Inflammatory cytokines: sources and principal actions
THE CONTEXT
Cytokines coordinate systemic inflammatory responses, leukocyte recruitment, and macrophage activation. Their roles overlap between acute and chronic inflammation.
Cytokines associated with acute inflammation
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IL-1 is produced by macrophages, endothelial cells, and some epithelial cells. Its actions resemble those of TNF, with a greater role in fever.
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IL-6 is produced by macrophages and other cells and mediates systemic effects, including the acute-phase response.
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Chemokines are produced by macrophages, endothelial cells, T lymphocytes, mast cells, and other cell types. They recruit leukocytes to inflammatory sites and direct cell migration in healthy tissues.
Cytokines listed under chronic inflammation
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IL-12 from dendritic cells and macrophages increases production of interferon (IFN-g).
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IFN-g from T lymphocytes and natural killer cells activates macrophages, increasing their ability to kill microbes and tumor cells.
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IL-17 from T lymphocytes recruits neutrophils and monocytes.
Chemokine grouping and functional overlap
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Chemokines are divided into four groups according to the number of amino acids between two conserved cysteines. These groups have somewhat different target-cell specificities.
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The acute and chronic categories overlap considerably: all cytokines listed under acute inflammation may also contribute to chronic inflammatory reactions.