Optimal CXCR5 expression during Tfh maturation involves the Bhlhe40-Pou2af1 axis.

The pair of transcription factors Bcl6-Blimp1 is well known for follicular T helper (Tfh) early cell fate determination; however, the mechanism(s) for late regulation of CXCR5 during Tfh migration into germinal centers (GCs) is still unclear. In this study, we uncovered another pair of transcription factors, Bhlhe40-Pou2af1, that regulate CXCR5 expression. Pou2af1 was specifically expressed in Tfh cells, whereas Bhlhe40 expression was found to be high in non-Tfh cells. Pou2af1 promoted Tfh formation and migration into a GC by upregulating CXCR5 but not Bcl6, while Bhlhe40 repressed this process by inhibiting Pou2af1 expression. RNA sequencing analysis of antigen-specific Tfh cells generated in vivo confirmed the role of Bhlhe40-Pou2af1 axis in regulating optimal CXCR5 expression. Thus, the regulation of CXCR5 expression and migration of Tfh cells into a GC involves a transcriptional regulatory circuit consisting of Bhlhe40 and Pou2af1, which does not affect the Bcl6-Blimp1 circuit that determines the Tfh cell fate.