IFNG and influenza: Of note, Tfh cell expression of T-bet is required to regulate the expression of key Th1 factors, IFN-γ, and CXCR3, although a recent fate-mapping study demonstrated that Tfh cells could continue to express IFN-γ even when T-bet expression was transient.46,69,70 T-bet-deficient Tfh cells and their precursors promote B-cell isotype switching toward IgG1 during influenza infection, potentially through the loss of IFN-γ and other alterations of Tfh cytokine production.46