Leukocyte killing, inflammatory mediators, and morphologic patterns
THE CONTEXT
Leukocytes eliminate microbes and debris using mechanisms that can also injure normal tissue. Inflammatory mediators coordinate these responses, which produce recognizable morphologic patterns.
Elimination of microbes and tissue injury
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Leukocytes phagocytose microbes and dead cell debris, followed by destruction in phagolysosomes.
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Free radicals, including ROS and NO, generated in activated leukocytes and granule enzymes mediate destruction.
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Neutrophils can extrude nuclear contents to form extracellular nets that trap and destroy microbes.
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Extracellular release of enzymes and ROS can injure tissue. Thus, mechanisms that eliminate microbes and debris can also damage normal tissues.
Major inflammatory mediators
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Vasoactive amines, mainly histamine, cause vasodilation and increased vascular permeability.
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Arachidonic acid metabolites, including prostaglandins and leukotrienes, participate in vascular reactions, leukocyte chemotaxis, and other inflammatory reactions; lipoxins antagonize their effects.
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Cytokines are proteins produced by many cell types and usually act over short distances. In inflammation, their major roles include leukocyte recruitment and migration; principal acute inflammatory cytokines include TNF, IL-1, and chemokines.
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Microbes or antibodies activate complement, generating products responsible for leukocyte chemotaxis, opsonization, phagocytosis of microbes and other particles, and cell killing.
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Kinins arise through proteolytic cleavage of precursors and mediate vascular reactions and pain.
Morphologic patterns
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Serous inflammation consists of protein-rich exudate accumulating in body cavities and spaces created by tissue necrosis.
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Fibrinous inflammation involves fibrin formation, usually on organ surfaces such as the heart and lungs.
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Purulent inflammation produces pus containing dead cells, neutrophils, and microbes and is most often caused by bacterial infection. An abscess is localized purulent inflammation.
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An ulcer is an epithelial discontinuity with underlying acute and chronic inflammation.