CD4 and viral infectious disease: During the initial phase of an acute viral infection, activated virus-specific CD4+ T cells differentiate into either TH1 or TFH cells.15,55,56 Bcl-6 is required to specify the TFH fate choice,16–18 and Blimp-1 antagonizes this effect by suppressing Bcl-6 expression and Bcl-6-mediated transcriptional activity.16 Thus, the Bcl-6–Blimp-1 balance coordinates the early TFH commitment.