Lipoxin A4 is a trihydroxy fatty acid containing a conjugated tetraene, produced by the metabolism of 15-HETE or 15-HpETE with human leukocytes. Lipoxin A4 is equipotent to leukotriene B4 (LTB4) in inducing superoxide generation in human neutrophils at 0.1 µM. Lipoxin A4 is associated with several other biological functions including leukocyte activation, chemotaxis effects, natural killer cell inhibition (potent human PKC (protein kinase C) activator; inhibits cytotoxicity of natural killer cells), and monocyte migration and adhesion. Biosynthesis occurs in human leukocytes and rat alveolar macrophages. Transcellular biosynthesis occurs via interaction of human neutrophils or granulocytes and platelets. Produced in human nasal polyps and bronchial tissue. Stimulates vasodilation and antagonizes LTD4-induced vasoconstriction. Induces glomerular hyperperfusion and hyperfiltration. Inhibits LTB4- or FMLP-induced leukocyte chemotaxis and blocks the mobilization of Ca2+ and IP3. Inhibits LTB4-induced inflammation in the hamster cheek pouch. Activates protein kinase C13. Regulates human myelopoiesis. Lipoxin A4 is an activator of GPR.