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Polymorphonuclear leukocytes

المؤلف:  Patrick R. Murray, Ken S. Rosenthal, and Michael A. Pfaller

المصدر:  Medical Microbiology (2026)

الجزء والصفحة:  10th E ,P 42-43

2026-11-12

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Polymorphonuclear leukocytes (neutrophils) are short-lived cells that constitute 50% to 70% of circulating white blood cells and are the primary phagocytic defense against bacterial and fungal infection and a major component of the inflammatory response. Neutrophils are 9 to 14 μm in diameter, lack mitochondria, have a granulated cytoplasm in which granules stain with both acidic and basic stains, and have a multilobed nucleus. Neutrophils leave the blood and concentrate at the site of infection in response to chemotactic factors. During infection, the neutrophils are recruited from the bone mar row to increase the numbers in blood and these will include precursor forms. These precursors are termed band forms, which is in contrast to the terminally differentiated and segmented neutrophils (segs). The finding of such an increase in precursor neutrophils by a blood count is sometimes termed a left shift with an increase in bands versus segs. Neutrophils ingest bacteria by phagocytosis and expose the bacteria to antibacterial substances and enzymes contained in primary (azurophilic) and secondary (specific) granules. Primary granules are reservoirs for enzymes such as myeloperoxidase, β-glucuronidase, elastase, and cathepsin G. Specific granules serve as reservoirs for lysozyme and lactoferrin. Dead neutrophils release a sticky antimicrobial net of deoxyribonucleic acid (DNA) and other fibers, termed neutrophil extracellular trap (NET), and dead neutrophils are the major component of pus.

Eosinophils are heavily granulated cells (11–15 μm in diameter) with a bilobed nucleus that stain with the acid dye eosin Y. They are also phagocytic, motile, and granulated. The granules contain acid phosphatase, peroxidase, and eosinophilic basic proteins. Eosinophils play a role in the defense against parasitic infections. The eosinophilic basic proteins are toxic to many parasites. Mast cells and basophils are nonphagocytic granulocytes that release the contents of their granules in response to inflammatory triggers and during allergic responses (type 1 hypersensitivity). Mast cells also release histamine when activated that cause leakage of fluid from capillaries.