Inborn errors of oxygen-dependent microbial killing by neutrophils.

The neutrophil granulocyte is a wandering blood and tissue cell which protects the host by ingestion and subsequent killing of invading microorganisms. It is extremely well equipped for this function. Its antimicrobial activity consists of three stages: chemotaxis, phagocytosis, and microbial destruction. The neutrophil first responds to the concentration gradient of chemical mediators activated in the vicinity of invading microorganisms and migrates toward their source (chemotaxis). Microorganisms coated with serum proteins are then identified as targets. These proteins, also called opsonins, consist of immunoglobulins and complement factors that are recognized by specific receptors on the phagocyte membrane. The neutrophil flows around the opsonized microorganisms. Invagination of the plasma membrane occurs with the incorporation of the organisms into intracellular vacuoles (phagocytosis, Fig. I a, b). Then neutrophil granules discharge their hydrolytic enzymes into the phagocytic vacuoles (degranulation) and microbicidal hydrogen peroxide is produced in an oxygen-consuming metabolic pathway. The end result is the death of the ingested organism, which is finally degraded.