LAPC migration into the dLNs is CXCR3 dependent. (a) LAPCs (mPDCA1⁺CD11c⁻B220⁻TcRβ⁻) cell surface CXCR3 expression was examined by FACS analysis, using cells isolated from IAV-infected lungs (n = 12) on 3 and 6 dpi. Representative images of three independent experiments are shown. (b) At the indicated dpi, Cxcl9 gene expression was determined by qPCR, either in total dLN cells (n = 24) or in each of the indicated cell populations isolated from the dLN of IAV-infected mice (n = 6). Representative data of two independent experiments are shown. To determine whether CXCR3–CXCL9 interactions are involved in LAPC migration into the dLN, an in vivo migration assay was performed using Cxcr3^−/− mice. (c) Both WT (n = 9) and Cxcr3^−/− mice (n = 9) were infected with IAV, and then FITC-dextran was administered i.n. on 5 dpi. 24 h later, cells were isolated from the dLNs and the extent of migratory LAPCs was determined by FACS analysis. Numbers indicate the percentage of FITC⁺ cells within the LAPC population. The absolute cell number of FITC⁺ LAPCs in the dLN was also determined and is shown as mean ± SEM. Representative data of two independent experiments are shown. (d) Both WT (n = 12) and Cxcr3^−/− (n = 12) mice were infected with IAV. At 8 dpi the accumulation of LAPCs (mPDCA1⁺CD11c⁻B220⁻TcRβ⁻) in the dLN was examined by FACS analysis. Representative data of at least three independent experiments are shown. (e) Mixed BM chimera containing WT and Cxcr3^−/− BM at a 1:1 ratio were generated as described in Materials and methods. At 8 wk after reconstitution, mice (n = 6) were infected with A/PR/8 virus. At 8 dpi, the ratio between WT and Cxcr3^−/− LAPCs (mPDCA1⁺CD11c⁻B220⁻TcRβ⁻) was determined in the dLNs by FACS analysis. Representative images and data of at least two independent experiments are shown. *, P < 0.05.