Enhancement of LPS-induced respiratory burst and IL-8 release of PMNs by platelets is TREM-1 dependent. Purified and fixed platelets were mixed with PMNs (ratio PLT/PMN, 30:1) and analyzed for respiratory burst (A,C) measured in a fluorescence reading device or IL-8 release by ELISA analysis (B,D), respectively. (A,C) Specific fluorescence index (SFI) of stimulated cells was obtained by subtraction of the background fluorescence of labeled cells incubated in medium alone. The enhancement of LPS-induced respiratory burst or IL-8 release of PMNs by platelets is neutralized by α–TREM-1 (clone 6B1) (A,B) or rsTREM-1 (C,D). Shown is the mean of triplicates of at least 3 experiments plus or minus SD after 125 minutes. Asterisks indicate statistically significant differences calculated by Student t test (P < .01).