IL-7–Cre transgene expression in adult murine LNs. (A) Inguinal LN cell suspensions were depleted of CD45⁺ cells, and CD45⁻ stromal cells were analyzed by flow cytometry for CD31 and Pdpn expression. Stromal cell subpopulations are designated in the respective quadrant. DN indicates double-negative cells. (B) FACS-sorted LN stromal cells were analyzed for IL-7 expression by quantitative RT-PCR (n = 4 from 2 independent sorts). (C) Histograms displaying EYFP expression within LEC and FRC subpopulations, IL-7–CrexR26-EYFP (solid line), and C57BL/6 (gray shading) LNs. Values indicate mean percentage ± SEM of EYFP⁺ cells (n = 6 in independent preparations). (D) Confocal laser scanning microscopic analysis of inguinal LNs from IL-7–CrexR26-EYFP mice. Scale bar represents 200 μm. (E) High magnification of boxed area in panel D; indicated are transgene-expressing LECs (arrows) and FRCs (asterisks). Scale bar represents 50 μm. (F) Anti-CD169 staining in the subcapsular sinus region of an IL-7–CrexR26-EYFP inguinal LN. Scale bar represents 20 μm. (G) Flow cytometric analysis of human CD25 expression on EYFP⁺ (black line) and EYFP⁻ (gray line) LN stromal cells from triple transgenic IL-7–hCD25xIL-7CrexR26-EYFP mice.