The Germinal Center and T cell help in Three Phases of Clearance of Plasmodium

摘要 尽管感染控制有所改善，但每分钟仍有一名儿童死于疟疾，疟疾是由 被疟原虫感染。儿童在多次暴露后对疟疾的免疫力发展缓慢，并且 在没有持续接触的情况下失去免疫力。对抗体反应缺乏批判性知识 控制这种感染的方法阻碍了疫苗的开发。Th1细胞早期干扰素-γ抑制早期寄生虫生长 并与保护相关联。CD4T辅助细胞(Th)也促进寄生虫特异性抗体，我们有 建议的主要目的是彻底清除寄生虫，这需要一个多月的时间。IL-21促进B细胞增殖 这也是清除疟原虫所必需的。脾生发中心优化B：T细胞 促进抗体的同型转换和亲和力成熟的相互作用，以及长寿的浆细胞 一代。然而，由于Th1反应，GCs的出现被推迟到感染后期。这么慢 反应可能解释了在现场观察到的免疫发育延迟的原因。然而，有一个 显著的卵泡外抗体反应更快，实际上与戏剧性地控制 寄生虫。此外，我们的初步数据显示，缺乏生发中心(GC)控制的基因敲除小鼠 感染，导致我们开发了一个由三个阶段组成的保护工作模式。首先，Th1细胞因子限制 其次，GC非依赖因子将寄生虫控制在低水平，但没有病理的慢性水平； 当最终，GC在完全清除中发挥作用。然而，所需的Th细胞的类型，以及主要的 抗体介导的寄生虫杀灭机制尚不清楚，特别是在控制阶段。这个 IL-21在卵泡外反应中的作用尚未得到充分的研究，以了解其机制或 重要性。因此，我们假设IL-21驱动的GC非依赖性机制对 对控制疟原虫感染的贡献。为了测试这一点，在目标1中，我们将比较 GCS和IL-21用于控制寄生虫。我们将通过以下方式确定GC驱动的抗体变化的重要性 使用分别在同型转换和亲和力成熟方面存在缺陷的新型小鼠模型。也有 关于在疟疾感染中帮助B细胞产生抗体的Th细胞类型的重要悬而未决的问题。 我们和其他人最近发现，效应T辅助细胞对小鼠和人类疟疾的反应 主要由干扰素-γ+IL-21+Th1/Tfh混合细胞类型组成，具有Th1和Tfh的所有特征。 虽然干扰素-γ最近被证明可以抑制GC的形成，但混合干扰素-γ+/IL-21+T细胞对 体内抗体的产生，以及它们在防止疟疾寄生虫血症和病理中的作用，还没有 已经测试过了。因此，在目标2中，我们将通过以下方式评估混合干扰素-γ+/IL-21+Th1/Tfh的保护作用 使用细胞因子报告小鼠对它们进行分类，并确定IL-21关键的感染阶段。 了解控制阶段和最终清除的机制是至关重要的，因为控制 寄生虫对应于疟疾病理的终止，并可能提出新的疫苗策略。

ABSTRACT Despite improvements in infection control, one child dies every minute from malaria, which is caused by infection by Plasmodium parasites. Children develop immunity to malaria slowly after multiple exposures, and lose immunity in the absence of continuous exposure. A lack of critical knowledge about the antibody response that controls this infection hinders vaccine development. Early IFN-γ from Th1 cells limits early parasite growth and correlates with protection. CD4 T helper cells (Th) also promote parasite-specific antibody, which we have proposed is primarily required for full parasite clearance, which takes over a month. IL-21 promotes B cell responses and is also required for clearance of Plasmodium. Splenic germinal centers optimize B:T cell interactions that promote isotype switching and affinity maturation of antibodies, and long-lived plasma cell generation. However, the appearance of GCs is delayed until late in infection by the Th1 response. This slow response may explain the delay of development of immunity observed in the field. However, there is a significant extrafollicular antibody response that is faster, and actually corresponds with dramatic control of the parasite. In addition, our preliminary data showing that knockout mice lacking germinal centers (GC) control infection, led us to develop a working model of protection consisting of three phases. First, Th1 cytokines limit parasite growth; next, GC-independent factors control the parasite to low, but chronic levels without pathology; when finally, GCs play a role in complete clearance. Yet, the types of Th cells required, and the dominant mechanisms of antibody-mediated parasite killing are not yet clear, especially in the control phase. The role of IL-21 in an extrafollicular response has not been sufficiently studied to understand the mechanisms or importance. Therefore, we hypothesize that GC-independent mechanisms driven by IL-21 make a significant contribution to the control of Plasmodium infection. To test this, in Aim 1, we will compare the contribution of GCs and IL-21 for control of parasite. We will determine the importance of GC-driven antibody changes by using novel mouse models separately deficient in isotype switching and affinity maturation. There are also important unanswered questions about the type of Th cells that help B cells make antibody in malaria infection. We and others have recently discovered that the effector T helper cell response to mouse and human malaria is composed largely of a hybrid IFN-γ+ IL-21+ Th1/Tfh cell type that has all the hallmarks of both Th1 and Tfh. While IFN-γ was recently shown to inhibit GC formation, the role of hybrid IFN-γ+/IL-21+ T cells' contribution to antibody production in vivo, and their role in protection from parasitemia and pathology in malaria, have not been tested. Therefore, In Aim 2 we will evaluate the efficacy of hybrid IFN-γ+/IL-21+ Th1/Tfh in protection, by sorting them using cytokine reporter mice, and determine the phases of infection where IL-21 is critical. Understanding the mechanisms of both the control phase and final clearance is critical because control of parasite corresponds with termination of malaria pathology and may suggest novel vaccine strategies.