Platelet-activating factor (PAF) and PAF acetylhydrolase have been identified as important mediators of anaphylaxis in humans, according to Canadian researcher Vadas and colleagues. PAF is a proinflammatory phospholipid secreted by mast cells, monocytes and fixed tissue macrophages; PAF acetylhydrolase is the enzyme that inactivates PAF. In a two-part study, they found that: (1) mean serum PAF levels were not only higher in 41 patients with anaphylaxis than in 23 healthy volunteers but were also correlated with the severity of anaphylaxis; and (2) that serum PAF acetylhydrolase activity was lower in nine patients with fatal peanut anaphylaxis than patients in any of several control groups. They suggested that failure of PAF acetylhydrolase to inactivate PAF may contribute to the severity of anaphylaxis.
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