抗原特异性TFH（Th21）应答及其免疫作用机制的研究

Follicular T helper (TFH) cell is considered an independent T cell subset with the defining feature of IL-21 production. TFH cells play essential role in the of help B cells to generate high affinity antibodies and in the generation of germinal centre. Our previous study indicated that Mycobacterium tuberculosis (MTB)- specific antigens could induce the production of IL-21 by CD4+ T cells from patients with tuberculous pleurisy. In addition, IL-21 could enhance the production of antibodies by B cells following the stimulation of MTB-specific antigens. However, little is known about the functional characteristics of these MTB-specific IL-21-producing CD4+ T (TFH) cells. Further investigation is needed with regard to the interaction between TFH and B cells and the molecular mechanisms involved. The present study would focus on the phenotype, key transcription factors and chemokine receptors expression, functional characteristics and regulatory factors. We would further investigate the interaction between TFH and B cells in pleural fluid from tuberculous pleurisy and draining lympho nodes. According to the clinical data of the patients, we could analyze the correlation between TFH cells and the severity and progress of the disease, aiming to clarify the role of TFH in anti-MTB infection and provide new insight into the immune intervention therapy of Tuberculosis.

滤泡辅助T细胞（TFH）是一群以分泌IL-21为特征的独立的辅助性T细胞亚群，对B细胞产生高亲和力抗体和生发中心形成具有关键性调节作用。我们前期研究表明，结核特异性抗原可诱导结核性胸膜炎病人胸水中CD4+T细胞分泌IL-21，在结核特异性抗原刺激下，IL-21可促进B细胞免疫球蛋白的产生。但是，有关这群结核特异性可分泌IL-21的CD4+T细胞（TFH）的功能特征仍知之甚少，其与结核特异性B细胞之间相互作用及分子机制仍待进一步研究证实。本项目拟在前期研究基础上，重点研究人结核特异性抗原诱导的TFH细胞的表型、关键性转录因子和趋化因子受体的表达、功能特征和调控因素；利用结核性胸液及结核病人引流淋巴结样本，研究结核特异性TFH与B细胞的相互作用及其机制。结合病人临床资料，分析TFH亚群的变化与病程、病情及预后的相关性，为阐明结核特异性TFH在结核免疫中的作用及免疫干预治疗开拓新的思路和途径。

我们多年来一直在进行结核杆菌特异性T细胞和B细胞的研究。近期发现，结核杆菌特异性抗原，早期分泌性抗原靶-6（ESAT-6）和培养滤液蛋白-10（CFP-10）主要诱导CD4+T细胞分泌IL-21。一部分分泌IL-21的CD4+T细胞同时可表达Th1细胞因子，但这些细胞不分泌Th2和Th17细胞因子，提示结核杆菌特异性性分泌IL-21的CD4+T细胞与Th1,Th2和Th17亚群不同。同时，结核杆菌特异性分泌IL-21的CD4+T细胞表型为CD45RO+CD62LlowCCR7lowCD40LhighICOShigh。有趣的是，表达Bcl-6的细胞主要集中于CD45RO+ICOS+CD4+T 细胞。分泌IL-21的CD4+T细胞表达Bcl-6水平显著高于不分泌IL-21的CD4+T细胞。而且，IL-12可上调结核杆菌特异性IL-21的产生，尤其是可促进IL-21+IFN-γ+CD4+ T细胞的频率。而且，IL-21可促进结核特异性抗原诱导的免疫球蛋白的分泌。综上，我们的研究表明结核感染局部中结核杆菌特异性产生IL-21的CD4+T细胞在表型及功能上与滤泡辅助性T（Tfh）类似，因此我们称其为“Tfh样”CD4+T细胞，其可能在结核特异性CD4+T细胞应答及体液免疫应答中发挥重要协调作用。