Phagocytic cells in host defence.

The normal response of phagocytic cells to microbial invasion may be divided into three interrelated phases: the recognition and migration of the phagocytes to the site of infection, the phagocytosis or ingestion of the microorganisms and the cellular and metabolic factors involved in the killing of the microorganisms. A wide spectrum of clinical disorders, characterized by enhanced susceptibility to infection, has been related to defects in any of these functions. Furthermore, for every step of phagocyte response to infection, a mechanism seems to exist by which the microorganisms can avoid the injurious consequences of their interactions with normal phagocytes. The interactions between normal and defective phagocytes and microorganisms are presented.