗体检测中的价值.方法 应用巢式逆转录聚合酶链式反应(RT-PCR)技术调取目的 基因,构建相应的原核表达质粒,转化大肠杆菌E.coli HB101,诱导表达获得纯化重组蛋白,用重组蛋白作为包被抗原,初步建立检测GAD自身抗体的酶联免疫吸附测定法(ELISA)方法,评价各片段在1型糖尿病诊断中的价值.结果 获得了4种可被1型糖尿病患者血清识别的重组人GAD抗原区段,其中GAD65(180-585)抗原区段具有很好的特异性,检出率为55.3%,是首选的抗原区段.结论 所选重组人GAD65(180-585)抗原区段具有良好的抗原性,可作为1型糖尿病患者辅助诊断试剂的候选抗原.     

Recognition of glutamic acid decarboxylase (GAD) by autoantibodies from different GAD antibody-positive phenotypes

Autoantibodies against the smaller isoform of glutamic acid decarboxylase (GAD) are markers for Type 1 diabetes. GAD65 autoantibody (GAD65Ab)-positive individuals in the general population are, however, mostly at low risk of developing Type 1 diabetes, suggesting that GAD65Ab phenotypes may be associated with different underlying pathogenic processes. The aim of this study was to test the hypothesis that Type 1 diabetes patients (n = 243; group I), GAD65Ab-positive healthy individuals (n = 28; group II), and healthy first-degree relatives of Type 1 diabetes patients (n = 41; group III) have antibody phenotypes that recognize different GAD65 epitopes. Sera from groups I-III were tested for their binding to GAD65 and GAD67, as well as six different GAD65/67 fusion proteins. Regardless of group, sera reactive to both GAD65 and GAD67 showed broader epitope reactivity than GAD65-specific sera. Furthermore, Type 1 diabetes patients showed a more restricted epitope binding than healthy individuals and first-degree relatives, demonstrating significantly less binding to the N-terminal part of GAD65 and to GAD67. Our analysis demonstrates that the N-terminal part is essential for full antibody binding to GAD65, in particular, to the middle epitope. It is suggested that Type 1 diabetes is associated with restricted GAD65Ab epitope specificity.     

从猪脑中提取纯化谷氨酸脱羧酶的研究

目的　从猪脑中提取纯化谷氨酸脱羧酶（ Ｇ Ａ Ｄ） ,用于１ 型糖尿病患者 Ｇ Ａ Ｄ 抗体的测定。方法　以猪脑制备 Ｇ Ａ Ｄ 粗酶,经 Ｓｅｐｈａｄｅｘ Ｇ１００ 、 Ｄ Ｅ Ａ Ｅ Ｓｅｐｈａｃｅｌ 和羟基磷灰石凝胶层析分离纯化,结合十二烷基硫酸钠聚丙烯酰胺凝胶电泳（ Ｓ Ｄ Ｓ Ｐ Ａ Ｇ Ｅ） 测定相对分子质量、同位素法测定 Ｇ Ａ Ｄ酶活性,建立了 Ｇ Ａ Ｄ 纯化方法。结果　 Ｇ Ａ Ｄ 粗酶经纯化后的单位蛋白量的酶活性增加了１１８ 倍。经 Ｓ Ｄ Ｓ Ｐ Ａ Ｇ Ｅ 分析,为一条相对分子质量约６４ ０００ 的蛋白条带。结论　用多步层析分离法从猪脑中提取纯化 Ｇ Ａ Ｄ 是一种简便可行的方法。     

Isolation by anion-exchange of immunologically and enzymatically active human islet glutamic acid decarboxylase 65 overexpressed in Sf9 insect cells

Summary The enzymel-glutamic acid decarboxylase is a major autoantigen of the beta cell. Autoantibodies against this enzyme are observed before the onset of insulin-dependent diabetes mellitus (IDDM) in man and may be of predictive value. There is evidence that this enzyme is involved in the development of autoimmune diabetes in animals. In order to facilitate the investigation of the role ofl-glutamine acid decarboxylase in IDDM, we expressed the 65 kDa isoform of human isletl-glutamic acid decarboxylase in insect cells using a baculovirus-based vector. The material was expressed at high levels (up to 50 mg/l of cells). Partially purified metabolically labelledl-glutamic acid decarboxylase bound to immunoglobulins in the sera from 20 of 49 subjects with newly-diagnosed IDDM. The enzyme was isolated in high yields (up to 26 mg/l cell culture) with fully maintained enzymatic activity by either ion-exchange chromatography or immunoaffinity chromatography. Purifiedl-glutamic acid decarboxylase inhibited the binding of radioactivel-glutamic acid decarboxylase, prepared by in vitro translation of mRNA, to immunoglobulins in the sera of subjects with IDDM. Recombinant human isletl-glutamic acid decarboxylase, isolated from Sf9 cells, is a suitable material for the large scale investigation of the utility of this enzyme in the prediction and prevention of autoimmune diabetes. [Diabetologia (1995) 38: 14–23     

Characterization of CD4+ T cells specific for glutamic acid decarboxylase (GAD65) and proinsulin in a patient with stiff‐person syndrome but without type 1 diabetes

Background

Glutamic acid decarboxylase (GAD) is a rate‐limiting enzyme in the synthesis of gamma‐amino butyric acid (GABA) and an important autoantigen both in patients with type 1 diabetes (T1D) and stiff‐person syndrome (SPS). Autoantibodies (GADA) to the 65‐kDa isoform of GAD are a characteristic feature in both diseases. Approximately 30% of patients with SPS develop diabetes, yet, it is unclear to which extent co‐existing autoimmunity to GAD65 and other islet autoantigens determines the risk of developing T1D.

Methods

In this study, we monitored CD4+ T‐cell responses to GAD65 and proinsulin in a patient with SPS who remained normoglycaemic during the 46‐month follow‐up.

Results

Fluctuating but persistent T‐cell reactivity to GAD65 was identified, as well as T‐cell reactivity to proinsulin at one time point. The majority of the T‐cell clones isolated from the patient with SPS produced high levels of Th2 cytokines (IL‐13, IL‐5 and IL‐4). We also examined levels of GADA, insulin and IA‐2 autoantibodies, and epitope specificity of GADA. In both serum and cerebrospinal fluid (CSF), GADA levels were high, and GADA persisted throughout the follow‐up. Despite T‐cell reactivity to both GAD65 and proinsulin, autoantibodies to other islet autoantigens did not develop.

Conclusions

Further follow‐up will determine whether the beta‐cell autoimmunity observed in this patient will eventually lead to T1D. Copyright © 2010 John Wiley & Sons, Ltd.     

Candidate T cell epitopes of the human La/SSB autoantigen

OBJECTIVE: To identify T cell epitopes of the human La autoantigen involved in the generation of anti-Ro/La autoantibodies. METHODS: Molecular techniques were used for HLA typing of 219 white patients with systemic lupus erythematosus and 125 white patients with primary Sj?gren's syndrome. Anti-Ro/La antibody levels were measured by enzyme-linked immunosorbent assay. Peripheral blood mononuclear cell responses to an overlapping series of synthetic 15-mer peptides spanning the entire La sequence were examined in pools or individually in conventional 7-day proliferation assays. RESULTS: HLA typing confirmed that the HLA-DR3/DQ2 haplotype is closely associated with the occurrence of anti-Ro/La antibodies, and that the frequency of HLA-DR1 and DR4 haplotypes is reduced among antibody-positive patients. We identified 3 regions of the La sequence likely to contain T cell epitopes and 1 peptide, La 49-63, that generated a low-level but clear-cut T cell proliferative response. The HLA restrictions of these responses mirrored the HLA association data from the cohort study. Among individuals who were HLA-DR3 positive, there was no difference between patients and controls in the proliferative response to the La 49-63 peptide. CONCLUSION: Our data suggest that these are naive T cell responses, and that the identification of T cell epitopes involved in the generation of anti-Ro/La autoantibodies should focus on alternative candidate antigens.     

Increased anxiety and altered responses to anxiolytics in mice deficient in the 65-kDa isoform of glutamic acid decarboxylase

The larger isoform of the enzyme glutamate decarboxylase, GAD67, synthesizes >90% of basal levels of γ-aminobutyric acid (GABA) in the brain. In contrast, the smaller isoform, GAD65, has been implicated in the fine-tuning of inhibitory neurotransmission. Mice deficient in GAD65 exhibit increased anxiety-like responses in both the open field and elevated zero maze assays. Additionally, GAD65-deficient mice have a diminished response to the anxiolytics diazepam and pentobarbital, both of which interact with GABA-A receptors in a GABA-dependent fashion to facilitate GABAergic neurotransmission. Loss of GAD65-generated GABA does not appear to result in compensatory postsynaptic GABA-A receptor changes based on radioligand receptor binding studies, which revealed no change in the postsynaptic GABA-A receptor density. Furthermore, mutant and wild-type animals do not differ in their behavioral response to muscimol, which acts independently of the presence of GABA. We propose that stress-induced GABA release is impaired in GAD65-deficient mice, resulting in increased anxiety-like responses and a diminished response to the acute effects of drugs that facilitate the actions of released GABA.