Analysis of the activation steady-state of U937 and RU clones. (A) O⁻_2^⋅ production was quantitated by measuring the reduction of NBT, after incubation of the cultures (5 × 10⁵ cells/mL) for 5 hours in RPMI supplemented with 10% FCS in the presence () or absence (▪) of 500 IU/mL of human SOD. (B) NO production was determined by quantitating NO⁻₂/NO⁻₃ in supernatants of cultures (2 × 10⁵ cells/mL) incubated for 36 hours in complete medium in the presence (□) or absence (▪) of 0.5 mmol/L L-NMA. Average values from triplicates cultures are shown with standard derivatives bars.