STAT4 and T-bet control follicular helper T cells development in viral infections [ATAC-seq]. STAT4 and T-bet control follicular helper T cells development in viral infections [ATAC-seq]

Follicular helper T (Tfh) cells promote germinal center (GC) B cell survival and proliferation, and guide their differentiation and Ig isotype switching by delivering contact-dependent and soluble factors, including IL-21, IL-4, IL-9, and IFN-g. IL-21 and IFN-g are co-expressed by Tfh cells during acute and chronic infections, but transcriptional regulation of these cytokines in the GC is incompletely understood. We show that the Th1 transcriptional regulators T-bet and STAT4 are co-expressed with Bcl6 in Tfh cells following acute murine lymphocytic choriomeningitis virus infection, albeit with temporal decline in T-bet expression as the GC response evolved. T-bet was important for Tfh cell production of IFN-g, but not IL-21, and for the generation of a robust germinal center reaction. STAT4, phosphorylated in Tfh cells upon infection, was required for their expression of T-bet and Bcl6, and that of IFN-g and IL-21. These data indicate that T-bet is concomitantly expressed with Bcl6 in Tfh cells and is required alongside STAT4 phosphorylation to coordinate Tfh cell IL-21 and IFN-g production, and for promotion of the GC response following acute viral challenge. Overall design: Each group consisted of 5 mice pooled together. Two replicates of each group were used for ATAC-seq. Two groups were studied: Wild-type and homozygous STAT4 knockout mice.

滤泡辅助性T细胞（Follicular helper T cells，Tfh）可通过接触依赖途径及分泌包含白细胞介素21（IL-21）、白细胞介素4（IL-4）、白细胞介素9（IL-9）与干扰素γ（IFN-γ）在内的可溶性因子，促进生发中心（germinal center，GC）B细胞的存活与增殖，并调控其分化与免疫球蛋白类别转换。在急性与慢性感染过程中，Tfh细胞会共表达IL-21与IFN-γ，但目前对于生发中心内这些细胞因子的转录调控机制仍不完全明晰。本研究显示，在小鼠急性淋巴细胞性脉络丛脑膜炎病毒感染后，Th1转录调节因子T-bet与STAT4可与Bcl6在Tfh细胞中共表达，尽管随着生发中心应答的进展，T-bet的表达会随时间出现下降。T-bet对Tfh细胞产生IFN-γ而非IL-21具有重要作用，同时对于形成稳健的生发中心反应也是必需的。感染后在Tfh细胞中发生磷酸化的STAT4，是Tfh细胞表达T-bet、Bcl6以及IFN-γ和IL-21的必要条件。上述数据表明，T-bet可与Bcl6在Tfh细胞中协同表达，且需与STAT4磷酸化共同发挥作用，以协调Tfh细胞分泌IL-21与IFN-γ，并促进急性病毒攻击后的生发中心应答。总体实验设计：每组包含5只合并的小鼠，每个组设置2次生物学重复用于转座酶可及性测序（ATAC-seq）。本研究设置两组小鼠：野生型小鼠与纯合STAT4敲除小鼠。