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Summary. In pathological conditions such as sickle cell disease, falciparum malaria and diabetes, an abnormal adherence of erythrocytes to endothelium is concomitant with loss of phospholipid asymmetry resulting in phosphatidylserine (PS) exposure. We have investigated the involvement of PS in this interaction by studying adhesion of human erythrocytes, treated with Ca 2 -ionophore A23187 in combination with N-ethylmaleimide, to human umbilical vein endothelial cells in a¯ow-based assay. Results showed that erythrocytes which exposed PS, massively adhered to HUVEC in a Ca 2 -dependent manner. This adhesion was inhibited by PS liposomes and by annexin V, giving clear evidence of the PS dependence of these interactions.

A flow cytometric method to detect apoptotic cells is described. This method is based on the detection of differences in chromatin condensation with Hoechst 33342 as a probe and the detection of dead cells with propidium iodide as a probe for membrane damage. By this method it was possible to detect, in the same sample and at the same time, intact cells, cells undergoing apoptosis, and dead cells resulting from apoptotic and/or necrotic processes. The method was successfully applied to the detection of apoptotic cells in two human cell models: cultured polymorphonuclear cells and the U937 cell line treated with antitumoral drugs. Staining specificity for apoptotic cells was controlled by cell sorting of the presumed apoptotic population, followed by morphologic examination or DNA analysis of the sorted populations. The usefulness of such a method is discussed in terms of applications in the analysis of heterogeneous clinical samples, populations with low DNA degradation during apoptosis, and cell cycle position of the apoptotic cells.