Both TNF-α receptors are critical for TNF-α–induced leukocyte rolling. (A) Representative leukocyte rolling profile following mouse TNF-α treatment of WT (○), p75^−/− (▪), p55^−/− (▴), and D^−/− (□) mice. One hour after surgery, TNF-α (2 ng/mL in 25 μL) was applied directly to a 25-mm² area of the cremaster muscle flap. Number of rolling leukocytes in a 100-μm viewing segment was counted in a time window of 2 minutes. Control counts were obtained prior to TNF-α application. (B) Average fold change in early-phase and late-phase rolling leukocytes upon TNF-α treatment of WT (▪), p75^−/− (⊡), p55^−/− (▧), and D^−/− (⊡) mice. Group size equals 4, error bars represent standard deviations (SD), the asterisk indicates statistical significance (P < .05). Leukocyte flux was calculated as described in “Materials and methods” and as follows: (i) Early peak: WT = 6.1 min⁻¹ ± 1.9 min⁻¹, p55^−/−= 3.3 min⁻¹ ± 0.6 min⁻¹, p75^−/−= 3.9 min⁻¹ ± 1.5 min⁻¹; (ii) Late peak: WT = 5.3 min⁻¹ ± 0.8 min⁻¹, p55^−/−= 2.2 min⁻¹ ± 0.4 min⁻¹, p75^−/−= 3.1 min⁻¹ ± 1.1 min⁻¹. Error bars indicate SD.