Leukocytes were isolated from samples of canine brain tissue and peripheral blood using a previously established and published protocol20 –22 (link) and single cell suspension was created. Cells were stained with anti-canine CD3 (Serotec, NC0522562) conjugated with anti-mouse IgG DyLight 549 (BioRad, STAR117D549GA), anti-canine CD4 PE/Cy7 (eBioscience, 25-5040-42), anti-canine CD8a eFluor 450 (eBioscience, 48-5080-42), anti-mouse/rat FoxP3 APC (eBioscience, 17-5773-82), anti-human CD152-FITC (MyBioSource.com, MBS666569), antihuman PD-1 biotinylated antibody (R&D Systems, BAF1086) conjugated with streptavidin FITC (eBioscience, 11-4317-87), anti-canine CD45 eFluor 450 (eBioscience, 48-5450-42), anticanine CD11c (BioRad, MCA17785) conjugated with anti-mouse IgG FITC (BioRad, STAR117F), anti-human CD123 PE (eBioscience, 12-1239-41), anti-human CD83 APC (MACS, 130-098-889), and anti-human PD-L1 (CD274) PE/Cy7 (BD Bioscience, BDB558017). Cells were analyzed by Flowcytometry, using a BD LSRFOrtessa X-20 cell analyzer, and data was analyzed with FlowJo V.10.2 software.