Induction of regulatory functions in BATF3+ B cells through ligand-receptor interactions [ATAC-Seq 2]

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. B cells from Batf3 wildtype and knockout mice were stimulated with either LPS or LPS plus anti-CD40 and IL-21 (LA21). Regions of open chromatin was accessed and compared between conditions using ATAC-seq.作为"效应细胞"，B淋巴细胞可合成抗体。同时，它们还可通过配体-受体相互作用（ligand-receptor interaction）调控免疫功能。鉴于目前对B细胞调控功能的认知较为有限，我们开发了一套研究工作流程，可对B细胞的配体与受体表达进行谱分析，对带有高"特异性评分"的配体所参与的相互作用开展计算机模拟作图，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。借助这一无偏倚研究策略，我们在此报道了一类以转录因子BATF3为标志性特征的新型小鼠B细胞亚群的调控功能。在先天免疫Toll样受体（TLR）、适应性免疫CD40与IL-21受体信号激活B细胞后，可诱导产生BATF3阳性（BATF3+）B细胞，这类细胞会丧失效应细胞功能（即不再产生类别转换抗体），同时表达新型配体，其中最为突出的是细胞因子IL-27与趋化因子CXCL10。经病毒感染与免疫接种诱导产生的IL-27阳性CXCL10阳性（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（IFNγ）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，并通过自分泌的CXCL10-CXCR3相互作用驻留于肿瘤微环境，可上调B细胞的免疫检查点（immune checkpoint）PD-L1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，并为研究免疫细胞间的通信网络提供了范式化研究框架。我们对Batf3野生型与敲除型小鼠的B细胞分别采用脂多糖（LPS），或脂多糖联合抗CD40与IL-21（LA21）进行刺激。通过ATAC测序（ATAC-seq）检测并比较不同处理条件下的开放染色质区域。