Functional differences between neutrophils and macrophages
THE CONTEXT
Neutrophils and macrophages share phagocytosis, migration into tissues, and chemotaxis, but differ in origin, longevity, and responses to activation.
Origin and tissue lifespan
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Neutrophils and macrophages recruited during inflammatory reactions originate from hematopoietic stem cells in bone marrow.
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Some tissue-resident macrophages originate from stem cells in the yolk sac or fetal liver during early development.
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Neutrophils survive in tissues for 1–2 days. Inflammatory macrophages survive for days or weeks, whereas tissue-resident macrophages can survive for years.
Activation and antimicrobial responses
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Neutrophil responses are rapid and short lived, relying mainly on degranulation and enzymatic activity. Macrophage responses are slower and more prolonged, often depending on new gene transcription.
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Neutrophil reactive oxygen species production is rapidly induced by assembly of phagocyte oxidase during the respiratory burst; this response is less prominent in macrophages.
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Neutrophils produce little or no nitric oxide. Macrophage nitric oxide production is induced following transcriptional activation of inducible nitric oxide synthase.
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Degranulation is a major neutrophil response induced by cytoskeletal rearrangement and is not prominent in macrophages.
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Cytokine production is low or absent in neutrophils but is a major macrophage function requiring transcriptional activation of cytokine genes.
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Neutrophil extracellular trap formation is rapidly induced by extrusion of nuclear contents; macrophages show little or none.
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Lysosomal enzyme secretion is prominent in neutrophils and less prominent in macrophages.
Shared functions and receptor activation
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Both cell types can phagocytose material, migrate through blood vessels into tissues, and undergo chemotaxis.
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Leukocyte surface receptors recognize different agonists and initiate responses that mediate leukocyte functions.
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Lipopolysaccharide first binds a circulating lipopolysaccharide-binding protein.