CSF drainage from the cribriform plate into the nasal cavity. (A) Sagittal view of the nasal cavity and forebrain 45 min after Th-Lb injection of OVA-A555 (magenta) and labeled with LYVE1 (green). Tracer deposits were detected in meningeal perivascular spaces, the cribriform plate (CP), and throughout the olfactory epithelium (OE) and the respiratory epithelium (RE) of the nasal cavity. Dotted line, limit between intra and extracranial regions; dashed lines, nasopharynx (NP); blue arrowheads, CAV; OB, olfactory bulb. (B–E) Lymphatics of the cribriform plate. Lymphatic vasculature (LYVE1⁺, green in B and C; PROX1⁺, green in E), meningeal veins (vWF, blue in D), and tracer deposits (magenta) on sagittal (B and E) and coronal (C and D) views of the CP. MLVs were located in the dura of the ethmoid bone (lymphatic bed 7, green arrowheads) and around CP foramina (orange arrowheads in B and C). No LYVE1⁺ vessels were found to cross the CP toward the olfactory epithelia (B and E), while the outflow of tracer filled the OE and RE (A and D). Inset in B: Magnification of dotted frame showing tracer-labeled phagocytic cells (yellow arrowheads) concentrated close to the ethmoid MLVs. Ethmoid MLVs (C) are not associated with vWF⁺ blood vessels (D). (E) The ethmoid MLVs (white arrowheads) converge dorsally with the lymphatic vessels prolonging the SOS and exit the nasal cavity via the posterior ethmoid foramen (pef) and the foramen cecum (fc). SP, septum. (F and G) Lymphatic vessels of the nasal cavity. Sagittal views showing the tracer-labeled LYVE1⁻ vasculature of the OE (F, magenta), the LYVE1⁺ lymphatics of the basal RE and the NP (F, green), and the Vegfr3-expressing vessels of the OE (GFP reporter, green in G). (H) Sagittal schematic of lymphatic circuits of the nasal cavity. Ethmoid MLVs (LYVE1⁺, light green, 7) do not cross the CP along with olfactory nerves but exit rostrally into the nasal cavity via the pef and fc. OE lymphatics (PROX1⁺/VEGFR3⁺/LYVE1⁻, bluish green) transport CSF, likely collected from perineural drainage along olfactory nerves, then drain into LYVE1⁺ vessels (dark green) of the basal RE and NP that collect into cervical LNs. (I–K) Lymphatic drainage from the orbital cavity. Tracer deposits (OVA-A⁵⁵⁵, magenta) and lymphatic vasculature (green in I and J). (I) Ventrolateral view of the nasal lacrimal sac region (NLS, dashed line) shows tracer deposits between the orbital cavity under the eye (E) and the olfactory epithelium (OE). Orbital LYVE1⁺ lymphatics connect with facial lymphatics (white arrowheads). (J) Lymphatic tracer uptake by orbital PROX1⁺ vessels (white arrowhead). (K) Macroscopic imaging of a mouse head 10 min after ICM injection with OVA-A⁵⁵⁵ (magenta) and intra-ocular delivery of OVA-A⁴⁸⁸ (green). Both OVA-A⁴⁸⁸ and OVA-A⁵⁵⁵ collected into the associated mandibular LNs (white); only OVA-A⁵⁵⁵ drained into the mandibular LNs (magenta). (L–N) Lymphatic drainage from the nose. (L) Coronal view of the nose showing two drainage circuits: dorsal (white arrowheads) and ventral (yellow arrowheads). Dashed circles show the distal part of NLD with LYVE1⁺ LVs (green) costained with OVA-A⁵⁵⁵ (magenta). (M) Macroscopic imaging of mandibular LNs (mLN, green arrowhead) labeled with OVA-A⁴⁸⁸ 5 min after nostril OVA⁴⁸⁸ injection. (N) Sagittal schematic of lymphatic drainage circuits from the orbital cavity and the nose toward cervical LNs. A, anterior; D, dorsal; L, lateral; P, posterior; PEF, posterior ethmoid foramen; V, ventral. Scale bar: 180 μm (insert in B); 500 μm (A–C, E–J, and L); 80 μm (D); 2 mm (K and M).