Class II Processing and Presentation During Secondary Responses to Influenza

描述（由申请人提供）：初始CD4+ T细胞（TCD4+）的激活是由MHCII类（MHCII）结合肽（表位）驱动的，这些肽显示在树突状细胞（dc）表面，这些树突状细胞（dc）从感染部位转运到区域淋巴结。虽然大多数研究都集中在主要反应上，但自然界中的大多数病原体暴露都是在完全不同的环境中重复发生的。事实上，我们假设记忆TCD4+的激活，越来越被认为是回忆反应的一个关键方面，从根本上是不同的。这在很大程度上归因于抗原特异性B细胞的存在，它们具有独特的抗原处理能力。因此，这推动了TCD4+特异性的重大转变，这些特异性来自于回忆与原发性反应。通过完善的流感模型发挥这两个共同项目的经验，这一假设将通过两个紧密相连的具体目标来实现。在第一个目标中，B细胞在二次应答中的影响将通过以下方式进行评估：a)在二次攻击之前选择性地消除或打开记忆B细胞上的MHCII； B)通过含有选择性miRNA靶向序列的工程病毒将流感蛋白表达限制在特定细胞类型。在第二个目标中，将通过体外TCD4+激活试验评估体外流感特异性B细胞相对于dc的抗原加工和提呈能力。预测这些抗原呈递细胞（APC）类型之间观察到的差异将为TCD4+特异性提供基础，这些特异性在继发性反应和原发性反应期间被放大。该项目预计将为探索促进B细胞介导的呈递的加工机制、记忆B细胞在对其他病原体的反应中的作用以及利用所得到的原则加强合理疫苗设计的更多应用研究奠定基础。

DESCRIPTION (provided by applicant): Activation of naive CD4+ T cells (TCD4+) is driven by MHC class II (MHCII)-bound peptides (epitopes) displayed at the surfaces of dendritic cells (DCs) that have trafficked from sites of infection to regional lymph nodes. While most studies concentrate on the primary response, the majority of pathogen exposures in nature are repeat encounters that play out in decidedly different contexts. Indeed, we hypothesize that activation of memory TCD4+, increasingly appreciated as a key aspect of the recall response, is fundamentally distinct. This is attributable in large part to the presence of antigen-specific B cells, which possess unique antigen processing capabilities. Consequently, this drives a significant shift in the TCD4+ specificities that emerge from recall vs. primary responses. Through well-established influenza models that play to the experience of both co-PIs, this hypothesis will be pursued via two tightly linked specific aims. In the first aim the impact of B cells in the secondary response will be assessed by: a) selectively eliminating or turning on MHCII on memory B cells prior to a secondary challenge, and b) restricting flu protein expression to specific cell types by engineering viruses that contain selective miRNA targeting sequences. In the second aim the antigen processing and presenting capabilities of ex vivo flu-specific B cells vs. DCs will be assessed by in vitro TCD4+ activation assays. The prediction is that the observed differences between these antigen presenting cell (APC) types will provide a basis for the TCD4+ specificities that are amplified during the secondary vs. primary responses. This project is expected to set the stage for studies that explore the processing machinery that facilitates B cell-mediated presentation, the role of memory B cells in responses to other pathogens, as well as more applied studies that leverage resulting principles to enhance rational vaccine design.