Induction of regulatory functions in BATF3+ B cells through ligand-receptor interactions [RNA-Seq 3]

As “effector” cells, B lymphocytes make antibodies. They also regulate immune functions through ligand-receptor interactions. The limited understanding of regulatory roles of B cells prompted us to develop a workflow that profiles B cell ligand and receptor expression, maps in silico interactions involving ligands with high “specificity scores”, validates the function of top ligand-receptor interactions, and unveils transcription regulation of specific ligands. Using this unbiased approach, here we report the regulatory functions of a new subset of murine B cells that express BATF3 as a hallmark transcription factor. BATF3+ B cells, as generated upon B cell activation by innate TLR and adaptive CD40 and IL-21 receptor signals, lose their effector cell function (making class-switched antibodies) while expressing new ligands, most notably cytokine IL-27 and chemokine CXCL10. As elicited by viral infection and immunization, IL-27+CXCL10+ B cells target effector B cells through the IL-27 receptor and, together with IFNg, optimize the antibody response and anti-viral immunity. Also appearing in tumors and retained there through the autocrine CXCL10-CXCR3 interaction, they enhance B cell expression of immune checkpoint PD-L1 and suppress anti-tumor immunity. Thus, we have identified new regulatory B cells and provided a paradigmatic framework to investigate immune cell communications. RNA-seq samples from 4 different B cell stimulation conditions, namely CD154, CD154 plus IL-27, CD154 plus IFNg, and CD154 plus IL-21 were used in analysis.

作为效应细胞（effector cell），B淋巴细胞（B lymphocytes）可合成抗体，同时还可通过配体-受体相互作用（ligand-receptor interaction）调控免疫功能。鉴于当前学界对B细胞调控功能的认知仍存在局限，我们开发了一套标准化分析流程，可完成B细胞配体与受体的表达谱分析、对携带高“特异性得分（specificity score）”的配体所参与的虚拟（in silico）相互作用进行映射、验证核心配体-受体相互作用的功能，并揭示特定配体的转录调控机制。借助这一无偏分析策略，本研究报道了一类以转录因子BATF3为标志性特征的小鼠B细胞新亚群的调控功能。BATF3阳性（BATF3+）B细胞可在固有免疫Toll样受体（Toll-like receptor, TLR）、适应性免疫相关CD40以及IL-21受体信号介导的B细胞活化过程中产生；这类细胞会丧失效应细胞功能（不再分泌类别转换抗体），同时表达新型配体，其中最具代表性的为细胞因子IL-27与趋化因子CXCL10。在病毒感染与免疫接种过程中诱导产生的IL-27+CXCL10+ B细胞可通过IL-27受体靶向效应B细胞，并与干扰素γ（Interferon-γ, IFNG）协同优化抗体应答与抗病毒免疫。这类细胞同样会出现在肿瘤组织中，并通过自分泌CXCL10-CXCR3相互作用驻留于肿瘤微环境；它们可上调B细胞免疫检查点（immune checkpoint）PD-L1的表达，并抑制抗肿瘤免疫。综上，我们鉴定出了一类新型调控性B细胞，并为免疫细胞通讯的研究提供了范式化研究框架。本分析采用了4种不同B细胞刺激条件下的RNA测序（RNA-seq）样本，具体包括CD154、CD154联合IL-27、CD154联合IFNG以及CD154联合IL-21。