P-selectin triggers αMβ2 clustering. (A) Neutrophils were treated without (control) or with human IgG (hIgG), P-selectin Ig chimera (P-sel Ig), and PMA. After fixation, samples were stained by mAb IB4 to β2 subunit or mAb OKM1 to αM subunit followed by Alexa Fluor 488–conjugated goat antibody to mouse IgG and confocal laser scanning microscopy. The data presented here are representative images from 3 independent experiments. (B) The mean ± SD values of fluorescence intensities of the particles are presented for mAb IB4-stained (i) and mAb OKM1-stained (ii) neutrophils. These were quantified by image analyses using the ImagePro Plus program. The differences between hIgG and control were statistically insignificant (P > .05), whereas the differences between P-sel Ig or PMA and control were statistically significant (P < .01).