Lymphatic responses and initial leukocyte recruitment
THE CONTEXT
Acute inflammation increases lymphatic drainage and recruits circulating leukocytes through a sequence of endothelial interactions and tissue migration.
Lymphatic drainage and inflammation
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Increased lymph flow helps drain edema fluid that accumulates because of increased vascular permeability.
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Secondary inflammation of lymphatics is called lymphangitis. It produces red streaks extending from an inflammatory focus along lymphatic channels.
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Draining lymph nodes may become enlarged because of increased cellularity and may be painful. These changes constitute reactive or inflammatory lymphadenitis.
Recruitment sequence
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Adhesion molecules and cytokines mediate and control leukocyte movement from the vessel lumen into tissue.
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The major phases are adhesion to endothelium at the inflammatory site, transmigration through the vessel wall, and movement toward the offending agent.
Margination, rolling, and firm adhesion
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During normal laminar flow from capillaries into postcapillary venules, centrally concentrated red cells displace leukocytes toward the vessel wall.
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As flow slows during early inflammation, leukocytes slow more than red cells because they are larger. Their increasingly peripheral position along the endothelial surface is called margination.
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Proximity to the vessel wall allows leukocytes to detect and respond to endothelial changes.
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Locally produced cytokines and other mediators activate endothelial cells to express adhesion molecules. Leukocytes attach loosely, repeatedly bind and detach, and tumble along the endothelial surface; this is rolling.
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After rolling, leukocytes eventually come to rest and adhere firmly.