Involves the activation of the phagocyte NADPH oxidase complex (eg, in neutrophils, monocytes), which utilizes O₂ as a substrate.Plays and important role in the immune response → rapid release of reactive oxygen species (ROS). - NADPH plays a role in both the creation and neutralization of ROS. - Myeloperoxidase contains a blue-green heme-containing pigment that gives sputum its color.

Phagocytes of patients with CGD lack superoxide dismutase and cannot make H₂O₂ from O₂. They can utilize H₂O₂ generated by invading organisms and convert it to ROS. Patients are at ↑ risk for infection by catalase ⊕ species (eg, S aureus, Aspergillus) capable of neutralizing their own H₂O₂, leaving phagocytes without ROS for fighting infections.

Pyocyanin of P aeruginosa generates ROS to kill competing pathogens. Oxidative bust also leads to K⁺ influx, which releases lysosymal enzymes from proteoglycans. Lactoferrin is a protein found in secretory fluids and neutrophils that inhibits microbial growth via iron chelation.