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(Pediatrics in Review. 1997;18:351-356.)
© 1997 American Academy of Pediatrics
| Introduction |
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These defenses consist first of a phylogenetically more primitive innate system that is provided primarily by phagocytic cells and acts as a first-line defense against many bacterial pathogens. The complement system amplifies the innate immune response by providing critical factors that enhance phagocytosis (opsonins) and attract cells to the site of inflammation (chemoattractants). The more recently acquired defense pathway, the adaptive immune system, involves a highly specific immune response to foreign substances (antigens) that includes lymphocytes. This chain of events is initiated by lymphocyte binding antigen and consists of cell-cell interactions and the release of numerous humoral mediators, including immunoglobulins and potent bioactive hormones called cytokines.
The division of labor within these various arms of the immune system is carried out by specific cell types. The two primary players are neutrophils and macrophages. Neutrophils are mobile phagocytes that migrate to sites of inflammation where they ingest and destroy microorganisms. The macrophage is a fixed tissue cell, found throughout the lymphoid and mucosal tissues, that provides critical phagocytic function for clearing antigenic substances from the circulation. The ingestion of foreign antigens by both cell types is enhanced in the presence of antibody and complement bound to the antigen.
The adaptive immune
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