PRDM1 and viral infectious disease: Transcription factor-1 (TCF-1) initiates the TFH fate commitment by directly inducing Bcl-6 expression and suppressing Blimp-1 expression during an acute viral infection.15,26,27 Although TCF-1 is expressed at high levels in naïve CD4+ T cells,28 activated virus-specific CD4+ T cells must further increase TCF-1 expression levels for subsequent TFH conversion following an acute viral infection.15 Currently, additional factors that are responsible for the early induction of the fate commitment of TFH cells remain to be determined.