What is Phagocytosis and the respiratory burst?

A phagocyte binds its prey through receptors for opsonins — C3b, and the constant regions of antibodies — or directly through pattern receptors, wraps it in membrane, and closes the phagosome, which fuses with granules and lysosomes. Killing is by several means at once. The respiratory burst: the enzyme NADPH oxidase, assembled on the phagosome membrane, pumps electrons onto oxygen to make superoxide, which becomes hydrogen peroxide, which myeloperoxidase turns, with chloride, into hypochlorite — bleach, at millimolar concentration inside a compartment a micrometre across. Nitric oxide from inducible NO synthase, which with superoxide gives peroxynitrite. Acid, to pH 5. Lysozyme, proteases, lactoferrin that starves the prey of iron, and defensins that puncture it. A neutrophil that cannot eat what it finds — a fungal hypha, a clump — can expel its own chromatin as a sticky net of DNA and granule proteins, a neutrophil extracellular trap, and die doing it. Children who inherit a defective NADPH oxidase (chronic granulomatous disease) suffer recurrent abscesses and granulomas from bacteria and fungi that ordinary phagocytes kill without difficulty: the burst is not optional.