Intestinal Mucosal Immunity

描述（由申请方提供）：许多急性病毒感染诱导早期T细胞非依赖性多克隆B细胞活化，并在经典T细胞依赖性B生殖中心形成之前产生抗原特异性伊加或IgG。然而，启动早期T细胞非依赖性类别转换重组（CSR）的必要信号尚不清楚。本申请的目的是确定驱动T细胞非依赖性B细胞活化和伊加CSR的基本途径。我们提出利用轮状病毒感染的鼠模型，其中在病毒暴露后48小时内诱导派伊尔集合淋巴结（PP）T细胞非依赖性多克隆B细胞活化，随后产生轮状病毒特异性伊加。轮状病毒体外诱导B细胞活化需要树突状细胞。轮状病毒抗原存在于体内PP树突状细胞中，并且这些细胞在B细胞活化发生时被活化，表明树突状细胞是B细胞对轮状病毒应答的重要调节剂。我们发现B细胞活化依赖于轮状病毒颗粒的结构完整性，这表明轮状病毒诱导树突状细胞应答是模式识别的结果。初步实验表明，MyD 88表达的缺乏导致B细胞活化的消除和肠伊加水平的显著降低。我们发现B细胞活化因子（BAFF）信号通路中的突变也导致B细胞活化的消融，表明MyD 88和BAFF之间的潜在联系。PP B细胞活化后数天，PP中TGF-2表达和伊加+ B细胞数量增加，表明TGF-2在PP对轮状病毒的多克隆应答中也起重要作用。因此，我们假设树突状细胞通过诱导多克隆B细胞应答来调节PP中快速T细胞非依赖性病原体特异性抗体的产生，所述多克隆B细胞应答由MyD 88、BAFF和TGF-2信号传导引起，而不依赖于抗原特异性BCR。我们将通过使用体外和体内方法来测试这一假设，以实现以下三个目标：目标1。确定轮状病毒是否诱导树突状细胞MyD 88信号传导，从而驱动B细胞应答。目标2.确定MyD 88信号传导是否导致BAFF和TGF-β产生。目标3.描述多克隆B细胞对轮状病毒的反应。本申请中提出的研究对于解决关于肠中T细胞非依赖性抗体诱导的分子机制的未回答的问题具有重要意义。这项工作将为肠道免疫反应提供新的见解，并有助于改进粘膜疫苗策略。确定病原体如何诱导快速但特异性的抗体，对于确定早期抗体在限制病毒复制和传播以及提供保护方面的作用具有巨大的潜力。公共卫生相关性：该提案旨在了解肠道抗体对病毒病原体的反应如何由宿主启动和调节。具体而言，将研究诱导B细胞产生病毒特异性抗体所需的树突细胞和B细胞之间的最早信号。所获得的信息将通过定义新的信号通路提供对肠道免疫调节的更全面的理解，并且将与治疗剂和粘膜疫苗的开发相关。

DESCRIPTION (provided by applicant): Many acute viral infections induce early T cell independent polyclonal B cell activation and production of antigen-specific IgA or IgG prior to the formation of classical T cell dependent B germinal centers. However, the necessary signals for initiation of early T cell independent class switch recombination (CSR) are not known. The objective of this application is to determine the essential pathways that drive T cell independent B cell activation and IgA CSR. We propose to utilize the murine model of rotavirus infection in which Peyer's patch (PP) T cell independent polyclonal B cell activation is induced within 48 hours after viral exposure followed by production of rotavirus- specific IgA. Rotavirus induced B cell activation in vitro requires dendritic cells. Rotavirus antigen is present in PP dendritic cells in vivo and these cells are activated at the time B cell activation occurs, suggesting that dendritic cells are important modulators of the B cell response to rotavirus. Our finding that B cell activation is dependent on the structural integrity of the rotavirus particles suggested the possibility that rotavirus induces dendritic cell responses as a result of pattern recognition. Preliminary experiments demonstrate that lack of MyD88 expression results in an ablation of B cell activation and substantial reduction in intestinal IgA levels. We find that a mutation in the B cell activating factor (BAFF) signaling pathway also results in the ablation of B cell activation, suggesting a potential link between MyD88 and BAFF. Several days following PP B cell activation there is an increase of TGF-2 expression and numbers of IgA+ B cells in the PP, suggesting TGF-2 also plays an important role in the PP polyclonal response to rotavirus. Therefore, we hypothesize that dendritic cells modulate the production of rapid T cell independent pathogen-specific antibody in the PP through induction of a polyclonal B cell response that results from MyD88, BAFF, and TGF-2 signaling independent of an antigen-specific BCR. We will test this hypothesis by using both in vitro and in vivo approaches to pursue the following three aims: Aim 1. Determine whether rotavirus induces dendritic cell MyD88 signaling that drives B cell responses. Aim 2. Determine whether MyD88 signaling results in BAFF and TGF-ss production. Aim 3. Characterize the polyclonal B cell responses to rotavirus. The studies proposed in this application are of importance in addressing unanswered questions regarding the molecular mechanisms of T cell independent antibody induction in the intestine. This work will provide new insights into intestinal immune responses as well as contribute to improved mucosal vaccine strategies. Defining how pathogens induce rapid but specific antibody has tremendous potential to define the role of early antibody in limiting viral replication and dissemination and providing protection. PUBLIC HEALTH RELEVANCE: This proposal aims to understand how the intestinal antibody response to a viral pathogen is initiated and regulated by the host. Specifically, the earliest signals between dendritic cells and B cells required to induce B cells to produce viral specific antibodies will be investigated. Information gained will provide a more comprehensive understanding of intestinal immune regulation by defining novel signaling pathways and will be pertinent to development of therapeutics and mucosal vaccines.