Effects of oxygen tension and pH on the respiratory burst of human neutrophils

The respiratory burst of human neutrophils was measured under conditions of hypoxia and low pH. O₂^- production by neutrophils activated with opsonized zymosan fell slowly as the oxygen concentration declined to 1%, then dropped more sharply, reaching negligible levels at oxygen concentrations less than 0.25%. Production was half maximal at an oxygen concentration of 0.35% (equivalent to ~ 10-μM dissolved oxygen). O₂^- production by the cell-free O₂^--forming system prepared from zymosan-activated neutrophils showed a similar dependence on oxygen concentration. A drop in pH caused decreases in both oxygen consumption and O₂^- production by zymosan-treated neutrophils, values at pH 6.0 being 10%-20% of those observed at pH 7.5. Experiments with the cell-free O₂^--forming system suggested that this decline in respiratory burst activity at low pH was due to inefficient activation of the O₂^--forming enzyme under acidic conditions.