ngqian Li

Cutting Edge: DNA Sensing via the STING Adaptor in Myeloid Dendritic Cells Induces Potent Tolerogenic Responses

Cytosolic DNA sensing via the stimulator of IFN genes (STING) adaptor incites autoimmunity by inducing type I IFN (IFN-αβ). In this study, we show that DNA is also sensed via STING to suppress immunity by inducing IDO. STING gene ablation abolished IFN-αβ and IDO induction by dendritic cells (DCs) after DNA nanoparticle (DNP) treatment. Marginal zone macrophages, some DCs, and myeloid cells ingested DNPs, but CD11b+ DCs were the only cells to express IFN-β, whereas CD11b+ non-DCs were major IL-1β producers. STING ablation also abolished DNP-induced regulatory responses by DCs and regulatory T cells, and hallmark regulatory responses to apoptotic cells were also abrogated. Moreover, systemic cyclic diguanylate monophosphate treatment to activate STING induced selective IFN-β expression by CD11b+ DCs and suppressed Th1 responses to immunization. Thus, previously unrecognized functional diversity among physiologic innate immune cells regarding DNA sensing via STING is pivotal in driving immune responses to DNA.

Engineering DNA nanoparticles as immunomodulatory reagents that activate regulatory T cells

Nanoparticles containing DNA complexed with the cationic polymer polyethylenimine are efficient vehicles to transduce DNA into cells and organisms. DNA/polyethylenimine nanoparticles (DNPs) also elicit rapid and systemic release of proinflammatory cytokines that promote antitumor immunity. In this study, we report that DNPs possess previously unrecognized immunomodulatory attributes due to rapid upregulation of IDO enzyme activity in lymphoid tissues of mice. IDO induction in response to DNP treatment caused dendritic cells and regulatory T cells (Tregs) to acquire potent regulatory phenotypes. As expected, DNP treatment stimulated rapid increase in serum levels of IFN type I (IFN-αβ) and II (IFN-γ), which are both potent IDO inducers. IDO-mediated Treg activation was dependent on IFN type I receptor signaling, whereas IFN-γ receptor signaling was not essential for this response. Moreover, systemic IFN-γ release was caused by TLR9-dependent activation of NK cells, whereas TLR9 signaling was not required for IFN-αβ release. Accordingly, DNPs lacking immunostimulatory TLR9 ligands in DNA stimulated IFN-αβ production, induced IDO, and promoted regulatory outcomes, but did not stimulate potentially toxic, systemic release of IFN-γ. DNP treatment to induce IDO and activate Tregs blocked Ag-specific T cell responses elicited in vivo following immunization and suppressed joint pathology in a model of immune-mediated arthritis. Thus, DNPs lacking TLR9 ligands may be safe and effective reagents to protect healthy tissues from immune-mediated destruction in clinical hyperimmune syndromes.

Activation of the STING Adaptor Attenuates Experimental Autoimmune Encephalitis

Cytosolic DNA sensing activates the stimulator of IFN genes (STING) adaptor to induce IFN type I (IFN-αβ) production. Constitutive DNA sensing to induce sustained STING activation incites tolerance breakdown, leading to autoimmunity. In this study, we show that systemic treatments with DNA nanoparticles (DNPs) induced potent immune regulatory responses via STING signaling that suppressed experimental autoimmune encephalitis (EAE) when administered to mice after immunization with myelin oligodendrocyte glycoprotein (MOG), at EAE onset, or at peak disease severity. DNP treatments attenuated infiltration of effector T cells into the CNS and suppressed innate and adaptive immune responses to myelin oligodendrocyte glycoprotein immunization in spleen. Therapeutic responses were not observed in mice treated with cargo DNA or cationic polymers alone, indicating that DNP uptake and cargo DNA sensing by cells with regulatory functions was essential for therapeutic responses to manifest. Intact STING and IFN-αβ receptor genes, but not IFN-γ receptor genes, were essential for therapeutic responses to DNPs to manifest. Treatments with cyclic diguanylate monophosphate to activate STING also delayed EAE onset and reduced disease severity. Therapeutic responses to DNPs were critically dependent on IDO enzyme activity in hematopoietic cells. Thus, DNPs and cyclic diguanylate monophosphate attenuate EAE by inducing dominant T cell regulatory responses via the STING/IFN-αβ/IDO pathway that suppress CNS-specific autoimmunity. These findings reveal dichotomous roles for the STING/IFN-αβ pathway in either stimulating or suppressing autoimmunity and identify STING-activating reagents as a novel class of immune modulatory drugs.

Induction and role of indoleamine 2,3 dioxygenase in mouse models of influenza a virus infection.

Influenza infection stimulates protective host immune responses but paradoxically enhances lung indoleamine 2,3 dioxygenase (IDO) activity, an enzyme that suppresses helper/effector T cells and activates Foxp3-lineage regulatory CD4 T cells (Tregs). Influenza A/PR/8/34 (PR8) infection stimulated rapid elevation of IDO activity in lungs and lung-draining mediastinal lymph nodes (msLNs). Mice lacking intact IDO1 genes (IDO1-KO mice) exhibited significantly lower morbidity after sub-lethal PR8 infection, and genetic or pharmacologic IDO ablation led to much faster recovery after virus clearance. More robust influenza-specific effector CD8 T cell responses manifested in lungs of PR8-infected IDO1-KO mice, though virus clearance rates were unaffected by IDO ablation. Similar outcomes manifested in mice infected with a less virulent influenza A strain (X31). IDO induction in X31-infected lungs was dependent on IFN type II (IFNγ) signaling and was restricted to non-hematopoietic cells, while redundant IFN type 1 or type II signaling induced IDO exclusively in hematopoietic cells from msLNs. Memory T cells generated in X31-primed IDO1-KO mice protected mice from subsequent challenge with lethal doses of PR8 (100×LD50). However recall T cell responses were less robust in lung interstitial tissues, and classic dominance of TCR Vβ8.3 chain usage amongst memory CD8+ T cells specific for influenza nucleoprotein (NP366) did not manifest in IDO1-KO mice. Thus, influenza induced IDO activity in lungs enhanced morbidity, slowed recovery, restrained effector T cell responses in lungs and shaped memory T cell repertoire generation, but did not attenuate virus clearance during primary influenza A infection.

Altered Tryptophan Metabolism as a Paradigm for Good and Bad Aspects of Immune Privilege in Chronic Inflammatory Diseases

The term “immune privilege” was coined to describe weak immunogenicity (hypo-immunity) that manifests in some transplant settings. We extended this concept to encompass hypo-immunity that manifests at local sites of inflammation relevant to clinical diseases. Here, we focus on emerging evidence that enhanced tryptophan catabolism is a key metabolic process that promotes and sustains induced immune privilege, and discuss the implications for exploiting this knowledge to improve treatments for hypo-immune and hyper-immune syndromes using strategies to manipulate tryptophan metabolism.

Virus Infections Incite Pain Hypersensitivity by Inducing Indoleamine 2,3 Dioxygenase.

Increased pain sensitivity is a comorbidity associated with many clinical diseases, though the underlying causes are poorly understood. Recently, chronic pain hypersensitivity in rodents treated to induce chronic inflammation in peripheral tissues was linked to enhanced tryptophan catabolism in brain mediated by indoleamine 2,3 dioxygenase (IDO). Here we show that acute influenza A virus (IAV) and chronic murine leukemia retrovirus (MuLV) infections, which stimulate robust IDO expression in lungs and lymphoid tissues, induced acute or chronic pain hypersensitivity, respectively. In contrast, virus-induced pain hypersensitivity did not manifest in mice lacking intact IDO1 genes. Spleen IDO activity increased markedly as MuLV infections progressed, while IDO1 expression was not elevated significantly in brain or spinal cord (CNS) tissues. Moreover, kynurenine (Kyn), a tryptophan catabolite made by cells expressing IDO, incited pain hypersensitivity in uninfected IDO1-deficient mice and Kyn potentiated pain hypersensitivity due to MuLV infection. MuLV infection stimulated selective IDO expression by a discreet population of spleen cells expressing both B cell (CD19) and dendritic cell (CD11c) markers (CD19+ DCs). CD19+ DCs were more susceptible to MuLV infection than B cells or conventional (CD19neg) DCs, proliferated faster than B cells from early stages of MuLV infection and exhibited mature antigen presenting cell (APC) phenotypes, unlike conventional (CD19neg) DCs. Moreover, interactions with CD4 T cells were necessary to sustain functional IDO expression by CD19+ DCs in vitro and in vivo. Splenocytes from MuLV-infected IDO1-sufficient mice induced pain hypersensitivity in uninfected IDO1-deficient recipient mice, while selective in vivo depletion of DCs alleviated pain hypersensitivity in MuLV-infected IDO1-sufficient mice and led to rapid reduction in splenomegaly, a hallmark of MuLV immune pathogenesis. These findings reveal critical roles for CD19+ DCs expressing IDO in host responses to MuLV infection that enhance pain hypersensitivity and cause immune pathology. Collectively, our findings support the hypothesis elevated IDO activity in non-CNS due to virus infections causes pain hypersensitivity mediated by Kyn. Previously unappreciated links between host immune responses to virus infections and pain sensitivity suggest that IDO inhibitors may alleviate heightened pain sensitivity during infections.

Cutting edge: DNA sensing via the STING adaptor in myeloid dendritic cells s tolerogenic responses

Cytosolic DNA sensing via the stimulator of IFN genes (STING) adaptor incites autoimmunity by inducing type I IFN (IFN-αβ). In this study, we show that DNA is also sensed via STING to suppress immunity by inducing IDO. STING gene ablation abolished IFN-αβ and IDO induction by dendritic cells (DCs) after DNA nanoparticle (DNP) treatment. Marginal zone macrophages, some DCs, and myeloid cells ingested DNPs, but CD11b+ DCs were the only cells to express IFN-β, whereas CD11b+ non-DCs were major IL-1β producers. STING ablation also abolished DNP-induced regulatory responses by DCs and regulatory T cells, and hallmark regulatory responses to apoptotic cells were also abrogated. Moreover, systemic cyclic diguanylate monophosphate treatment to activate STING induced selective IFN-β expression by CD11b+ DCs and suppressed Th1 responses to immunization. Thus, previously unrecognized functional diversity among physiologic innate immune cells regarding DNA sensing via STING is pivotal in driving immune responses to DNA.

DNA sensing via the Stimulator of Interferon Genes (STING) adaptor in myeloid dendritic cells induces potent tolerogenic responses

Cytosolic DNA sensing via the stimulator of IFN genes (STING) adaptor incites autoimmunity by inducing type I IFN (IFN-αβ). In this study, we show that DNA is also sensed via STING to suppress immunity by inducing IDO. STING gene ablation abolished IFN-αβ and IDO induction by dendritic cells (DCs) after DNA nanoparticle (DNP) treatment. Marginal zone macrophages, some DCs, and myeloid cells ingested DNPs, but CD11b+ DCs were the only cells to express IFN-β, whereas CD11b+ non-DCs were major IL-1β producers. STING ablation also abolished DNP-induced regulatory responses by DCs and regulatory T cells, and hallmark regulatory responses to apoptotic cells were also abrogated. Moreover, systemic cyclic diguanylate monophosphate treatment to activate STING induced selective IFN-β expression by CD11b+ DCs and suppressed Th1 responses to immunization. Thus, previously unrecognized functional diversity among physiologic innate immune cells regarding DNA sensing via STING is pivotal in driving immune responses to DNA.