The phagocytic system in host defense.

In response to microbial invasion, an inflammatory response is stimulated, polymorphonuclear cells accumulate, and the infection is localized. Active factors released by microbes or from activation of complement attract neutrophils in a unidirectional fashion toward the highest concentration of factors in the center of an inflammatory process. Opsonins increase the affinity of microbes for phagocytic cells by neutralizing antiphagocytic factors on the microbial surface and binding to the surface of phagocytes. Enzymes responsible for the respiratory oxidative metabolism during phagocytosis reside in the neutrophil plasma membrane. Perturbation of membrane receptors stimulate the metabolic machinery required for engulfment of particles and for oxidative metabolism of the phagocytic cell. Highly reactive oxygen radicals, superoxide and singlet oxygen, and hydrogen peroxide are produced during the oxidative response to phagocytosis. These and factors released from azurophilic and specific granules are critical factors determining microbial death within phagocytic vacuoles.