WASP缺陷促进T-bet高表达非典型记忆B细胞分化的机制研究

Atypical memory B cells (aMBCs) was considered as an exhausted subset of memory B cells with high expression of T-bet. However, the differentiation mechanism of the aMBCs remains unknown. It has been reported that interferons gamma(IFNγ) driving T-bet "overexpression" may play a role in aMBC differentiation. Our previous study have found that WAS patients with a significantly increase in T-bet hi aMBCs, which may be one of the reasons for the immune deficiency in WAS. Then, We found IFNγ secreted by activated CD4+T cells was increased in WAS patients and WASKO mice, and the number of aMBCs was significantly increased with IFNγ stimulation in WAS patients. So we hypothesized that WASP defects leads to excessive IFNγ repeated stimulation, which induce T-bet expression in B cells and inhibit BCR signaling, that drive naïve B cells differentiate into aMBCs instead of entering germinal center. This study is focus on the function and differentiation mechanism of aMBCs. The results may remind new mechanism of immune deficiency in WAS, it will also provide new clues for precise treatment of WAS patients and the design of the vaccine.

非典型记忆B细胞(aMBCs)被认为是一类耗竭状态的记忆B细胞亚群，具有高表达T-bet及其他表型特征，其分化机制尚不清楚。既往研究提示IFNγ诱导T-bet过度表达可能是调控aMBCs分化的重要机制。WAS患儿有体液免疫缺陷，我们前期发现WAS患儿T-bet高表达aMBCs增多，WAS患儿及WASKO小鼠CD4+T细胞激活后分泌IFNγ增多，且WAS患儿B细胞经IFNγ刺激后，aMBCs数量增加。故我们提出假设，WASP缺陷导致IFNγ过多分泌，反复刺激诱导B细胞T-bet表达，使其BCR抑制信号增强，不能进入生发中心而形成大量aMBCs。本研究拟首先验证WAS患儿aMBCs功能，进一步解析WASP通过BCR相关负性调控影响aMBCs分化机制，阐明aMBCs形成对体液免疫的影响。本研究属原创性研究，可为WAS体液免疫缺陷提供新机制，更可为相关疾病的精准防治和优化疫苗设计提供部分理论基础。

WAS综合征以幼年出现湿疹、血小板减少，反复感染为特征，且易患自身免疫性疾病和肿瘤，既往研究证实WAS患者体液免疫缺陷。非典型记忆B细胞（Atypical memory B cells, aMBCs）是近几年新发现的B细胞亚群，主要存在于慢性感染性疾病和自身免疫性疾病患者中，aMBCs与经典记忆B细胞（classical memory B cells, cMBCs）具有相近的体细胞超突变频率，经历了相似程度的细胞分化和克隆扩增，但其细胞表面的BCR对抗原刺激不产生有效反应，其功能及在体液免疫中的作用尚未完全明确。我们前期研究发现WAS患者的外周血中aMBCs较同龄健康儿童明显增多，且aMBCs在外周血中比例与WAS评分呈正相关，提示aMBCs升高与WAS病人的感染、自身免疫表现相关。但aMBCs在WAS患者体液免疫中发挥的作用仍未知。我们通过比较WAS患者aMBCs与cMBCs功能水平，证实WAS患者aMBCs较cMBCs功能受抑制，包括增殖减弱、凋亡增强，BCR磷酸化水平减弱。而WAS病人aMBCs增多的原因可能是WASp缺陷导致T细胞过多分泌IFN-γ，使血浆中IFN-γ水平明显增高，同时aMBCs的BCR磷酸化水平较正常对照增强，且血浆中增高的BAFF进一步促进了aMBCs的存活。但aMBCs的体液免疫功能还需进一步解析。本课题研究结果将进一步阐明WASp缺陷对体液免疫的影响，亦将助于进一步解析WASp这一结构复杂蛋白质的功能。