Indomethacin sensitizes resistant transformed cells to macrophage cytotoxicity

•Resistant tumor cells secrete a suppression factor that prevents the tumoricidal activities of LPS-stimulated macrophages.•The suppression factor was identified as Prostaglandin E2 (PGE2).•High concentrations of PGE2 prevented TNFα secretion by LPS-stimulated macrophages, while low concentrations were stimulatory.•Prevention of PGE2 production by Indomethacin sensitized resistant tumor cells to macrophage cytotoxicity.