Antigen-driven B cell development at the follicular perimeter

描述(由申请人提供)：在T细胞依赖(TD)B细胞免疫反应导致体液免疫发展的过程中，B细胞经历一系列有序的迁移和分化步骤。这些过程发生在次级淋巴器官(SLO)。以往的研究表明，B细胞在第一次结合抗原后，在SLO中迁移到T和B细胞区的边界，接受共刺激，随后要么迁移到T细胞区的外部成为抗体形成细胞(AFCs)，要么迁移到B细胞滤泡的中心并使生发中心(GC)反应成核，从而导致长期存活的AFCs和记忆性B细胞的发育。最近，我们在T-B界面处的B细胞与T细胞相互作用之后，在脾的GC反应之前，发现了TD B细胞反应中一个以前未被认识到的步骤。在这个阶段，抗原激活的B细胞位于B细胞滤泡的周长，与T细胞区相对。在那里，它们经历了快速的增殖，但没有重链类转换或体细胞过度突变，并开始获得GC B细胞的几个特征。要更详细地了解促使B细胞进入卵泡周缘的因素，促进B细胞在这个部位的增殖，并调节它们随后在SLO中向其他部位的迁移，将需要对这种反应进行更高分辨率的研究。多光子活体成像技术(MP-IVI)是实现这一目的的理想技术，但目前它在这类研究中的应用仅限于对小鼠淋巴结(LNS)的反应进行成像。因此，在目标1中，我们将确定LNS是否发生卵泡周长反应。如果我们发现确实如此，我们将使用MP-IVI对这一反应进行实时分析。如果没有，我们未来的研究将集中在这种脾特异性反应的生理相关性上。此外，我们以前对卵泡周长反应的研究主要是利用B细胞抗原受体(BCR)转基因系统，在这种系统中，由于未知的原因，BCR主要驱动抗原激活的B细胞进入GC。由于卵泡周长反应是在T细胞共刺激B细胞之后发生的，这一阶段可能是B细胞随后发育为短期AFC和GC B细胞的先决条件。由于我们过去的模型系统不足以验证这一假说，在本建议的目标2中，我们将使用另一种BCR转基因系统，在该系统中，已知抗原激活的B细胞可以有效地核化短暂的AFC和GC途径。如果我们发现卵泡周长反应先于短期AFC和GCs的发展，未来的研究将集中在可能调节参与卵泡周长反应的B细胞对这两种分化命运之一的承诺的因素。

DESCRIPTION (provided by applicant): During T cell dependent (TD) B cell immune responses leading to the development of humoral immunity, B cells undergo an ordered series of migratory and differentiation steps. These processes take place in secondary lymphoid organs (SLOs). Past data suggested that after first engaging antigen, B cells migrate to the border of T and B cells zones in SLOs, receive costimulation, and subsequently either migrate to the outer regions of T cell zones and become antibody forming cells (AFCs) or travel to the center of B cell follicles and nucleate the germinal center (GC) reaction, leading to development of long lived AFCs and memory B cells. Recently, we discovered a previously unrecognized step in TD B cell responses that takes place subsequent to B cell interaction with T cells at the T-B interface, and prior to the GC response in the spleen. During this stage, antigen-activated B cells are located at the perimeter of B cell follicles, opposite the T cell zone. There, they undergo rapid proliferation, but not heavy chain class switching or somatic hypermutation, and begin to acquire several characteristics of GC B cells. A more detailed mechanistic understand of the factors that drive B cells to the follicular perimeter, promote their proliferation at this ite, and regulate their subsequent migration to other sites in SLOs will require higher resolution studies of this response. The technique of multi-photon intravital imaging (MP-IVI) is ideal for this purpose but its current application for studies of this type is limited to imaging of response in mouse lymph nodes (LNs). As such, in Aim 1 we will determine if the follicular perimeter response takes place in LNs. If we find that it does, we will proceed to the real time analysis of this response using MP-IVI. If it does not, our future studies will focus on the physiological relevance of this spleen-specific response. In addition, our previous studies of the follicular perimeter response largely utilized a B cell antigen receptor (BCR) transgenic system in which, for unknown reasons, the BCR drives antigen activated B cells predominantly to enter GCs. Since the follicular perimeter response takes place subsequent to B cell costimulation by T cells, this stage may be a prerequisite for subsequent development of B cells to both short- lived AFCs, as well as GC B cells. Since our past model system was inadequate to test this hypothesis, in Aim 2 of this proposal we will using another BCR transgenic system in which antigen activated B cells are known to efficiently nucleate both short lived AFC and GC pathways. If we find that the follicular perimeter response precedes both the development of short-lived AFC and GCs, future studies will focus on the factors that may regulate the commitment of B cells participating in the follicular perimeter response to one of these two differentiative fates.