Mechanism of neutrophil ICAM-1–mediated enhanced effector functions. Whole blood from WT or ICAM-1 KO mice was incubated with LPS (300 ng/mL, 4 hours at 37°C). In some experiments, samples were treated with inhibitors as detailed before addition of ZymTR for a further 15 minutes. Unless indicated, results are presented as percentage inhibition of LPS-stimulated ZymTR phagocytosis. (A) LPS-stimulated samples were treated with blocking antibodies against ICAM-1 (clone YN1/1.7.4) or Mac-1 (clone M1/70) (both at 10 µg/mL for 15 minutes). (B) LPS-stimulated samples were treated with fibrinogen-γ–117-113 peptide to block ICAM-1–fibrinogen interaction (300 µM for 30 minutes). (C) LPS-stimulated samples were incubated with a membrane-penetrating peptide consisting of ¹³C-terminal amino acids of ICAM-1 that inhibits ICAM-1–mediated intracellular signaling (200 µg/mL for 120 minutes at 37°C). (D) LPS-stimulated WT or ICAM-1 KO samples were treated with the Syk inhibitor Piceatannol (30 minutes). (E) Percentage of DHR^pos neutrophils in saline or LPS-stimulated samples following antibody crosslinking of ICAM-1 using rat–anti-ICAM-1 primary antibody (10 µg/mL, 15 minutes) and anti-rat secondary antibody (10 µg/mL, 15 minutes). Data are expressed as mean ± SEM of n = 8 to 15 animals/group. Statistically significant (t test) differences between control and treatment groups: *P < .05, **P < .01, and ***P < .001; differences between WT and ICAM-1 KO treatments: ###P < .001.