Cytofluorometric detection of human endothelial cells in whole blood using S-Endo 1 monoclonal antibody

It has long been debated whether endothelial cells are present at very low frequency in peripheral blood. Elevated concentrations of such circulating cells may represent a good marker of vascular injury. We have therefore designed an immunocytometric assay for the detection of rare endothelial cells in whole blood. This assay is based on a new monoclonal antibody (MAb) S-Endo 1, made against human umbilical vein endothelial cells (HUVEC) and specific for endothelial cells of various origins without detectable reactivity with blood cells. First, the sensitivity of the assay was established by using normal blood samples with admixed HUVEC as an in vitro model. A good correlation was obtained between added and counted endothelial cells; the recovery was greater than 90% and the minimum detectable concentration of HUVEC was about 0.2 cells/microliters whole blood. Using this rapid counting technique, no detectable levels of endothelial cells were found in the blood of normal individuals (CE less than or equal to 0.1 cells/microliters) while elevated concentrations (up to 8 cells/microliters) were detected in a human model of vascular injury corresponding to a traumatic venepuncture. Thus, this new whole blood immunocytometric assay using S-Endo 1 MAb may be useful in determining the levels of circulating endothelial cells in vascular disorders.