Prostaglandin E2 enhances Th17 responses via modulation of IL-17 and IFN-gamma production by memory CD4+ T cells.

The contribution of Th1 and Th17 cells in chronic inflammatory conditions leading to autoimmunity remains highly controversial. In inflamed tissues, production of prostaglandins by COX-2 has been proposed to favor Th17 responses indirectly by increasing IL-23 and blocking IL-12 release from APC. We report here that prostaglandin E2 (PGE2) can directly modulate cytokine production by human memory CD4(+) T cells. TCR triggering in the presence of PGE2 increased IL-17 and reduced IFN-gamma production by freshly isolated memory T cells or T-cell clones. PGE2 triggered the EP2 and EP4 receptors expressed on T cells leading to a rapid increase of retinoic-acid-related orphan receptor-gammat (ROR-gammat) and decrease of T-cell-specific T-box transcription factor 21 (T-bet) mRNA. Moreover, PGE2 promoted the selective enrichment of IL-17-producing cells by differentially modulating the proliferation of memory T-cell subsets in vitro. Taken together our results indicate that T-cell effector function is a direct target for PGE2 modulation and suggest a novel mechanism by which inhibitors of prostaglandin synthesis, such as COX-2 inhibitors, exert their anti-inflammatory effect.