The importance of hydrogen peroxide in phagocytic bactericidal activity of Japanese eel neutrophils

The bactericidal activity of Japanese eel neutrophils in the presence of oxygen radical scavengers was investigated. Catalase inhibited bacterial killing, while superoxide dismutase and hydroxyl radical scavengers (D-mannitol, sodium benzoate) did not. Superoxide dismutase had no synergetic effect with catalase. These observations indicate that hydrogen peroxide acts as a potent factor in the bactericidal process by eel neutrophils. The phagocytic index of cytochalasin B-treated neutrophils was less than one third of that of control neutrophils, although their phagocytic rate was more than 90%. Cytochalasin B, which inhibits phagosome formation without suppressing radical production, decreased the bactericidal activity of the neutrophils. and catalase did not affect the bacterial killing of cytochalasin B-treated neutrophils. Exposure to hydrogen peroxide at concentrations, which are expected within eel neutrophils during the respiratory burst, effectively killed the bacteria tested. Thus, it is suggested that the hydrogen peroxide-dependent bactericidal activity in eel neutrophils is expressed only within phagosomes but not extracellularly and that phagosome formation is essential for this activity.