Proportion of neutrophils trapped between venular endothelial cells and the perivascular basement membrane in IL-1β–treated cremasteric venules from PECAM-1–deficient and wild-type animals as determined by electron microscopy.

Following in vivo quantification of leukocyte responses 4 hours after intrascrotal administration of IL-1β, cremaster muscles of both wild-type and PECAM-1–deficient mice were removed and prepared for electron microscopy. The graph shows the number of neutrophils observed between the venular endothelium and the perivascular basement membrane, expressed as a percentage of the total number of neutrophils that had passed the endothelial cell junctions. The data represent mean ± SEM (14 randomly selected vessel segments from 4 mice per group; *P < .05).