Molecular Mechanisms Linking HLA-DQ and Autoimmunity

描述（由申请人提供）：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。为了开发针对这两种疾病的新治疗方法，我们决定研究它们与主要组织相容性复合体（MHC） II类分子HLA-DQ8相关的机制。这些分子与HLA-DQ2， HLA-DR0405和I-Ag7在其链的第57位有一个突变，该突变消除了一个保守的天门氨酸，并改变了P9口袋的电荷和形状。当结合的肽在9号位置（P9）没有Asp/Glu残基时，我们已经在小鼠和人类中评估了这种突变的功能后果。在所有情况下，这种情况都会导致T细胞受体（TCR） CDR3中Asp/Glu残基的选择。CDR3中的Asp/Glu与非Asp/Glu P9肽配对，显著增加TCR/pMHC亲和力，支持T细胞扩增。I-Ag7/T细胞受体复合物的第一个结构的测定，加上生物物理测量，揭示了这种现象是由非tcr接触残留物通过静电力在远处诱导的。在目前的提案中，我们建议进一步探索低和高TCR亲和力之间的转变，仅与肽的P9残基的性质有关（“P9开关模型”），可能在疾病的发生和发展中发挥作用。为了探索这种迷人的可能性，我们提出了3个具体目标。目的1：评价MHC 57位点在T细胞库选择中的作用。我们假设当肽不携带Asp/Glu在P9时，MHC的57位直接选择亲和力更高的T细胞。我们已经对麦胶蛋白和溶菌酶等外源性抗原进行了识别，我们将在I-Ag7和HLA-DQ8的背景下评估这种对自身抗原（如BDC2.5、GAD65和胰岛素）的识别模式。目的2：支持57位在T细胞受体相互作用中的作用的机制。我们将结合生物物理和结构研究来了解当在其CDR3中保留Asp/Glu残基的TCR识别在I-Ag7或HLA-DQ8中P9处具有中性残基的肽时发生的亲和力增益。目的3：利用动物模型测试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细胞扩张之间的直接联系，并显示它们在疾病中的作用。我们将通过携带I-Ag7的小鼠的T细胞和逆转录转移研究直接解决这个问题（NOD, C57BL6.g7）。此外，在I-Ag757D突变小鼠中的研究将直接挑战我们的模型。我们相信我们已经确定了I-Ag7/HLA-DQ8与T细胞识别之间的独特分子联系，并假设这种联系支持HLA-DQ8相关疾病中自身反应性T细胞的扩增。将MHC分子重新定义为治疗的直接靶标，以及开发与HLA-DQ分子结合以改变其功能的小分子或抗体的可能性是至关重要的。

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.