Microbe ingestion and killing by neutrophils: normal mechanisms and abnormalities

Microbial ingestion and killing by neutrophils involves the interaction between the phagocytic cells of the body and certain serum factors. The primary phagocytes of the blood are the polymorphonuclear neutrophil, eosinophil and monocyte. The fixed tissue macrophage of the reticuloendothelial system is responsible for phagocytosis and killing of encapsulated bacteria, viruses, and protozoans, whereas the blood phagocyte system is involved in killing of pyogenic bacteria and certain fungi. Proper ingestion of bacteria requires opsonisation of these bacteria by either complement of specific antibody, or an interaction of these two proteins. Opsonised bacteria are fixed to the surface of the phagocytic cells which contain receptors for IgG and C3. Following immune adherence ingestion of bacteria involves invagination of the plasmalemmal membrane. This process utilises ATP and a re-arrangement of lipids occurs during formation of the phagocytic vacuole. Granular enzymes containing peroxidase, hydrolases, and cationic proteins are transferred from the granule into the phagocytic vacuole. There is activation of oxidative metabolism with an increased consumption of oxygen leading to hydrogen peroxide production.