Neutrophils were fixed in 4% paraformaldehyde with 50 mM HEPES buffer for 20 min at room temperature, followed by 15 min of 0.1% triton X-100, and 15 min of 0.2% BSA in PBS. Anti-human CEACAM1 mAb T84.1 was then added to the fixed cells at a final concentration of 1 mg/mL for 1 hour. After 3 washes with PBS, goat anti-mouse Alexa 555-conjugated antibody (Invitrogen, Eugene, OR) was added at the concentration of 2 mg/ mL for another 30 min followed by 3 washes with PBS. Stained cells were plated on glass slides with Hard Set mounting medium and counterstained with DAPI from Vector Laboratories Inc (Burlingame, CA 94010, USA). Confocal microscopy was performed on a Zeiss Model 310 (Oberkochen, Germany) confocal microscope.