Antibodies against CD99 and CD99L2 inhibit IL-1β–elicited neutrophil extravasation into the peritoneal cavity of PECAM-1–deficient mice. Comparison of the function of (A) CD99 and PECAM-1 and (B) of CD99L2 and PECAM-1. Mice were intravenously injected with 50 μg of the following antibodies in PBS: preimmune co-IgG for negative controls, mAbs against P-selectin and L-selectin (anti–P-/L-selectin) for positive controls, or affinity-purified anti-CD99 IgG (anti-CD99, panel A), or affinity-purified anti-CD99L2 IgG (anti-CD99L2, panel B), immediately followed by intraperitoneal administration of IL-1β. Peritoneal leukocytes were removed 4 hours after stimulation, and neutrophil counts were determined. Results represent 3 independent experiments; for each determination of each experiment, 5 mice were analyzed. ***P < .001. Statistical analysis was done by ANOVA evaluating all available data.