Heterogeneity of rabbit aortic endothelial cells in primary culture.

Factor VIII-related antigen (F8-RAg) and angiotensin-converting enzyme (ACE) are accepted diagnostic markers of endothelial cells in culture. However, when we isolated cells from rabbit thoracic aorta (after collagenase treatment and gentle scraping of the intima) and examined them with immunoperoxidase techniques, we observed two cell types which stained specifically for either F8-RAg or ACE, but not both. Each cell type was morphologically distinguishable in primary culture. F8-RAg-positive cells were recognizable in distinct patches as more elongated, tightly apposed, and firmly adherent cells; they exhibited only faint or no staining for ACE and no accumulation of a fluorescent, acetylated low-density lipoprotein probe (DiI-Ac-LDL), another endothelial cell marker. In contrast, ACE-positive cells were more rounded, less closely apposed, and grew as strict monolayers that exhibited a characteristic cobblestone appearance at confluence; ACE-positive cells were F8-RAg negative, but demonstrated intense labeling with DiI-Ac-LDL. Subcultures of ACE-positive cells were also stained by anti-rabbit thrombomodulin.