Mice were perfused with 0.1M PBS for 5min. Heads were removed and skulls were quickly stripped. Mandibles were removed, as well as all skull material rostral to maxillae. Surgical scissors were used to remove the top of the skull, cutting clockwise, beginning and ending inferior to the right post-tympanic hook. Meninges (dura mater, arachnoid and pia mater) were carefully removed from the interior aspect of the skulls and surfaces of the brain with Dumont #5 forceps (Fine Science Tools). Meninges were gently pressed through 70μm nylon mesh cell strainers with sterile plastic plunger (BD Biosciences) to yield a single cell suspension. For lymphatic endothelial cells isolation, meninges (along with diaphragm and ear skin) were digested for 1h in 0.41U/ml of Liberase TM (Roche) and 60U/ml of DNAse1. Cells were then centrifuged at 280g at 4°C for 10 min, the supernatant was removed and cells were resuspended in ice-cold FACS buffer (pH 7,4; 0.1M PBS; 1mM EDTA: 1% BSA). Cells were stained for extracellular marker with antibodies to CD45-PacificBlue (BD Bioscience), CD45-PE-Cy7 or eFluor 450 (eBioscience), TCRβ-Alexa780 (eBioscience), CD4-Alexa488 (eBioscience), CD8-PerCPCy5.5 (eBioscience), CD44-APC (eBioscience), CD62L-PE (eBioscience), CD71-APC (eBioscience), podoplanin-PE (eBioscience), CD31-Alexa647 (eBioscience), B220-PE (eBioscience), CD19-BB515 (BD Bioscience). Except for the lymphatic endothelial cells identification experiment, all cells were fixed in 1% PFA in 0.1M pH 7.4 PBS. Fluorescence data were collected with a CyAn ADP High-Performance Flow Cytometer (Dako) or a Gallios (Beckman Coulter) then analyzed using Flowjo software (Treestar). To obtain accurate cells counts, single cells were gated using the height, area and the pulse width of the forward and side scatter, then cells were selected for being live cells using the LIVE/DEAD Fixable Dead Cell Stain Kit per the manufacturer’s instructions (Invitrogen). The cells were then gated for the appropriate markers for cell type (Extended Data Fig. 3,9). Experiments were performed on meninges from n = 3 mice per group. Data processing was done with Excel and statistical analysis was performed using GraphPad Prism.