To obtain a suspension of meningeal lymphatic endothelial cells (LECs) from the meninges of young-adult (2–3 months) and old (20–24 months) mice by FACS, mice were euthanized by i.p. injection of Euthasol and transcardially perfused with ice cold PBS with heparin. Skullcaps were quickly collected and meninges (dura mater and arachnoid) were dissected using Dumont #5 forceps in complete media composed of DMEM (Gibco) with 2% FBS (Atlas Biologicals), 1% L-glutamine (Gibco), 1% penicillin/streptomycin (Gibco), 1% sodium pyruvate (Gibco), 1% non-essential amino-acids (Gibco) and 1.5% Hepes buffer (Gibco). Individual meninges were then incubated with 1 mL of complete media with 1.4 U/mL of Collagenase VIII (Sigma-Aldrich) and 35 U/mL of DNAse I (Sigma-Aldrich) for 15 min at 37°C. Individual samples consisted of cell suspensions pooled from 10 meninges that were obtained after filtration through a 70 μm nylon mesh cell strainer. Cell suspensions were then pelleted, resuspended in ice-cold FACS buffer containing DAPI (1:1000, Thermo Fisher Scientific), anti-CD45-BB515 (1:200, clone 30-F11, BD Biosciences), anti-CD31-Alexa Fluor® 647 (1:200, clone 390, BD Biosciences) and anti-Podoplanin-PE (1:200, clone 8.1.1, eBioscience) and incubated for 15 min at 4°C. Cells were then washed and resuspended in ice-cold FACS buffer. Briefly, singlets were gated using the pulse width of the side scatter and forward scatter. Cells negative for DAPI were selected for being viable cells. The LECs were then gated as CD45−CD31+Podoplanin+ (see Extended data Fig. 6 for representative dot plots) and sorted into a 96-well plate containing 100 μL of lysis buffer (Arcturus PicoPure RNA Isolation Kit, Thermo Fisher Scientific) using the Influx™ Cell Sorter (BD Biosciences) that is available at the University of Virginia Flow Cytometry Core Facility.