EZH2 coordinates memory B-cell programming and recall responses

Antigen-experienced memory B-cells (MBC) are endowed with enhanced functional properties compared to naïve B cells and play an important role in the humoral response. However, the epigenetic enzymes and programs that govern their rapid differentiation are incompletely understood. Here, the role of the histone H3 lysine 27 methyltransferase EZH2 in the formation of MBC in response to an influenza infection was determined in Mus musculus. EZH2 was expressed in all postactivated B-cell subsets, including MBC and antibody-secreting cells (ASC), with maximal expression in germinal center (GC) B cells. Deletion of EZH2 resulted in a skewing of the MBC pool towards a non-GC, IgM+ MBC subset that failed to fully express CCR6 and CD73 at both early and late infection time points. Intriguingly, although EZH2 protein levels were reduced in knockout MBC, deletion was not fully efficient, indicating a strong selective pressure to maintain EZH2 methyltransferase activity. Single-cell RNA-seq of antigen-specific MBC identified a core set of upregulated genes that are likely EZH2 targets across MBC subsets. Finally, defects in the ability to form secondary ASC and GC cells in response to a lethal challenge were observed in EZH2-deficient mice, indicating significant functional impairment in the absence of EZH2. These data show that EZH2 is a critical epigenetic modulator of MBC differentiation and functional potential during reactivation.