Prostaglandin E2 requirement for transforming growth factor β2 inhibition of elicited macrophage 14 kDa phospholipase A2 release

Abstract

1. Cultured elicited-peritoneal macrophages release a soluble type II 14 kDa phospholipase A2 (PLA2) over time, reaching a plateau by 20-24 h of incubation and maintaining these levels over 72 h. Prostaglandin E2 (PGE2) is also produced but does not plateau until 48-72 h. 2. Transforming growth factor beta 1 (TGF beta 1) reduces cellular 14 kDa PLA2 and its subsequent release by approximately half, but does not alter PGE2 production. Co-incubation of TGF beta 1 with indomethacin interfered, in a concentration-dependent manner, with the ability of TGF beta 1 to reduce cellular 14 kDa PLA2 and its subsequent release over 24 h. The regulation of TGF beta 1 was not specific to indomethacin since other non-steroidal anti-inflammatory drugs had the same effect. This suggested that cyclooxygenase activity was essential for TGF beta 1 to exert its effect and indeed, the addition of exogenous PGE2 restored the TGF beta 1 action. 3. PGE2 alone exerted a concentration-dependent negative feedback action on elicited-macrophage 14 kDa PLA2 release. The inhibitory concentration (IC50 = approximately 180 ng PGE2 ml-1) approximated the PGE2 levels measured in the 24 h macrophage conditioned media (85-140 ng PGE2 ml-1) where PLA2 release began to plateau. Further, incubation of cells with indomethacin over 48 h resulted in the enhancement of 14 kDa PLA2 activity compared to that released from untreated cells. Forskolin failed to inhibit 14 kDa PLA2 release, suggesting PGE2 was not acting through an increase in adenylate cyclase. 4. Taken together, the data are consistent with the immunosuppressive aspects reported for both mediators during inflammation and demonstrates the requirement of PGE2 for TGF beta 1 action on the elicited macrophage.