生发中心在体液免疫应答中起到至关重要的作用。活化B细胞在生发中心快速增殖并不断进行体细胞高频突变，以便在与其他B细胞竞争过程中获取尽可能多的抗原。B细胞通过呈递获得的抗原与滤泡辅助性T细胞相互作用以获得存活信号。通过滤泡辅助性T细胞对B细胞筛选，使得优质的B细胞存活并不断壮大自己的后代数目，最终有效输出分泌高亲和力抗体的浆细胞以及能够快速响应抗原的记忆性B细胞。滤泡辅助性T细胞和生发中心B细胞的相互作用作为生发中心发育的关键监督限制步骤，需要受到从分子水平到细胞水平上的多层次调控，以使生发中心更加有效地行使体液免疫的功能。ICOSL-ICOS能够调节T-B细胞互作的紧密程度并且促进滤泡辅助性T细胞上调CD40L，但是这一过程实现的分子机制并不是完全清楚。通过在体双光子成像以及胞内钙信号报告基因对滤泡辅助性T细胞接受的TCR信号进行实时监测，发现ICOSL-ICOS在分子水平上调节TCR下游信号的强度同时又增强了二者相互作用的接触强度，从而调控了T-B细胞的互作效率以及T细胞和B细胞上调相关共刺激分子。除了从分子水平对T-B互作的影响，之前工作发现EFNB1分子在生发中心B细胞上高表达，可以调控滤泡辅助性T细胞迁移到生发中心的数目。然而EFNB1如何通过影响T-B互作而影响细胞数目的仍不得而知，通过活体双光子对T-B互作过程的细致观察，发现B细胞表面的EFNB1分子可以和其在滤泡辅助性T细胞上表达的受体EPHB6相互作用，在T-B互作中对滤泡辅助性T细胞进行排斥，从而控制了迁移到生发中心的细胞总数，在细胞群体水平上对T-B细胞互作进行了调控。再者根据之前的研究，我们发现在T-B细胞互作过程中，B细胞的形状和大小也会影响互作的有效程度。因此对生发中心B细胞进行形状的控制是至关重要的。然而，相关的机制目前还不是特别清楚。我们发现激动蛋白解聚分子destrin通过调节F-actin的动态来调节生发中心B细胞的形态。Destrin不但可以调控B细胞在生发中心的运动状态，还可以调节T-B细胞互作过程内二者接触面积的有效程度，从而调控生发中心的发育以及输出浆细胞所分泌抗体的亲和力。通过destrin对B细胞在单细胞水平的微调，使得整个生发中心反应能够有效的进行。综合以上三方面所述，本文主要对生发中心反应中T-B细胞互作和细胞的动态学进行探索，从分子水平、细胞群体水平以及单细胞水平对T-B细胞互作进行了阐述和解读，从而对生发中心的分化发育进行了研究。
Germinal center plays a pivotal role in humoral immunity as a micro-anatomical structure, which is responsible for high-affinity antibody production and memory B cell formation. Cognate B cells get activated and migrate into germinal center during antigen invasion to undergo proliferation and somatic hypermutation. T follicular helper cells deliver survival signal to B cells according to the amount of antigen that they perceive on B cells, which is able to select the most competent B cells leading to germinal center clonal selection and affinity maturation.As censors for germinal center B cell selection, T follicular helper cells contact with B cells in a transient and highly dynamic way, which is supposed to be regulated stringently. According to the previous data documented, ICOSL-ICOS interaction is very important to regulate T cell entanglement to B cells, so as to regulate CD40L delivery from T cells. However, it is unclear how ICOSL-ICOS interaction affects T-B contact and co-stimulation signal delivery. With the help of intravital imaging and genetically encoded calcium indicator, ICOSL-ICOS interaction can not only change T-B contact efficiency but also enhance TCR signal so as to promote CD40L delivery and regulate germinal center selction.In addition to molecular regulation of T-B contact such as ICOSL-ICOS, previous we found EFNB1 is highly expressed on germinal center B cells to control T follicular helper cells amount within germinal center. But it is elusive how B cells regulate the milieu to control T cells entry of germinal center. Via intravital imaging, we observe that EFNB1-EPHB6 interaction endows T-B contact with repulsive effects preventing T cells from migrating into germinal center too much. Therefore, the prepulsive effect of EFNB1 control the amount of survival signal from T follicular helper cells in a way of limiting cell number. Furthermore, it is known that T-B contact is also regulated by the shape of germinal center B cells and so that the B cell shape is supposed to be controlled during T-B contact. Here we uncover that destrin, the actin depolymerizing factor, is highly expressed on germinal center B cells, and is able to regulate B cell morphology, so that migration ability and T-B contact are regulated, leading to germinal center undergoing better clonal selection and affinity maturation, which is supposed to enhance high-affinity plasma cell production.To summary, we focus on cell migration and T-B cell contact in germinal center and depict affinity maturation of germinal center in different views.
