TLR stimulation primes superoxide generation. (A) Human neutrophils were stimulated for 1 hour in the presence of cytochrome c, with or without 90 minutes of pretreatment with GM-CSF. Superoxide generation was determined by measuring SOD-inhibitable change in absorbance at 550 nm. (B) Human neutrophils were isolated and stimulated for 1 hour in the presence of cytochrome c. The cells were further stimulated with 0.1 μM fMLF for 15 minutes and superoxide generation determined as above. *P < .1, **P < .05, as determined by Student t test, compared with cells treated with fMLF alone. Error bars indicate standard deviation of triplicate measurements. Data are representative of 3 similar experiments conducted on 2 donors.