CD4 effector contraction in influenza

说明(申请人提供)：保护性免疫依赖于最初与病原体接触时产生的记忆CD4T细胞。幼稚的CD4T细胞对流感病毒反应强烈，通过直接在肺内推动B细胞抗体的产生，扩大并分化为大量的效应群体，间接参与流感的清除。一旦产生，CD8和CD4T效应细胞就会迁移到肺部，病毒被迅速清除，而CD4效应细胞在肺和其他地方也同样迅速收缩，在外围位置留下记忆的CD4T细胞。收缩是限制肺内CD4效应器介导的免疫病理所必需的，但调节收缩的因素尚不清楚。流感病毒在肺上皮细胞中复制，产生数十亿种病毒，导致高水平的流感抗原(Ag)呈递，并通过识别病毒RNA来戏剧性地刺激先天性免疫细胞。我们推测，这些先天事件导致炎性细胞因子的分泌，包括肿瘤坏死因子和白介素6，这些因素作用于流感特异性CD4T细胞的一小部分初始群体，以驱动复杂的反应程序，包括对效应者的广泛扩增和分化，以及当效应者在肺和外周再次遇到抗原时死亡的承诺。我们已经开发了一个模型，在这个模型中，我们可以通过将一组容易识别的流感特异性幼稚CD4T细胞从T细胞受体转基因小鼠转移到宿主小鼠中，然后我们将其感染流感，从而研究CD4收缩。这使得我们可以通过列举肺中反应最强的效应器和几天后刚刚收缩之后的效应器来可视化收缩阶段。我们将提出几个关键问题来评估我们的假设。首先，我们将询问在收缩开始时表达的流感抗原是否是通过抗原诱导的细胞死亡来诱导CD4效应器缺失的过程所必需的。第二个问题是，由于感染而产生的炎性细胞因子--肿瘤坏死因子和白介素6是否对有效的T细胞反应和收缩阶段起到了编程作用。第三，我们将询问他们是否通过增加应答的CD4T细胞产生IL-2和IL-21来完成这一编程。确定调节收缩阶段的因素应该能更好地理解保护性免疫的相关性，并建议未来操纵免疫病理学和记忆生成的目标。这些结果将有助于改进疫苗的设计，这些疫苗在对抗免疫方面更有效，但避免了免疫介导的病理后果。公共卫生相关性：感染病毒和细菌会产生强烈的T细胞免疫反应，有助于摧毁感染源，通常还会导致长期免疫，因此后续感染将得到快速有效的抗击。这种免疫力是由所谓的记忆T细胞介导的。尤其重要的是，我们要学习如何最好地产生记忆T细胞。当像流感这样的新病毒株出现时，我们拥有的另一种主要免疫，由抗体介导，不再有效，因为病毒已经改变来逃避抗体，这种逃避可能会导致危险的流行病或大流行，就像1918年导致数百万人死亡的西班牙流感，所以我们必须依靠T细胞记忆。记忆性T细胞的产生过程还不是很清楚。在反应过程中，形成了大量的T细胞效应器，在流感的情况下，其中许多进入肺部并攻击受感染的细胞。一旦病毒消失，这些“收缩”留下的记忆T细胞，主要是在淋巴器官，如脾。在这个项目中，我们将确定这种收缩过程是如何调节的，这样我们就可以学习如何设计能够实现最佳T细胞记忆的疫苗。

DESCRIPTION (provided by applicant): Protective immunity depends on memory CD4 T cells generated during initial encounter with pathogen. Naive CD4 T cells respond vigorously to influenza (Flu) virus, expanding and differentiating into a large effector population that participates in flu clearance indirectly by driving B cell antibody production and directly in the lung. Once generated, CD8 and CD4 T effector cells migrate to the lung, virus is cleared rapidly and the CD4 effector population just as quickly contracts both in the lung and elsewhere, leaving memory CD4 T cells in peripheral sites. The contraction is necessary to limit CD4 effector-mediated immunopathology in the lung, but the factors regulating contraction are as yet unknown. Flu viruses replicate in lung epithelial cells, generating billions of viruses leading to high levels of Flu antigen (Ag) presentation and as well to dramatic stimulation of the innate immune cells via recognition of viral RNA. We postulate that these innate events result in secretion of inflammatory cytokines, including TNF and IL-6, and that these factors act on the small initial population of CD4 T cells specific for Flu, to drive a complex program of response that includes both extensive expansion and differentiation to effectors as well as their commitment to die when they re-encounter Ag in the lung and periphery. We have developed a model in which we can study CD4 contraction, by transferring an easily identified "indicator" population of Flu-specific naive CD4 T cells from T cell receptor transgenic mice into a host mouse that we then infect with Flu. This allows us to visualize the contraction phase by enumerating effectors in the lung at the peak of their response and just after contraction a few days later. We will ask several key questions to evaluate our hypothesis. First we will ask if Flu Ag, expressed at the initiation of contraction, is necessary to induce the process of deletion of CD4 effectors via Ag-induced cell death. Second will ask if inflammatory cytokines, TNF and IL-6, elaborated as a result of infection, are acting to program both the effective T cell response and the contraction phase. Third we will ask if they accomplish this programming by increasing responding CD4 T cell production of IL-2 and IL-21. Identifying the factors that regulate the contraction phase should provide better understanding of the correlates of protective immunity and suggest future targets for manipulating immunopathology and memory generation. These results will help improve design of vaccines that are more effective in combating immunity but that avoid the consequences of immune-mediated pathology. PUBLIC HEALTH RELEVANCE: Infection with viruses and bacteria generate vigorous T cell immune responses that help destroy the infectious agent and also usually lead to long term immunity, so a subsequent infection will be combated swiftly and effectively. This immunity is mediated by so-called memory T cells. It is a particular importance that we learn how to best generate memory T cells. When new strains of a virus like influenza emerge, the other major kind of immunity we have, mediated by Ab, is no longer effective because the virus has changed to evade the Ab, This escape can lead to dangerous epidemics or pandemics, like the 1918 "Spanish" influenza that killed many millions, so we must depend on T cell memory. The process of memory T cell generation is not well understood. During response a very large population of T cell effectors is formed, and in the case of influenza, many of these go to the lung and attack infected cells. Once virus is gone, these "contract" leaving behind memory T cells, mostly in lymphoid organs like the spleen. In this project we will determine how this process of contraction is regulated, so that we can learn how to design vaccines that can achieve the best T cell memory.