Metabolic Reprogramming Induces Germinal Center B Cell Differentiation through Bcl6 Locus Remodeling

The germinal center (GC) reaction is essential for long-lived humoral immunity. However, molecular requirements for the induction of Bcl6, the master regulator for GC B cell differentiation, remain unclear. Through screeningfor cytokines and other stimuli that regulateBcl6 expression, we identify IL-4 as the strongest inducer. IL-4 signaling alters the metabolomic profile in activated B cells and induces accumulation of the TCA cycle intermediate a-ketoglutarate (aKG), which is required for activation of the Bcl6 gene locus. Mechanistically, after IL-4 treatment, STAT6 bound to the known enhancers in the Bcl6 locus recruits UTX, a demethylase for the repressive histone mark H3K27me3 that requires aKG as a cofactor. In turn, the H3K27me3 demethylation activates the enhancers and transcription of the Bcl6 gene. We propose that IL-4-mediatedmetabolic reprogramming in B cells is pivotal for epigenomic activation of Bcl6 expression to promote GC B cell differentiation.