The cell surface expression of the PAF receptor was examined by flow cytometry as previously described [26] . The cells were harvested from culture flasks using a cell scraper and then incubated with 2.5 μg/mL of mouse anti-PAF receptor monoclonal antibody (11A4 (clone 21); Cayman Chemical, Ann Arbor, MI) or mouse IgG2a, κ isotype control antibody (eBioscience, San Diego, CA). After incubation at 4 • C for 30 min, cells were collected by centrifugation and washed once with Dulbecco's phosphate-buffered saline (PBS (−)). Cell suspensions were incubated with a phycoerythrin-conjugated goat anti-mouse IgG F(ab) 2 fragment antibody (1 : 100 dilution) (Abcam, Cambridge, UK) at 4 • C for 30 min, and the stained cells were assessed with FACSCalibur (BD Bioscience, San Jose, CA).