The kinetics of Tfh and GC B cell responses correlate with LAPC migration into the dLNs in IAV infection. (a) BALB/c mice (n = 42) were infected intranasally (i.n.) with a sublethal dose (0.05 LD₅₀) of A/PR/8 virus, as described in Materials and methods. At the indicated days after infection, the extent of Tfh (Thy1.2⁺CD4⁺PD-1⁺CXCR5⁺), GC B cell (B220⁺Fas⁺GL-7⁺) and LAPC (mPDCA1⁺CD11c⁻B220⁻TcRβ⁻) responses were determined in the dLNs by FACS analysis. The data are presented as both percent population and absolute numbers (mean ± SEM). Representative stainings from at least three independent experiments are shown. (b) Naive TS-1 cells (Thy1.1⁺CD4⁺) were adoptively transferred into Thy1.2⁺ BALB/c mice (n = 30) by i.v. injection. 24 h after transfer, mice were infected (i.n.) with a sublethal dose (0.05 LD50) of A/PR/8 virus. At the indicated dpi, dLNs were harvested and the extent of the Tfh response of transferred TS-1 cells (Thy1.1⁺CD4⁺PD-1⁺CXCR5⁺) was determined by FACS analysis. The data are presented as absolute numbers (mean ± SEM) in the dLNs. Representative data from two independent experiments are shown. (c) On 5 dpi, both the extent of activation (CD62L and CD44) and Tfh differentiation status (PD-1 and CXCR5) of TS-1 cells were evaluated by comparison with naive TS-1 cells, using FACS analysis. Representative images from two independent experiments are shown.