Box 9.2 Phagocytosis

Recognition and attachment

Phagocyte receptors recognize and bind to certain foreign molecular patterns and opsonins such as antibodies and complement components

Ingestion

Psuedopodia are extended around the foreign particle and enclose it within a “phagosome” (engulfment). The phagosome is pulled toward the center of the cell by polymerization of actin and myosin by microtubules

Killing and digestion

Oxygen dependent

Respiratory burst through the activation of NADPH oxidase. H2O2 and hypochlorite are produced.

Killing and digestion

Oxygen independent

The pH within the phagosome becomes alkaline and then neutral, the pH at which digestive enzymes work. Primary and secondary lysosomes (granules) fuse to the phagosome and empty hydrolytic enzymes and other bactericidal molecules into the phagosome.

Formation of neutrophil extracellular traps

Nuclear and organelle membranes dissolve, and activated cytoplasmic enzymes attach to DNA. The cytoplasmic membrane ruptures and DNA attached enzymes are expelled so that the bacteria is digested in the external environment