Molecular Mechanisms Linking HLA-DQ and Autoimmunity

描述(申请人提供)：胰岛素依赖型糖尿病(IDDM)和乳糜泻是人类最常见的两种免疫介导性疾病。为了开发治疗这两种疾病的新方法，我们决定研究它们与相同的主要组织相容性复合体(MHC)II类分子--人类白细胞抗原-DQ8之间的联系机制。这些分子与HLADQ2、HLADR0405和I-Ag7共享其链57位的突变，该突变消除了保守的天冬氨酸，并改变了P9囊的电荷和形状。我们已经评估了当结合的多肽在第9位没有天冬氨酸/谷氨酸残基时，这种突变在小鼠和人类中的功能后果(P9)。在所有情况下，这种情况都会导致T细胞受体(TCR)的CDR3中Asp/Glu残基的选择。CDR3上的Asp/Glu与非Asp/Glu P9多肽配对，显著增加了TCR/pMHC的亲和力，支持T细胞的扩增。对I-Ag7/T细胞受体复合体一级结构的测定，结合生物物理测量，表明这一现象是由非TCR接触残基通过静电力在一段距离内诱导的。在目前的提案中，我们建议进一步探讨仅与肽的P9残基的性质有关的低TCR亲和力和高TCR亲和力之间的转换(“P9开关模型”)在疾病发生和发展中可能起到的作用。为了探索这一迷人的可能性，我们提出了三个具体目标。目的1：评价MHC 57位在T细胞谱系选择中的作用。我们推测，当P9的多肽不携带天冬氨酸/谷氨酸时，MHC的57位直接选择亲和力较高的T细胞。对于已经显示的外源抗原，如醇溶蛋白和溶菌酶，我们将在I-Ag7和HL A-DQ8的背景下评估这种识别自身抗原的模式，如BDC2.5、GAD65和胰岛素。目的2：支持57位基因在T细胞受体相互作用中的作用机制。我们将结合生物物理和结构研究来了解当TCR在其CDR3中保留Asp/Glu残基时，在I-Ag7或HL A-DQ8的背景下识别在P9具有中性残基的多肽时所发生的亲和力增加。目的3：通过动物模型验证P9开关模型在自身免疫反应中的相关性。我们有间接证据表明，T细胞对某些抗原的识别取决于MHC的57和相关多肽的性质。然而，我们现在必须提供这种独特的识别模式与体内自身反应性T细胞的扩张之间的直接联系，并展示它们在疾病中的作用。我们将通过对携带I-Ag7(NOD，C57BL6.g7)的小鼠进行T细胞和逆转录基因转移研究来直接解决这个问题。此外，对突变的I-Ag757D突变小鼠的研究将直接挑战我们的模型。我们认为，我们已经确定了I-Ag7/HLA-DQ8与T细胞识别之间的独特的分子联系，并假设这种联系支持在HLA-DQ8相关疾病中自身反应性T细胞的扩张。这关系到将MHC分子重新定义为治疗的直接靶点的可能性，以及开发与HLA-DQ分子结合以改变其功能的小分子或抗体。 公共卫生相关性：胰岛素依赖型糖尿病(IDDM)和乳糜泻是人类最常见的两种自身免疫性疾病。为了开发新的治疗方法，我们正试图了解它们与MHC II类分子(如人类白细胞抗原DQ8)的关联机制，并提出有史以来第一个全面的模型进行测试。

DESCRIPTION (provided by applicant): Insulin-dependent diabetes mellitus (IDDM) and celiac disease are two of the most common immune-mediated diseases in humans. In order to develop new treatment for both conditions, we have decided to study the mechanisms underlying their association to the same Major Histocompatibility Complex (MHC) class II molecules, HLA-DQ8. These molecules share with HLA-DQ2, HLA-DR0405 and I-Ag7 a mutation at position 57 of their chain that eliminates a conserved aspartic acid and modifies the charge and shape of the P9 pocket. We have evaluated the functional consequences of this mutation in mouse and human when the bound peptide has no Asp/Glu residue at position 9 (P9). In all instances, this situation leads to the selection of Asp/Glu residues in CDR3 of T cell receptor (TCR). The pairing Asp/Glu in CDR3 with non-Asp/Glu P9 peptide increases TCR/pMHC affinity dramatically and supports T cell expansion. The determination of the first structure of an I-Ag7/T cell receptor complex, coupled with biophysical measurements, revealed that this phenomenon was induced at a distance by non-TCR contact residues through electrostatic forces. In the current proposal we propose to explore further the role that the shift between low and high TCR affinity, related solely on the nature of the P9 residue of the peptide ("the P9 switch Model"), may have in disease onset and development. To explore this fascinating possibility, we propose 3 specific aims. Aim 1: Evaluation of the role of position 57 of MHC in T cell repertoire selection. We hypothesize that position 57 of MHC directly select T cells of higher affinity when peptides do not carry Asp/Glu at P9. Already shown for exogenous antigens such as gliadin and lysozyme, we will evaluate this mode of recognition for self-antigens such as BDC2.5, GAD65 and insulin in the context of I-Ag7 and HLA-DQ8. Aim 2: Mechanisms supporting the role of position 57 in T cell receptor interactions. We will combine biophysical and structural studies to understand the gain in affinity that occurs when a TCR retaining a Asp/Glu residue in its CDR3 recognizes a peptide with a neutral residue at P9 in the context of I-Ag7 or HLA-DQ8. Aim 3: Using animal models to test the pertinence of the P9 switch model in autoimmune responses. We have circumstantial evidence showing that the T cell recognition of some antigens hinges on the nature of 57 of MHC and the associated peptide. However, we now have to provide a direct link between this unique mode of recognition and the expansion of autoreactive T cells in vivo and show their role in disease. We will address the issue directly by T cell and retrogenic transfer studies in mice carrying I-Ag7 (NOD, C57BL6.g7). In addition, studies in a mutant I-Ag757D mutant mouse will challenge directly our model. We believe that we have identified a unique molecular link between I-Ag7/HLA-DQ8 and T cell recognition and hypothesize that this link supports the expansion of autoreactive T cells in HLA-DQ8- associated diseases. At stake is the possibility to redefine MHC molecules as direct targets for treatment and the development of small molecules or antibodies binding to HLA-DQ molecules to modify their function. PUBLIC HEALTH RELEVANCE: Insulin-dependent diabetes mellitus (IDDM) and celiac disease are two of the most common autoimmune diseases in humans. To develop new therapeutic approaches we are trying to understand the mechanisms of their association with MHC class II molecules such as HLA-DQ8 and propose the first comprehensive model ever to be tested.