Role of Structural Flexibility in the Selection of Immunodominant MHCII Epitopes

结构灵活性在免疫显性 MHCII 表位选择中的作用

• 批准号: 9107291
• 负责人: Andrea Ferrante
• 金额: $ 32.96万
• 依托单位: UNIVERSITY OF ALASKA FAIRBANKS
• 依托单位国家: 美国
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-03-01 至 2021-02-28
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9107291
• 关键词: Address; Adopted; Affinity; Alleles; Anisotropy; Antigen Presentation; Antigen Presentation Pathway; Antigen-Presenting Cells; Antigens; Area; Binding; CD4 Positive T Lymphocytes; Calorimetry; Cathepsins; Complex; DR1 gene; Elements; Epitopes; Event; Free Energy; Gel; Generations; Genetic Polymorphism; Goals; HLA-DR Antigens; HLA-DR1 Antigen; Histocompatibility Antigens Class II; Human; Immune; Immunodominant Epitopes; Incubated; Influenza A Virus, H1N1 Subtype; Investigation; Kinetics; Lead; Major Histocompatibility Complex; Mass Spectrum Analysis; Measures; Modeling; Nature; Peptide Library; Peptides; Play; Predisposition; Probability; Process; Property; Proteins; Proteolysis; Reaction; Role; Sequence Analysis; Side; Social Dominance; Staging; Structure; Surface; System; T cell response; T memory cell; T-Cell Receptor; T-Lymphocyte; Testing; Thermodynamics; Transplantation; Vaccination; Vaccine Design; adaptive immunity; base; flexibility; grasp; immune function; insight; prevent; public health relevance; response; vaccine development

 DESCRIPTION (provided by applicant): The adaptive immune response starts when CD4+ T cells recognize antigenic peptides presented by class II molecules of the Major Histocompatibility Complex (MHCII). In general, this response focuses on very few representative peptides from each possible pathogenic agent, referred to as immunodominant epitopes. Though immunodominance has been observed for several years, the underlying mechanisms are still unclear. Two outstanding features of MHCII molecules complicate our ability to understand immunodominance: their extensive polymorphism and the ability of each allele to bind large panoply of peptides. A third confounding factor is that epitope selection usually takes place in the presence of HLA-DM (DM), of which activity, not fully elucidated, results in the generation of an antigenic repertoire skewed toward kinetically and energetically stable peptide-MHCII complexes (pMHCII). Our long-term goal is to formally describe the stages of the epitope selection and recognition process. A better grasp on the mechanisms involved in the generation of dominant epitopes and T cell responses to them is important in areas where MHCII plays a significant role, such as vaccination and transplantation. This proposal addresses immunodominance at the level of the peptide and the MHC. We have been investigating the pMHCII interaction with a different approach than the typical kinetic analysis, by looking at the thermodynamic aspects of complex formation. We have shown for the human MHCII HLA-DR1 (DR1) that different peptides can bind with comparable affinities adopting different thermodynamic mechanisms. In addition, we have shown that complexes, of which formation requires smaller entropic penalty, feature greater conformational flexibility and are more susceptible to DM action. Our observations lead us hypothesize that a correlation exists between: 1) peptide binding thermodynamics, 2) pMHCII structure and conformational flexibility and 3) DM-susceptibility. Moreover, we hypothesize that binding and DM-susceptibility may alternatively control or being controlled by the availability of candidate epitopes as defined by endosomal proteolysis, and together these three processes determine the selection of immunodominant epitopes. To test these hypotheses, in Aim 1 we will consider a library of peptides derived from HA H1N1 for which DR1- restricted dominance hierarchy has been established, and we will analyze binding and kinetic properties of these peptides in complex with DR1. Moreover, for a subset of sequences, we will probe the correlation between thermodynamics of binding, structural flexibility of the respective complexes and DM-susceptibility. In Aim 2 we will incubate, together or in sequence, the whole H1 protein with cathepsins, DR1 and DM, we will probe the kinetics of reaction in 2D gels and we will use mass spectrometry (MS) to analyze sequences eluted from DR1 at the end of each incubation. We will compare the H1 epitope hierarchy with the MS-identified sequences to determine the relative role of proteolysis and DM-susceptibility in the generation of dominance.

 描述（由申请方提供）：当CD 4 + T细胞识别主要组织相容性复合物（MHCII）II类分子呈递的抗原肽时，适应性免疫应答开始。一般来说，这种反应集中在来自每种可能的病原体的非常少的代表性肽，称为免疫显性表位。虽然免疫优势已经观察了几年，但其潜在机制仍不清楚。MHCII分子的两个突出特征使我们理解免疫优势的能力变得复杂：它们广泛的多态性和每个等位基因结合大量肽的能力。第三个混杂因素是表位选择通常在HLA-DM（DM）存在下发生，其活性未完全阐明，导致产生偏向于动力学和能量稳定的肽-MHCII复合物（pMHCII）的抗原库。我们的长期目标是正式描述表位选择和识别过程的各个阶段。更好地掌握参与优势表位产生和T细胞对它们的反应的机制在MHCII发挥重要作用的领域（如疫苗接种和移植）非常重要。这一建议解决了肽和MHC水平上的免疫优势。我们一直在研究的pMHCII相互作用与一个不同的方法比典型的动力学分析，通过看复杂的形成的热力学方面。我们已经表明，对于人MHCII HLA-DR 1（DR 1），不同的肽可以采用不同的热力学机制以相当的亲和力结合。此外，我们已经表明，复合物的形成需要较小的熵罚，具有更大的构象灵活性，更容易受到DM行动。我们的观察使我们假设：1）肽结合热力学，2）pMHCII结构和构象灵活性和3）DM易感性之间存在相关性。此外，我们假设，结合和DM易感性可能会交替控制或被控制的候选表位的可用性所定义的内体蛋白水解，这三个过程一起决定了免疫显性表位的选择。为了验证这些假设，在目标1中，我们将考虑来自HA H1N1的肽库，其中已经建立了DR 1限制性优势等级，并且我们将分析这些肽与DR 1复合的结合和动力学性质。此外，对于一个子集的序列，我们将探讨热力学的结合，各自的复合物和DM敏感性的结构灵活性之间的相关性。在目标2中，我们将与组织蛋白酶、DR 1和DM一起或按顺序孵育整个H1蛋白，我们将探测2D凝胶中的反应动力学，我们将使用质谱（MS）分析每次孵育结束时从DR 1洗脱的序列。我们将比较H1表位层次与MS鉴定的序列，以确定蛋白水解和DM易感性在优势产生中的相对作用。