Diverging regulation of Bach2 protein and RNA expression determine cell fate in early B cell response.

During the early phase of primary humoral responses, activated B cells can differentiate into different types of effector cells, dependent on B cell receptor affinity for antigen. However, the pivotal transcription factors governing these processes remain to be elucidated. Here, we show that transcription factor Bach2 protein in activated B cells is transiently induced by affinity-related signals and mechanistic target of rapamycin complex 1 (mTORC1)-dependent translation to restrain their expansion and differentiation into plasma cells while promoting memory and germinal center (GC) B cell fates. Affinity-related signals also downregulate Bach2 mRNA expression in activated B cells and their descendant memory B cells. Sustained and higher concentrations of Bach2 antagonize the GC fate. Repression of Bach2 in memory B cells predisposes their cell-fate choices upon memory recall. Our study reveals that differential dynamics of Bach2 protein and transcripts in activated B cells control their cell-fate outcomes and imprint the fates of their descendant effector cells.