Platelet adhesion to VWF is inhibited by β₂ GPI. Glass coverslips were coated with VWF (10 μg/mL) and subsequently incubated with PBS (A), β₂ GPI (2.2 μM; B), or β₂ GPI and a monoclonal anti–β₂ GPI antibody with LA activity (both 2.2 μM; C). Reconstituted blood supplemented with PBS, β₂ GPI, or β₂ GPI/anti–β₂ GPI antibody was then perfused over these coverslips at a shear rate of 300 s⁻¹. After perfusion, adhered platelets were fixed in PBS/0.5% glutaraldehyde, dehydrated in methanol, and stained with May-Grünwald and Giemsa. Adhered platelets were visualized using light microscopy (Leitz Diaplan; Leica, Rijswijk, the Netherlands) equipped with a CCD camera (JAI-CV-235C, Copenhagen, Denmark) and computer-assisted analysis (AMS 40-10 Saffron, Walden, United Kingdom). Original magnification was 400 × (40×/1.00 NA objective lens). Dark regions represent platelet aggregates. (D) Platelet adhesion was evaluated using computer-assisted analysis and expressed as the percentage of surface covered with platelets. To compare experiments, platelet coverage on VWF in the presence of PBS was set to be 100% and relative coverage was calculated for the other conditions. Data represent the mean (± SD) of 3 experiments. *P < .03, **P < .003.