LPS-induced respiratory burst of PMNs is enhanced in the presence of platelets. Purified and fixed platelets were mixed with PMNs, which were incubated with DCFH-DA (ratio PLT/PMN, 30:1), and respiratory burst was measured in a fluorescence reading device. Shown is the mean of doublets of at least 3 experiments ± SD after 125 minutes. Specific fluorescence index (SFI) of stimulated cells was obtained by subtraction of the background fluorescence of labeled cells incubated in medium alone. Platelets (□) enhance the LPS-induced respiratory burst of PMNs in contrast to neutrophils alone (■). Platelets have no effect on the respiratory burst of unstimulated PMNs. Respiratory burst is enhanced when platelets are preincubated with thrombin (▒). Asterisks indicate statistically significant differences calculated by Student t test (P < .01).