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Neutrophils
The Phagocytic Inflammatory Response
The phagocyte system includes both granulocytes (neutrophils, eosinophils, and basophils) and mononuclear phagocytes (monocytes and tissue macrophages). Neutrophils and mononuclear phagocytes share primary functions, including the defining properties of large-particle ingestion and microbial killing. Phagocytes participate primarily in the innate immune response but also help initiate acquired immunity. Mononuclear phagocytes, including tissue macrophages and circulating monocytes, are discussed in Chapter 154 .
Neutrophils provide the rapid effector arm of the innate immune system. They circulate in the bloodstream for only about 6 hr ( Table 153.1 ), but on encountering specific chemotactic signals, they adhere to the vascular endothelium and transmigrate into tissues. There they ingest and kill microbes and release chemotactic signals to recruit more neutrophils and to attract dendritic cells and other initiators of the acquired immune response.
Table 153.1
Neutrophil and Monocyte Kinetics
From Boxer LA: Function of neutrophils and mononuclear phagocytes. In Bennett JC, Plum F, editors: Cecil textbook of internal medicine, ed 20, Philadelphia, 1996, Saunders.
| NEUTROPHILS | |
| Average time in mitosis (myeloblast to myelocyte) | 7-9 days |
| Average time in postmitosis and storage (metamyelocyte to neutrophil) | 3-7 days |
| Average half-life in the circulation | 6 hr |
| Average total body pool | 6.5 × 10 8 cells/kg |
| Average circulating pool | 3.2 × 10 8 cells/kg |
| Average marginating pool | 3.3 × 10 8 cells/kg |
| Average daily turnover rate | 1.8 × 10 8 cells/kg |
| MONONUCLEAR PHAGOCYTES | |
| Average time in mitosis | 30-48 hr |
| Average half-life in the circulation | 36-104 hr |
| Average circulating pool (monocytes) | 1.8 × 10 7 cells/kg |
| Average daily turnover rate | 1.8 × 10 9 cells/kg |
| Average survival in tissues (macrophages) | Months |
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