IFNG and Zika virus infectious disease: To further demonstrate that Th1-like Tfh cells and Th1-like pre-Tfh cells are the main contributors to IgG2 class switching, we used T-bet-deficient mice in addition to Bcl6f/fCd4-Cre mice, and confirmed that Th1-like Tfh differentiation in ZIKV infection was T-bet dependent, in agreement with a recent study demonstrating that T-bet is important for IFN-γ expression in Tfh cell18.