Fig. 2.

N. gonorrhoeae actively inhibits the oxidative burst in HL-60 cells. Production of ROS was measured by LDCL over a period of 60 min. RLU, relative light units. (A) N. gonorrhoeae (Ngo) inhibits the oxidative burst induced by PMA. Differentiated HL-60 cells were either left unstimulated, were stimulated with 100 ng/ml PMA, were infected with piliated strain FA1090 at an MOI of 100, or were simultaneously infected and stimulated with PMA. The data are representative of 5 independent experiments. (B) N. gonorrhoeae inhibits the oxidative burst induced by opsonized S. aureus. Differentiated HL-60 cells were either left unstimulated or were infected with opsonized S. aureus at an MOI of 132 or coinfected with S. aureus and N. gonorrhoeae strain FA1090 at an MOI of 65. ROS production was measured over 60 min. Data are representative of 5 independent experiments. (C) Live bacteria are required to inhibit ROS production. HL-60 cells were treated with PMA and infected with either live, exponentially growing N. gonorrhoeae at an MOI of 108 or heat-killed bacteria (MOI < 1.7 × 10⁻⁶). The data are representative of 3 independent experiments. (D) ROS inhibition in HL-60 cells is not dependent on Opa expression. HL-60 cells were treated with PMA and infected with either piliated FA1090 bacteria that were Opa⁻ or an Opa⁻strain with OpaB expressed from an ectopic site at an MOI of 100 or 40, respectively. The data represent 4 independent experiments. (E) Inhibition of PMA-induced ROS production is not dependent on phagocytosis. HL-60 cells were pretreated with 10 μg/ml cytochalasin D for 5 to 10 min prior to addition of PMA and/or bacteria (MOI = 90). The data are representative of 4 independent experiments.