The enzymes 15-lipoxygenase -1 (15-LO-1 or ALOX15 ) and 15-lipoxygenase-2 (15-LO-2, ALOX15B ) metabolize arachidonic acid to the S stereoisomer of 15-Hydroperoxyeicosatetraenoic acid (15(S)-HPETE) which is rapidly reduced by cellular peroxidases to the S stereoisomer of 15-Hydroxyicosatetraenoic acid (15(S)-HETE).   The 15-lipoxygenases (particularly ALOX15) may also act in series with 5-lipoxygenase, 12-lipoxygenase, or aspirin-treated COX2 to form the lipoxins and epi-lipoxins or with P450 oxygenases or aspirin-treated COX2 to form Resolvin E3 (see Specialized pro-resolving mediators#EPA-derived resolvins .
Cells tend to secrete either LTB 4 or LTC 4 , though a few secrete comparable amounts of each. 5 Activated neutrophils secrete LTB 4 , which is an inducer of neutrophil chemotaxis, of neutrophil degranulation and of neutrophil-endothelial cell adhesion. 2, 5 LTC 4 , D 4 and E 4 , the "slow reactive substances of anaphylaxis", induce smooth-muscle contraction, increase vascular permeability to proinflammatory cells and enhance mucous secretion in the airways. 2, 5 In addition, both types of leukotrienes modulate the cytokine regulation of the immune system. Leukotrienes, like prostaglandins, act through G-protein-coupled, seven-transmembrane receptors. 1, 5