C57BL/6 Mouse Primary Pulmonary Vein Microvascular Endothelial Cells from Cell Biologics are isolated from pulmonary vein of pathogen-free laboratory mice and grown in gelatin pre-coated tissue culture flask with Cell Biologics’ Complete Growth Medium. Cells at passage 3 are harvested from flasks and cryo-preserved in vials. Each vial contains 0.5x106 cells per ml and is delivered frozen. C57BL/6 Mouse Primary Pulmonary Vein Microvascular Endothelial Cells are characterized by immunofluorescence staining with antibodies of VE-cadherin (CD144, VE-cadherin Antibody, C-19, sc6458, Santa Cruz), AF1002 (R&D System) or CD31/PECAM-1 (Catalog No. 553370, BD). These cells are negative for bacteria, yeast, fungi, and mycoplasma and can be expanded for 3-5 passages at a split ratio of 1:2 under the cell culture conditions specified by Cell Biologics. Repeated freezing and thawing of cells is not recommended.