PTGS2 and infection: After activation by infection, tissue damage, or exposure to endotoxin (i.e., lipopolysaccharides (LPS)), macrophages secrete a large amount of proinflammatory mediators, including inducible nitric oxide synthase (iNOS), nitric oxide (NO), cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6).