LAPCs promote both Tfh differentiation and GC B cell responses in IAV infection in vivo. (a) Both WT (n = 9) and Cxcr3^−/− mice (n = 24) were infected with A/PR/8 virus. On 2 dpi, groups of IAV-infected Cxcr3^−/− mice (n = 18) were inoculated i.v. with 8 dpi LAPCs (mPDCA1⁺CD11c⁻B220⁻TcRβ⁻), DCs (CD11c⁺TcRβ⁻), or B cells (B220⁺CD19⁺CD11c⁻; 5 × 10⁵ cells/mouse), isolated from the dLNs of different A/PR/8 virus–infected B6 mice. 8 dpi, both Tfh (PD-1⁺CXCR5⁺CD4⁺Thy1.2⁺; b) and GC B cells (B220⁺Fas⁺GL-7⁺; c) responses were examined in the dLNs by FACS analysis and were compared between each group of mice. Representative images and data of three independent experiments are shown. The absolute cell numbers of Tfh and GC B cells in the dLN are also shown as mean ± SEM. Considered a significant difference at * (compared with WT) and ** (compared with Cxcr3^−/−, KO), P < 0.05.