Blocking CD99 inhibits ear swelling. Mice were either not sensitized (first bar, not sens.) or sensitized with DNFB (all other bars) 5 days prior to challenging one of the ears with DNFB. Immediately prior to challenging, mice were intravenously injected with 100 μg anti-CD99 or 150 μg anti–E- and anti–P-selectin antibodies in PBS or with PBS alone (as indicated). Rabbit preimmune IgG was used as negative control IgG (co-IgG). The ear swelling response 10 hours after challenge is expressed as the difference (μm) between the thickness of the challenged ear and the thickness of the vehicle-treated ear. Results are representative for 3 similar experiments; for each determination 5 mice were analyzed. P < .000 05, co-IgG versus anti-CD99 or anti–E-/P-selectin. Results are presented as mean ± SEM and are representative of at least 3 separate experiments.