Efficient T-cell priming and activation requires signaling through prostaglandin E2 (EP) receptors.

Understanding the regulation of T-cell responses during inflammation and auto-immunity is fundamental for designing efficient therapeutic strategies against immune diseases. In this regard, prostaglandin E₂ (PGE₂) is mostly considered a myeloid-derived immunosuppressive molecule. We describe for the first time that T cells secrete PGE₂ during T-cell receptor stimulation. In addition, we show that autocrine PGE₂ signaling through EP receptors is essential for optimal CD4⁺ T-cell activation in vitro and in vivo, and for T helper 1 (Th1) and regulatory T cell differentiation. PGE₂ was found to provide additive co-stimulatory signaling through AKT activation. Intravital multiphoton microscopy showed that triggering EP receptors in T cells is also essential for the stability of T cell--dendritic cell (DC) interactions and Th-cell accumulation in draining lymph nodes (LNs) during inflammation. We further demonstrated that blocking EP receptors in T cells during the initial phase of collagen-induced arthritis in mice resulted in a reduction of clinical arthritis. This could be attributable to defective T-cell activation, accompanied by a decline in activated and interferon-γ-producing CD4⁺ Th1 cells in draining LNs. In conclusion, we prove that T lymphocytes secret picomolar concentrations of PGE₂, which in turn provide additive co-stimulatory signaling, enabling T cells to attain a favorable activation threshold. PGE₂ signaling in T cells is also required for maintaining long and stable interactions with DCs within LNs. Blockade of EP receptors in vivo impairs T-cell activation and development of T cell-mediated inflammatory responses. This may have implications in various pathophysiological settings. [ABSTRACT FROM AUTHOR]