TBX21 and infection: Importantly, the reverse is also true, in that T-bet can be coexpressed with Bcl6 in precursor Tfh cells both in culture and during infection.4 Originally, it was suspected that T-bet coexpression was transient during Tfh differentiation; however, we and others have demonstrated high expression of T-bet in Tfh cells following infection.5,46,69 The molecular mechanisms of T-bet-Bcl6 coexpression are yet to be defined within Tfh cells.