Flow cytometry analysis of endothelial cell surface markers. The anti-GPIbα MoAb Ib-23 binding to nonstimulated cells (A) was compared with its binding to TNFα-stimulated cells (B). Cells were incubated with 10 μg/mL of the primary antibody followed by a 100-fold dilution of FITC-conjugated secondary antibody and examined by flow cytometry. Ib-23 does not recognize endothelial cells, whereas the AP3 anti-β3 subunit MoAb was used as a positive control of both cell populations and the anti–ICAM-1 MoAb was used as a positive control for cell stimulation. The negative controls are represented by the nonshaded peaks. Shaded areas are representative of fluorescence depicted (from left to right) in the presence of Ib-23, AP-3, and anti–ICAM-1 antibody.