“…Instead, interstitial fluid drains-in addition to the route of CSF-from the parenchyma into the intramural perivascular spaces between endothelial cells and astrocytic endfeet (Virchow-Robin space) around arterioles and venules of the white matter and basal ganglia toward cervical lymph nodes (Cserr et al, 1981;Lam et al, 2017;Szentistvanyi et al, 1984;Zhang et al, 1990). This ''glymphatic pathway'' is separated from the CSF by the pia mater (Iliff et al, 2012) and is considered a second route of the afferent arm of the immune system, carrying antigens (but not APCs) from the CNS parenchyma to regional lymph nodes (recommended reviews: Engelhardt et al,2016, Ampie andMcGavern, 2022). In the cerebral cortex, the perivascular space is only virtual, in contrast to what was first assumed from erroneous interpretations of sample preparation artefacts (Morris et al, 2016) but instead possess highly permeable fenestrated capillaries that are lined by tanycytes, specialized ependymal and/or glial cells, allowing the passage of peptides and hormones from the CNS to circulating blood (Kaur and Ling, 2017;Wislogki and King, 1936).…”