The 5-lipoxygenase (5-LO) pathway generates lipid mediators, i.e. the cysteinyl leukotrienes (cysLTs) LTC 4 /LTD 4 and LTB 4 . CysLT receptors are expressed in endothelial cells (EC) and EC cysLT 2 -R activation induces diverse pro-inflammatory genes in vitro. We now report that LTD 4 promotes formation of an atherosclerosis-protective and anti-thrombotic eicosanoid by markedly up-regulating EC cyclooxygenase-2 (COX-2). CysLT-induced COX-2 transcripts were transiently up-regulated as determined by microarray and QRT-PCR analyses though COX-2 protein remained elevated for several hours. Prostacyclin formation, measured as its stable metabolite 6-keto-PGF 1α , was increased several fold in LTD 4 -stimulated ECs, and was inhibited by the COX-2-specific inhibitor, NS-398. COX-2 up-regulation was Ca 2+ -dependent and was partially blocked by cyclosporin A indicating that the 5-LO/COX-2 cross-talk involved signaling through a nuclear factor of activated T cells (NFAT) dependent pathway. Since prostacyclin is a major blood vessel-protective and anti-thrombotic eicosanoid, the EC cysLT 2 -R may limit its otherwise pro-inflammatory actions through a protective Ca 2+ /calcineurin/NFAT-dependent COX-2 feedback loop.