Resolution of inflammation is an important hallmark in the course of infectious diseases. Dysregulated inflammatory responses may have detrimental consequences for the affected organism. Therefore, tight regulation of inflammation is indispensable. Among numerous modulatory signaling pathways, the PI3K/PTEN signaling pathway has been proposed recently to be involved in the regulation of innate immune reactions. Here, we attempted to elucidate molecular mechanisms that contribute to the modulatory properties of the PI3K signaling pathway in inflammation. PTEN-deficient macrophages, which harbor constitutively active PI3Ks, were analyzed in response to gram-negative bacteria and PAMPs such as LPS. PTEN-deficient cells showed reduced inflammatory cytokine production, which was accompanied by reduced MAPK signaling activation in early- as well as late-phase activation. Simultaneously, we found increased levels of the MKP DUSP1, as well as the anti-inflammatory cytokine IL-10. Our data suggest that differential DUSP1 regulation coupled with enhanced IL-10 production contributes to the anti-inflammatory properties of the PI3K pathway.

Immunosuppressive cytotoxic T lymphocyte associated antigen-4 immunoglobulin fusion proteins (CTLA4-Ig) block the CD28:CD80/86 costimulatory pathway. On a cellular level, CTLA4-Ig is understood to dampen T cell responses. As a mechanism, CTLA4-Ig has been reported to affect dendritic cell (DC) function via inducing the immunosuppressive indoleamine 2,3 dioxygenase (IDO) pathway and promoting a DC regulatory phenotype. We here probed cellular mechanisms of CTLA4-Ig immunoregulation in an allogeneic setting using C57BL/6 splenic or bone marrow derived DCs (BMDCs) as stimulators of allogeneic Balb/c derived T cells. To address whether CTLA4-Ig immunosuppression affected DCs, we pre-exposed C57BL/6 splenic or BMDCs to CTLA4-Ig and removed unbound CTLA4-Ig before co-culture with allogeneic T cells. CTLA4-Ig disappeared rapidly (within 4 h) from the cell membrane by combined internalization and dissociation. These CTLA4-Ig pre-exposed DCs were fully capable of stimulating allogeneic T cell proliferation, suggesting that CTLA4-Ig does not impair the DC stimulatory capacity. Only the presence of CTLA4-Ig during DC/T cell co-culture resulted in the expected inhibition of proliferation. C57BL/6 splenic or BMDCs exposed to CTLA4-Ig did not display IDO activity. We conclude that CTLA4-Ig immunosuppressive activity does not depend on a DC regulatory phenotype but on its presence during DC/T cell interaction.

The chemical synthesis and biological activity of novel functionalized imidazoquinoline derivatives (ImQ) to generate Toll‐like receptor (TLR) 7/8 specific prodrugs are presented. In vivo activity of ImQs to induce inflammation was confirmed in zebrafish larvae. After covalent ligation to fully biodegradable polyphosphazenes (ImQ‐polymer), the macromolecular prodrugs were designed to undergo intracellular pH‐sensitive release of ImQs to induce inflammation through binding to endosomal TLR7/8 (danger signal). We showed ImQ dissociation from prodrugs at a pH 5 pointing towards endosomal prodrug degradability. ImQ‐polymers strongly activated ovalbumin‐specific T cells in murine splenocytes as shown by increased proliferation and expression of the IL‐2 receptor (CD25) on CD8+ T cells accompanied by strong IFN‐γ release. ImQ prodrugs presented here are suggested to form the basis of novel nanovaccines, for example, for intravenous or intratumoral cancer immunotherapeutic applications to trigger physiological antitumor immune responses.

Prostaglandin E2 (PGE 2 ), an abundantly produced lipid messenger in mammalian organisms, has been attributed to possess potent albeit ambivalent immunological functions. Recently, PGE 2 has been reported to stimulate the commonly believed immunosuppressive indoleamine 2,3-dioxygenase (IDO) pathway in human dendritic cells (DCs), but without promoting DC immunosuppressive activity. Here, we report that PGE 2 used as a DC maturation agent apparently has more diverse functions. PGE 2 -matured DCs acquired powerful IDO activity, which was sustained even after removing PGE 2 . These IDO-competent DCs were able to stimulate allogeneic T-cell proliferation, but achieved inhibitory activity as their content in DC/T-cell co-cultures increased. The DC inhibitory activity was reversed upon blockade of IDO activity, confirming that the suppressive effect was in fact mediated by IDO and occurred in a dose-dependent fashion. IDO-mediated T-cell suppression was restored upon re-stimulation of T cells in the absence of IDO activity, confirming its reversibility. T cells stimulated by PGE 2 -matured IDO-competent DCs were sensitized to produce multiple cytokines, comprising Th1, Th2, and Th17 phenotypes. Collectively, these data suggest that T cells stimulated by PGE 2 -matured DCs are not terminally differentiated and their ultimate type of response may be formed by microenvironmental conditions. Keywords: Human dendritic cells r IL-23 r Immunosuppression r Indoleamine 2,3-dioxygenase (IDO) r Prostaglandin E2 Supporting Information available online IntroductionThe intracellular enzyme indoleamine 2,3-dioxygenase (IDO) has a key function in tryptophan metabolism along the kynurenine pathway [1]. IDO's metabolic activity has been perceived to play a significant role in immune regulation. On the cellular level, the complementary effects of IDO-mediated metabolism, tryptophan starvation, and accumulation of immunomodulatory kynurenines Correspondence: Dr. Andreas Heitger e-mail: andreas.heitger@ccri.at at the antigen-presenting cell (APC)/T-cell synapse were proposed to effect regulation of T-cell activation and proliferation [1,2]. In fact, in the last decade, multiple studies corroborated the role of IDO in immune regulation and induction of tolerance (reviewed in [3,4]). IDO competence, i.e. IDO expression and activity [5,6], has been suggested to play a critical role in numerous clinical conditions entailing immune regulation, including tolerance induction in pregnancy [7], transplantation [8,9], and tumor immune evasion [10]. * These authors contributed equally to the work. Eur. J. Immunol. 2012Immunol. . 42: 1117Immunol. -1128 Effective induction of IDO competence is, by and large, restricted to cells of the monocyte/macrophage lineage and, in humans is predominantly found in dendritic cells (DCs) [4,11]. Numerous agents, most prominently interferon (IFN)-γ, have been described to induce IDO activity in DCs [12]. IDO induction is generally believed to represent a feedback mechanism of APC activation [8]. This understanding...

Gangliosides shed by tumors into their microenvironment (TME) are immunoinhibitory. Interferon-γ (IFN-γ) may boost antitumor immune responses. Thus we wondered whether IFN-γ would counteract tumor ganglioside-mediated immune suppression. To test this hypothesis, we exposed human monocyte-derived LPS-activated dendritic cells (DC) to IFN-γ and to a highly purified ganglioside, GD1a. DC ganglioside exposure decreased TLR-dependent p38 signaling, explaining the previously observed ganglioside-induced down-modulation of pro-inflammatory surface markers and cytokines. Strikingly, while increasing LPS-dependent DC responses, IFN-γ unexpectedly did not counteract the inhibitory effects of GD1a. Rather, induction of indoleamine 2,3-dioxygenase (IDO1), and expression of STAT1/IRF-1 and programmed cell death ligand (PD-L1), indicated that the immunoinhibitory, not an immune stimulatory, IFN-γ-signaling axis, was active. The combination, IFN-γ and DC ganglioside enrichment, markedly impaired DC stimulatory potential of CD8 T-cells. We suggest that gangliosides and IFN-γ may act in concert as immunosuppressive mediators in the TME, possibly promoting tumor progression.