Cyclooxygenase-2 dependent prostaglandin E2 signaling through the EP3 receptor is required for cell-mediated immunity to Listeria monocytogenes

Abstract

Abstract The bacterial pathogen Listeria monocytogenes (Lm) is being developed as a cancer immunotherapeutic platform due to its ability to elicit robust CD8+ T cell responses. Though the role of cytokines in Lm-stimulated immunity is well studied, the role of eicosanoids, lipid modulators of inflammation, is unclear. We previously demonstrated that cyclooxygenase-2 (COX-2) dependent prostaglandin E2 (PGE2) is essential for optimal T-cell priming. Antigen specific T cells and protective immunity were decreased following either treatment with the COX-2 inhibitor celecoxib or immunization of mice deficient in microsomal PGE2 synthase-1. Analysis of splenic eicosanoid levels revealed an upregulation of PGE2 twelve hours post immunization and administration of exogenous PGE2 at this time restored immunity during COX-2 inhibition. To understand how PGE2 impacts T-cell priming we assessed the role of the receptors EP1–4 in mediating this response using small molecule agonists and antagonists. EP3 blockade impaired immune responses while the use of an EP3 specific agonist restored immunity during COX-2 inhibition, suggesting that PGE2 signaling through EP3 is critical for T-cell priming. Conversely, consistent with its predicted inverse role in cAMP signaling, EP4 blockade enhanced responses, providing a mechanism by which to improve Listeria-based immunotherapeutics. Ongoing studies with floxed COX-2, EP3 and EP4 mice will illuminate the cell types producing and responding to PGE2. In conclusion, PGE2 signaling through EP3 is necessary Lm-stimulated immunity while EP4 signaling is detrimental. Further understanding these signaling pathways and where they function will be key to optimizing Lm as therapeutic platform.