T follicular helper (T_FH) cells are crucial for B cell-mediated humoral immunity¹. Although transcription factors such as BCL6 drive the differentiation of T_FH cells^2,3, it is unclear whether and how post-transcriptional and metabolic programs enforce T_FH cell programming. Here we show that the cytidine diphosphate (CDP)–ethanolamine pathway co-ordinates the expression and localization of CXCR5 with the responses of T_FH cells and humoral immunity. Using in vivo CRISPR–Cas9 screening and functional validation in mice, we identify ETNK1, PCYT2, and SELENOI—enzymes in the CDP–ethanolamine pathway for de novo synthesis of phosphatidylethanolamine (PE)—as selective post-transcriptional regulators of T_FH cell differentiation that act by promoting the surface expression and functional effects of CXCR5. T_FH cells exhibit unique lipid metabolic programs and PE is distributed to the outer layer of the plasma membrane, where it colocalizes with CXCR5. De novo synthesis of PE through the CDP–ethanolamine pathway co-ordinates these events to prevent the internalization and degradation of CXCR5. Genetic deletion of Pcyt2, but not of Pcyt1a (which mediates the CDP–choline pathway), in activated T cells impairs the differentiation of T_FH cells, and this is associated with reduced humoral immune responses. Surface levels of PE and CXCR5 expression on B cells also depend on Pcyt2. Our results reveal that phospholipid metabolism orchestrates post-transcriptional mechanisms for T_FH cell differentiation and humoral immunity, highlighting the metabolic control of context-dependent immune signalling and effector programs.

T 滤泡辅助 (T _FH ) 细胞对于 B 细胞介导的体液免疫至关重要¹。尽管 BCL6 等转录因子驱动 T _FH细胞的分化^2,3，但转录后和代谢程序是否以及如何强制执行 T _FH细胞编程尚不清楚。在这里，我们表明胞苷二磷酸 (CDP)-乙醇胺途径协调 CXCR5 的表达和定位与 T _FH的反应细胞和体液免疫。在小鼠中使用体内 CRISPR-Cas9 筛选和功能验证，我们鉴定了 ETNK1、PCYT2 和 SELENOI——CDP-乙醇胺途径中用于从头合成磷脂酰乙醇胺 (PE) 的酶——作为 T _FH细胞分化的选择性转录后调节因子通过促进 CXCR5 的表面表达和功能效应发挥作用。T _FH细胞表现出独特的脂质代谢程序，PE 分布到质膜的外层，在那里它与 CXCR5 共定位。通过 CDP-乙醇胺途径从头合成 PE 可协调这些事件以防止 CXCR5 的内化和降解。Pcyt2基因缺失，但Pcyt1a不缺失 （介导 CDP-胆碱途径），在活化的 T 细胞中会损害 T _FH细胞的分化，这与体液免疫反应降低有关。B 细胞上 PE 和 CXCR5 表达的表面水平也取决于Pcyt2。我们的结果表明，磷脂代谢协调了 T _FH细胞分化和体液免疫的转录后机制，突出了环境依赖性免疫信号和效应程序的代谢控制。