ABSTRACT
The immune system is a highly sophisticated and flexible defense system, designed by nature to protect the body against pathogenic organisms and any other cell, tissue, organ, or particle which is characterized as nonself. Phagocytes respond to stimulation with the activation of a transmembrane NADPH oxidase on the cytoplasmic side of the membrane which reduces oxygen in the extracellular fluid, or in the phagosome when the membrane is invaginated. Phagocytes internalize foreign material by invagination of their cell membrane and formation of a phagosome. Secretion of oxygen radicals and enzymes into the phagosome results in the killing of engulfed microorganisms and degradation of the ingested organic material. The role of the ascorbic acid system in the microbicidal activity of intact leukocytes is only incompletely understood. The level of this vitamin rapidly decreases in leukocytes following a viral infection, and returns to normal after recovery.
