Follicle development is associated with conduit remodeling in neonates and allows FDCs to wrap around conduits. (A) WT mice were killed at day 3, 6, or 21 after birth. Axillary and inguinal LNs were harvested, sectioned, and stained for B220 (white), CD3 (blue), collagen IV (green), and FDC-M2 (red) to analyze by confocal microscopy the status of the conduit system in the developing follicles over time. Insets show enlargements of B- and T-cell areas. (B-C) LNs from adult irradiated ubiquitin-GFP mice reconstituted with WT bone marrow were sectioned and stained for collagen IV (red) and FDC-M2 (blue) expression to distinguish by confocal microscopy the very thin processes of the radioresistant GFP-positive (green)–expressing cells present in the follicles. Insets in panel C show an enlargement of a conduit and its enwrapping FDCs in the follicle. Data were acquired using a Leica Sp5 microscope (×20 and ×63 objectives) and are representative of 3 different experiments. Scale bar: 100 μm.