Histological characterization of the MRR of the LN. (A and B) Frozen LN sections from WT mice given 70-kD tetramethylrhodamine-labeled dextran (red) 30 min before excision. (A) ER-TR7 staining (grey) identifies the following nodal regions: MRR, macrophage-rich region; PIR, peripheral interfollicular region; CA, capsule; SCS, subcapsular sinus; CR, cortical ridge; B, B cell follicle; T, T cell zone. (B) Mosaic-tiled confocal images of whole LNs stained with different Abs (grey, left images), and higher magnification images of staining of the MRR (right images). (C) Number of dextran⁺ cells per node per cell type as determined by node dissociation followed by flow cytometry. Cells were gated on FITC-dextran positivity and divided into CD11b⁺ DCs (CD11c⁺CD11b⁺ cells), CD11b⁻ DCs (CD11c⁺CD11b⁻ cells), and macrophages (CD11c⁻CD11b⁺ cells). Macrophages were further gated on F4/80 to identify medullary macrophages (F4/80⁺). Dextran⁺ cells belonging to each population were quantified using flow cytometric percentages and total node counts. (D) MPM images from CD11c-eYFP mice given dextran. Bottom panels show higher magnification. CD11c⁺ cells (green), collagen (second harmonic generation, blue), dextran⁺ cells (red). (E) High-magnification confocal image of whole-mounted CD11c-eYFP LNs after dextran administration. CD11c⁺ cells (green), dextran⁺ cells (red). Scale bars are shown in micrometers. We made similar observations in at least three additional experiments per image.