Induction of stromal networks supports Eμ-Myc lymphoma growth. (A) Congenic recipient mice were transplanted with Wt and CCR7^−/− Eμ-Myc lymphoma cells, as described in Figure 2. Localization of malignant B cells in diseased spleens was visualized by immunofluorescence staining of frozen tissue sections. Wt and CCR7^−/− Eμ-Myc lymphoma cells (blue, CD45.2⁺), gp38⁺ FRC network (red), B-cell zones (green, IgD⁺). Wt Eμ-Myc tumor cell (blue) expansion within and adjacent to the T-cell zone (middle panel: red represents CD3⁺ T cells; and green, dendritic cells, CD11c⁺). Colocalization (in yellow) of gp38⁺ FRC network (red) with the chemokine CCL21 (green) (lower panel). Scale bars represent 100 μm. At higher resolution obtained by confocal microscopy imaging, CCL21 staining largely overlaps with gp38 fluorescence (merged images, yellow; bottom panel, right, representative z-stack). Scale bar represents 25 μm. Data are representative of at least 3 independent experiments, with n = 4 or 5 mice per group. (B-C) Spleen from naive (n = 5) and Wt Eμ-Myc transplanted mice (days 10-13; n = 6) were collagenase-treated, followed by antibody staining and flow cytometric analysis. Percentages of gated gp38⁺/CD45⁻ and CD11b⁺/Gr-1⁺ stroma cells are shown in the plots. *P ≤ .05 for gp38⁺/CD45⁻. P = not significant for CD11b⁺/Gr-1⁺.