Platelet-Activating Factor, PAF Acetylhydrolase, and Severe Anaphylaxis

Platelet-activating factor (PAF) is an anaphylactic mediator that is degraded in the blood by the enzyme PAF acetylhydrolase. In this study, patients with anaphylactic reactions were found to have higher levels of circulating PAF and lower levels of PAF acetylhydrolase activity than were patients without anaphylaxis. PAF-acetylhydrolase levels were low in patients who died as a result of an anaphylactic reaction to peanuts. Patients with anaphylactic reactions were found to have higher levels of circulating platelet-activating factor (PAF) and lower levels of PAF acetylhydrolase activity than were patients without anaphylaxis. Anaphylaxis is a rapid, potentially fatal, immediate hypersensitivity reaction characterized by laryngeal edema, bronchoconstriction, systemic hypotension, and vascular leakage. 1 Factors that predispose persons to anaphylaxis include age, atopy, asthma, mastocytosis, and activating mutations of mast cells. 2 – 4 Preformed and newly formed biochemical mediators, including histamine, tryptase, carboxypeptidase A, prostaglandin D 2 , leukotrienes, and platelet-activating factor (PAF), are released systemically during the degranulation of mast cells and basophils. 5 PAF is a proinflammatory phospholipid synthesized and secreted by mast cells, monocytes, and fixed tissue macrophages. 6 Circulating levels of PAF are, in part, controlled by the activity of PAF acetylhydrolase, which is . . .