CSF drainage through the cribriform plate and inside the nasal cavity. (A–F) Pattern of tracer 45 min after ICM (A) or Th-Lb (B–F) injections of OVA-A⁵⁵⁵ (magenta) or ink. (A and B) Sagittal (A) and coronal (B) views of the ethmoid MLVs (7). Note tracer deposits at the cribriform plate (CP) border and in LYVE1⁺ (A, green arrowhead) and PROX1⁺ (B, green arrowhead) MLVs around olfactory nerve foramina (orange arrowheads). Dotted line, limit between intra- and extracranial regions; OB, olfactory bulb; OE, olfactory epithelium. (C–F) Sagittal (C–E) and coronal (F) views of nasal cavity lymphatics. Tracer deposits (magenta in C, D, and F; ink in E) are colocalized with lymphatic markers: PROX1 (C, green), VEGFR3-YFP (D, green), and LYVE1 (E and F). (C) PROX1⁺ lymphatics in the turbinate, on the outer aspect of the CP (white arrows in C). (D) VEGFR3⁺ lymphatics transporting OVA-A⁵⁵⁵ tracer in the OE (white arrowheads). (E) Two contiguous paraffin sections of the nasal cavity showing ink tracer (black arrowheads) inside narrow LYVE1⁻ vessels and collecting LYVE1⁺ lymphatics in the respiratory epithelium (RE). (F) LYVE1⁺ lymphatics, including tracer-labeled vessels around the nasopharynx (NP). SP, septum. (G) Lymphatic drainage from the orbital cavity. Coronal view showing tracer deposits (magenta) and pattern of LYVE1⁺ lymphatics (green). Lymphatic-tracer uptake is detected around the nasal lacrimal sac (NLS, white labeling, arrowheads). E, eye. (H and I) Lymphatic drainage from the nose 90 min after intraspinal OVA-A⁵⁵⁵ injection (magenta). Macroscopic (H) or LSFM (I) imaging showing tracer accumulation at the level of the nostril (white arrowheads in H and I) and tracer drainage along dorsal and ventral nasal veins (white arrows in H). Note LYVE1⁺ lymphatics in the nostril (arrowheads in the magnified frame in I) and along nasal veins (arrows in I). Scale bar: 300 μm (A, H, and I, insert in I); 150 μm (B–F).