The phosphodiesterase 4 inhibitor roflumilast augments the Th17-promoting capability of dendritic cells by enhancing IL-23 production, and impairs their T cell stimulatory activity due to elevated IL-10

• A clinically used PDE4 inhibitor enhances IL-23 production in dendritic cells.
• This results in elevated IL-17 production by cocultured allo-reactive T cells.
• Besides, production of the Th2 cytokines IL-5 and IL-10 is markedly reduced.
• In contrast, levels of IFN-γ are largely unaltered.
• Hence, PDE4 inhibitors as applied to suppress allergy may also favor Th17 responses.

Phosphodiesterase 4 (PDE4) inhibitors serve to prevent degradation of the intracellular second messenger cAMP, resulting in broad anti-inflammatory effects on different cell types including immune cells. Agents that elevate cAMP levels via activation of adenylate cyclase have been shown to imprint a Th17-promoting capacity in dendritic cells (DCs). Therefore, we studied the potential of therapeutically relevant PDE inhibitors to induce a pronounced Th17-skewing capacity in DCs. Here we show that mouse bone marrow-derived (BM-) DCs when treated with the PDE4 inhibitor roflumilast (ROF, trade name: Daxas) in the course of stimulation with LPS (ROF-DCs) evoked elevated IL-17 levels in cocultured allogeneic T cells. In addition, as compared with control settings, levels of IFN-γ remained unaltered, while contents of Th2 cytokines (IL-5, IL-10) were diminished. ROF enhanced expression of the Th17-promoting factor IL-23 in BM-DCs. In line, neutralizing antibodies specific for IL-23 or IL-6 when applied to DC/T cell cocultures partially inhibited the IL17-promoting effect of ROF-DCs. Furthermore, ROF-DCs displayed a markedly diminished allogeneic T cell stimulatory capacity due to enhanced production of IL-10, which was restored upon application of IL-10 specific neutralizing antibody to DC/T cell cocultures. Both the IL-17-inducing and impaired T cell stimulatory capacity of BM-DCs were mimicked by a specific activator of protein kinase A, while stimulation of EPACs (exchange proteins of activated cAMP) did not yield such effects. Taken together, our findings suggest that PDE4 inhibitors aside from their broad overall anti-inflammatory effects may enhance the Th17-polarizing capacity in DCs as an unwanted side effect.