Antigen-driven B cell development at the follicular perimeter

描述（由申请方提供）：在导致体液免疫发展的T细胞依赖性（TD）B细胞免疫应答期间，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）。过去的数据表明，在第一次接合抗原后，B细胞迁移到SLO中的T和B细胞区的边界，接受共刺激，随后迁移到T细胞区的外部区域并成为抗体形成细胞（AFC），或者迁移到B细胞滤泡的中心并使生发中心（GC）反应成核，导致长寿命AFC和记忆B细胞的发育。 最近，我们发现了TD B细胞反应中的一个先前未被认识的步骤，该步骤发生在B细胞与T细胞在T-B界面处相互作用之后，并且在脾脏中的GC反应之前。在此阶段，抗原活化的B细胞位于B细胞滤泡的周边，与T细胞区相对。在那里，它们经历快速增殖，但不经历重链类别转换或体细胞超突变，并且开始获得GC B细胞的几个特征。 更详细的机制的理解驱动B细胞的滤泡周边的因素，促进他们在这个网站的增殖，并调节他们随后迁移到其他网站在SLO将需要更高分辨率的研究这种反应。多光子活体成像（MP-IVI）技术是理想的，但其目前的应用这种类型的研究是有限的，在小鼠淋巴结（LN）的反应成像。因此，在目标1中，我们将确定毛囊周长响应是否发生在LN中。如果我们发现它是，我们将继续使用MP-IVI的真实的时间分析这个响应。如果没有，我们未来的研究将集中在这种脾脏特异性反应的生理相关性。 此外，我们以前的研究滤泡周边反应主要利用了B细胞抗原受体（BCR）转基因系统，其中，由于未知的原因，BCR驱动抗原激活的B细胞主要进入GC。由于滤泡周边反应发生在T细胞共刺激B细胞之后，该阶段可能是B细胞随后发育为短寿命AFC以及GC B细胞的先决条件.由于我们过去的模型系统不足以检验这一假设，在本提案的目标2中，我们将使用另一种BCR转基因系统，其中已知抗原活化的B细胞有效地使短寿命AFC和GC途径成核。如果我们发现滤泡周边反应先于短寿命AFC和GC的发展，未来的研究将集中在可能调节参与滤泡周边反应的B细胞对这两种分化命运之一的承诺的因素上。 公共卫生相关性：开发刺激抗体介导的免疫的更有效的疫苗需要更好地理解抗体产生B细胞如何在免疫应答期间产生并在其后维持。在这项研究中，我们将进一步表征最近发现的B细胞免疫反应阶段，我们认为这对有效的短期和长期抗体反应的发展至关重要。

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. PUBLIC HEALTH RELEVANCE: The development of more effective vaccines that stimulate antibody-mediated immunity requires a better understanding of how antibody producing B cells are generated during immune responses and maintained thereafter. In this study we will further characterize a recently discovered stage of the B cell immune response that we suggest is critical for the development of effective short and long-term antibody responses.