Antimicrobial action of polymorphonuclear leukocytes depends on an array of substances carried in their cell membranes and cytoplasmic granules. These substances mediate killing in several systems. Some depend on molecular oxygen while others are independent of it. Some of the systems that depend on oxygen also require myeloperoxidase. The different systems seem able to act in primary or in reserve capacities backing each other up in times of stress or failure. Thus a deficiency in one system does not necessarily leave the polymorphs completely incapable of antimicrobial action although impairment may be severe as in chronic granulomatous disease. In general a poorly functioning polymorph is better than no polymorph at all.
