Page 89 - Veterinary Immunology, 10th Edition

the prostacyclins are produced by vascular endothelial cells and the
VetBooks.ir thromboxanes come from platelets. The biological activities of the

prostaglandins vary widely, and since many different
prostaglandins are released in inflamed tissues, their net effect on

inflammation may be complex.
As neutrophils enter inflamed tissues, their 15-lipoxygenase
generates lipoxins from arachidonic acid. These oxidized
eicosanoids inhibit neutrophil migration. Thus, as inflammation

proceeds, there is a gradual switch in production from
proinflammatory leukotrienes to antiinflammatory lipoxins. The
rise in PGE in tissues also inhibits 5-lipoxygenase activity and
2
eventually suppresses inflammation.
Activated neutrophils, mast cells, platelets, and eosinophils also
produce a phospholipid called platelet-activating factor (PAF). PAF

makes endothelial cells even stickier and thus enhances neutrophil
adhesion and emigration. PAF aggregates platelets and makes them
release their vasoactive molecules and synthesize thromboxanes. It
acts on neutrophils in a similar fashion. Thus it promotes
neutrophil aggregation, degranulation, chemotaxis, and release of

oxidants.

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