Expansion of IL-7–expressing stromal cells during virus-induced LN remodeling. IL-7–CrexR26-EYFP mice were infected with 200 pfu LCMV-WE, and transgene activity was determined on day 20 after infection. (A) In situ analysis of naive (upper panels) and infected (lower panel) IL-7–CrexR26-EYFP inguinal LNs (blue represents B220; red, Pdpn; and green, EYFP). Scale bar represents 200 μm. (B) Higher magnification of day 20 IL-7–CrexR26-EYFP inguinal LNs (red represents LYVEI; blue, Pdpn; and green, EYFP). Scale bar represents 100 μm. (C-D) Enumeration of EYFP⁺ and EYFP⁻ FRCs (C) and LECs (D) in LNs from naive and LCMV-infected mice (mean ± SEM; n = 6 mice). (E) Flow cytometric FACS analysis of EYFP⁺ FRCs (C) and LECs (D) in LNs taken from naive and infected IL-7–CrexR26-EYFP mice. (E) Evaluation of transgene activity in LECs in LNs of naive (left column) and LCMV-infected mice (right column). Cortical, paracortical, and medullary sections were stained for lymphatic endothelium (LyveI, red) and transgene activity (EYFP, green). (F) Quantification of EYFP and LyveI mean fluorescence intensity (MFI) in the different LN regions (mean ± SEM; n = 6 mice). (G) Proportion of EYFP⁺ areas in cortical LN sections from naive and infected mice. *P < .05; **P < .01; and n.s. indicates not significant.