Platelet-activating factor (β-Acetyl-γ-O-alkyl-L-α-phosphatidylcholine, or PAF) is a phospholipid that mediates many leukocyte functions. Stimulates platelet aggregation and has roles in inflammation, anaphylaxis and wound repair. Produced by lymphocytes, platelets, and endothelial cells, and is also found to be secreted by tumor cells.