ACLY integrates metabolism and chromatin accessibility to enable B Cell activation and humoral immunity

B cell activation and differentiation into antibody-secreting cells require extensive metabolic and epigenetic remodeling, yet the molecular mechanisms that integrate these programs remain incompletely understood. ATP-citrate lyase (ACLY) links glucose metabolism to acetyl-CoA production, supporting lipid biosynthesis and protein acetylation. However, its role in humoral immunity has not been fully defined. Here, using genetic and integrated multi-omics approaches, we show that B cell activation is accompanied by coordinated metabolic, transcriptional, and epigenetic reprograming. Although ACLY is dispensable for B cell development and homeostasis, it is required to establish chromatin accessibility programs in activated B cells, with a more pronounced impact on the epigenetic landscape than on transcriptional output. ACLY-deficient B cells exhibit profound defects in TLR and BCR elicited activation, survival and metabolic fitness ex vivo. In vivo, B cell-intrinsic loss of ACLY results in impaired antigen-specific antibody production, associated with reduced germinal center and plasmablast formation, but normal homeostatic proliferation. Deletion of ACLY after B cell activation reduces plasmablast generation in vivo, indicating a continued requirement for ACLY beyond the initial activation phase. Together, these findings identify ACLY as a central regulator that links metabolism to epigenetic programing that supports B cell activation and humoral immunity.