Contribution of interferon-beta to the immune activation induced by double-stranded DNA

Endothelial Activation in Orientia tsutsugamushi Infection Is Mediated by Cytokine Secretion From Infected Monocytes

Scrub typhus, caused by Orientia tsutsugamushi, is a common systemic infection in Asia. Delay in diagnosis and treatment can lead to vasculitis in the visceral organs and other complications. The mechanisms that drive endothelial activation and the inflammatory response in O. tsutsugamushi infection remain unknown. In addition, the interaction between monocytes and endothelial cells is still unclear. Here we demonstrate that O. tsutsugamushi-infected human dermal microvascular endothelial cells produced moderate levels of chemokines and low levels of IL-6 and IFN-β, but not TNF or IL-1β. Recombinant TNF and cytokine-rich supernatants from infected monocytes markedly enhanced chemokine production in infected endothelial cells. We also show that TNF and monocyte supernatants, but not O. tsutsugamushi infection of endothelial cells per se, upregulated the endothelial cell surface expression of ICAM-1, E-selectin, and tissue factor. This finding was consistent with the inability of O. tsutsugamushi to induce cytokine secretion from endothelial cells. The upregulation of surface molecules after stimulation with monocyte supernatants was significantly reduced by neutralizing anti-TNF antibodies. These results suggest that endothelial cell activation and response are mainly mediated by inflammatory cytokines secreted from monocytes.

Embryonic Neocortical Microglia Express Toll-Like Receptor 9 and Respond to Plasmid DNA Injected into the Ventricle: Technical Considerations Regarding Microglial Distribution in Electroporated Brain Walls

Microglia, the resident immune cells in the CNS, play multiple roles during development. In the embryonic cerebral wall, microglia modulate the functions of neural stem/progenitor cells through their distribution in regions undergoing cell proliferation and/or differentiation. Previous studies using CX3CR1-GFP transgenic mice demonstrated that microglia extensively survey these regions. To simultaneously visualize microglia and neural-lineage cells that interact with each other, we applied the in utero electroporation (IUE) technique, which has been widely used for gene-transfer in neurodevelopmental studies, to CX3CR1-GFP mice (males and females). However, we unexpectedly faced a technical problem: although microglia are normally distributed homogeneously throughout the mid-embryonic cortical wall with only limited luminal entry, the intraventricular presence of exogenously derived plasmid DNAs induced microglia to accumulate along the apical surface of the cortex and aggregate in the choroid plexus. This effect was independent of capillary needle puncture of the brain wall or application of electrical pulses. The microglial response occurred at plasmid DNA concentrations lower than those routinely used for IUE, and was mediated by activation of Toll-like receptor 9 (TLR9), an innate immune sensor that recognizes unmethylated cytosine-phosphate guanosine motifs abundant in microbial DNA. Administration of plasmid DNA together with oligonucleotide 2088, the antagonist of TLR9, partially restored the dispersed intramural localization of microglia and significantly decreased luminal accumulation of these cells. Thus, via TLR9, intraventricular plasmid DNA administration causes aberrant distribution of embryonic microglia, suggesting that the behavior of microglia in brain primordia subjected to IUE should be carefully interpreted.

Comparative analysis of pathologic processes developing in mice housed in SPF vs non-SPF conditions and treated with cyclophosphamide and dsDNA preparation

In our earlier studies, we observed that when mice are treated with cyclophosphamide and fragmented exogenous dsDNA (18-30 h post cytostatic treatment), they develop a very characteristic set of symptoms and 80-90% of such animals succumb within 6-25 days. This was called "delayed death" phenomenon, and the gap between cyclophosphamide and DNA injections required for such phenotype to develop was termed "death window". We established that mice succumbed to multi-organ failure, which was caused by systemic inflammation and sepsis. These processes unfolded along with accidental involution of lymphoid organs, which resulted from the failure of CD34(+) hematopoietic stem cells to differentiate into lymphoid lineage progenitors. Here we compare SPF and non-SPF animals, and demonstrate that the major cause of systemic inflammation and sepsis observed upon such treatments is activation of an opportunistic infection. Mice of the same strain (CBA) housed under SPF conditions do not develop the characteristic symptoms, nor do they become moribund. Yet, regardless of the breeding conditions, upon synergistic action of cyclophosphamide and dsDNA, CD34(+) hematopoietic stem cells consistently fail to give rise to lymphoid lineage progenitors. We demonstrate that this differentiation defect is reversible and that population of lymphoid progenitors is restored by day 29 after cyclophosphamide injection.

DNA-damage-induced type I interferon promotes senescence and inhibits stem cell function

Expression of type I interferons (IFNs) can be induced by DNA-damaging agents, but the mechanisms and significance of this regulation are not completely understood. We found that the transcription factor IRF3, activated in an ATM-IKKα/β-dependent manner, stimulates cell-autonomous IFN-β expression in response to double-stranded DNA breaks. Cells and tissues with accumulating DNA damage produce endogenous IFN-β and stimulate IFN signaling in vitro and in vivo. In turn, IFN acts to amplify DNA-damage responses, activate the p53 pathway, promote senescence, and inhibit stem cell function in response to telomere shortening. Inactivation of the IFN pathway abrogates the development of diverse progeric phenotypes and extends the lifespan of Terc knockout mice. These data identify DNA-damage-response-induced IFN signaling as a critical mechanism that links accumulating DNA damage with senescence and premature aging.

Harnessing DNA-induced immune responses for improving cancer vaccines

DNA vaccines have emerged as an attractive strategy to promote protective cellular and humoral immunity against the encoded antigen. DNA vaccines are easy to generate, inexpensive to produce and purify at large-scale, highly stable and safe. In addition, plasmids used for DNA vaccines act as powerful "danger signals" by stimulating several DNA-sensing innate immune receptors that promote the induction of protective adaptive immunity. The induction of tumor-specific immune responses represents a major challenge for DNA vaccines because most of tumor-associated antigens are normal non-mutated self-antigens. As a consequence, induction of potentially self-reactive T cell responses against such poorly immunogenic antigens is controlled by mechanisms of central and peripheral tolerance as well as tumor-induced immunosuppression. Although several DNA vaccines against cancer have reached clinical testing, disappointing results have been observed. Therefore, the development of new adjuvants that strongly stimulate the induction of antitumor T cell immunity and counteract immune-suppressive regulation is an attractive approach to enhance the potency of DNA vaccines and overcome tumor-associated tolerance. Understanding the DNA-sensing signaling pathways of innate immunity that mediate the induction of T cell responses elicited by DNA vaccines represents a unique opportunity to develop novel adjuvants that enhance vaccine potency. The advance of DNA adjuvants needs to be complemented with the development of potent delivery systems, in order to step toward successful clinical application. Here, we briefly discuss recent evidence showing how to harness DNA-induced immune response to improve the potency of cancer vaccines and counteract tumor-associated tolerance.

Induction of type I IFNs by intracellular DNA-sensing pathways

A successful antimicrobial immune response involves the coordinate action of cells and soluble factors, with the cytokine family of type I interferons (IFNs) having a central role. Type I IFNs are not only crucial in conferring immediate antimicrobial, most importantly antiviral effects, but they also have an essential role in bridging the innate with the adaptive immune response. Therefore, production of these key cytokines must be tightly controlled. To this effect the host has evolved a set of pattern recognition receptors (PRRs) that reliably and specifically detect the presence of microbial pathogens before mounting an IFN response. Most PRR pathways that are known to induce type I IFNs are triggered upon recognition of nucleic acids. This mode of sensing is not straightforward, as large amounts of RNA and DNA are also present within the host. Nevertheless, in some cases distinct molecular features that are present within foreign nucleic acids but absent in endogenous nucleic acids, allow the host to reliably discriminate between 'self' and 'non-self'. At the same time, compartmentalization of PRRs within subcellular organelles that are usually devoid of host nucleic acids, but are sites of pathogen localization, is another principle that enables the host to distinguish self from non-self. The latter mode of sensing applies to the detection of microbial DNA within the cytoplasm, a compartment in which host DNAs are usually not present. Despite the past years' tremendous progress in the field of innate immunity, our understanding of cytoplasmic DNA sensing mechanisms is only beginning to form/take form. In this review, we outline the recent advancements in the elucidation of intracellular DNA-sensing pathways and discuss the future directions of this emerging field.

Cytosolic DNA-activated human dendritic cells are potent activators of the adaptive immune response

Recent studies in cell lines and genetically engineered mice have demonstrated that cytosolic dsDNA could activate dendritic cells (DCs) to become effector APCs. Recognition of DNA might be a major factor in antimicrobial immune responses against cytosolic pathogens and also in human autoimmune diseases such as systemic lupus erythematosus. However, the role of cytosolic dsDNA in human DC activation and its effects on effector T and B cells are still elusive. In this study, we demonstrate that intracellular dsDNA is a potent activator of human monocyte-derived DCs as well as primary DCs. Activation by dsDNA depends on NF-κB activation, partially on the adaptor molecule IFN-promoter stimulator-1 and the novel cytosolic dsDNA receptor IFI16, but not on the previously recognized dsDNA sentinels absent in melanoma 2, DNA-dependent activator of IFN regulatory factor 3, RNA polymerase III, or high-mobility group boxes. More importantly, we report for the first time, to our knowledge, that human dsDNA-activated DCs, rather than LPS- or inflammatory cytokine mixture-activated DCs, represent the most potent inducers of naive CD4(+) T cells to promote Th1-type cytokine production and generate CD4(+) and CD8(+) cytotoxic T cells. dsDNA-DCs, but not LPS- or mixture-activated DCs, induce B cells to produce complement-fixing IgG1 and IgG3 Abs. We propose that cytosolic dsDNA represents a novel, more effective approach to generate DCs to enhance vaccine effectiveness in reprogramming the adaptive immune system to eradicate infectious agents, autoimmunity, allergy, and cancer.

Evaluation of signal transduction pathways after transient cutaneous adenoviral gene delivery

Background

Adenoviral vectors have provided effective methods for in vivo gene delivery in therapeutic applications. However, these vectors can induce immune responses that may severely affect the ability of vector re-application. There is limited information about the mechanisms and signal transduction pathways involved in adenoviral recognition. For optimization of cutaneous gene therapy it is necessary to investigate molecular mechanisms of virus recognition in epidermal cells. The aim of this study was to investigate the signal transduction of the innate immunity after adenoviral DNA internalization in keratinocytes.

Methods

In vitro, keratinocytes were transfected with DNA, in the presence and absence of inhibitors for signalling molecules. In vivo, immunocompetent and athymic mice (n = 3 per group) were twice transduced with an Ad-vector.

Results

The results show an acute induction of type-I-interferon after in vitro transfection. Inhibition of PI3K, p38 MAPK, JNK and NFkappaB resulted in a decreased expression of type-I-interferon. In contrast to immunocompetent mice, athymic mice demonstrated a constant transgene expression and reduced inflammatory response in vivo.

Conclusion

The results suggest an induction of the innate immunity triggered by cytoplasm localised DNA which is mediated by PI3K-, p38 MAPK-, JNK-, NFkappaB-, JAK/STAT- and ERK1/2-dependent pathways. A stable transgene expression and a reduced inflammatory response in immunodeficient mice have been observed. These results provide potential for an effective adenoviral gene delivery into immunosupressed skin.

A strategy of tumor treatment in mice with doxorubicin-cyclophosphamide combination based on dendritic cell activation by human double-stranded DNA preparation

BACKGROUND

Immunization of mice with tumor homogenate after combined treatment with cyclophosphamide (CP) and double-stranded DNA (dsDNA) preparation is effective at inhibition of growth of tumor challenged after the treatment. It was assumed that this inhibition might be due to activation of the antigen-presenting cells. The purpose was to develop improved antitumor strategy using mice. We studied the combined action of cytostatics doxorubicin (Dox) plus CP with subsequent dsDNA preparation on tumor growth.

METHODS

Three-month old CBA/Lac mice were used in the experiments. Mice were injected with CP and human dsDNA preparation. The percentage of mature dendritic cells (DCs) was estimated by staining of mononuclear cells isolated from spleen and bone marrow 3, 6, and 9 days later with monoclonal antibodies CD34, CD80, and CD86. In the next set of experiments, mice were given intramuscularly injections of 1-3 × 105 tumor cells. Four days later, they were injected intravenously with 6-6.7 mg/kg Dox and intraperitoneally with 100-200 mg/kg CP; 200 mkg human DNA was injected intraperitoneally after CP administration. Differences in tumor size between groups were analyzed for statistical significance by Student's t-test. The MTT-test was done to determine the cytotoxic index of mouse leucocytes from treated groups.

RESULTS

The conducted experiments showed that combined treatment with CP and dsDNA preparation produce an increase in the total amount of mature DCs in vivo. Treatment of tumor bearers with preparation of fragmented dsDNA on the background of pretreatment with Dox plus CP demonstrated a strong suppression of tumor growth in two models. RLS, a weakly immunogenic, resistant to alkalyting cytostatics tumor, grew 3.4-fold slower when compared with the control (p < 0.001). In experiment with Krebs-2 tumor, only 2 of the 10 mice in the Dox+CP+DNA group had a palpable tumor on day 16. The cytotoxic index of leucocytes was 86.5% in the Dox+CP+DNA group, but it was 0% in the Dox+CP group.

CONCLUSIONS

Thus, the set of experiments we performed showed that exogenous dsDNA, when administered on the background of pretreatment with Dox plus CP, has an antitumor effect possibly due to DC activation.

Effect of double-stranded DNA on maturation of dendritic cells in vitro

A preparation of human genomic fragmented double-stranded DNA (dsDNA) was used as maturation stimulus in cultures of human dendritic cells (DCs) generated in compliance with the interferon protocol. Culturing of the DCs in medium with 5μg/ml of the DNA preparation was associated with a decrease in the relative proportion of CD14 + cells and an increase in that of CD83 + cells. These changes are markers of DC maturation. The efficiency with which the DNA preparation was able to elicit DC maturation was commensurate with that of lypopolysaccharide from bacterial cell, the standard inducer of DC maturation. Generated ex vivo, matured in the presence of the human DNA preparation, pulsed with tumor antigens mouse DCs were used as a vaccine in biological tests for its antitumor activity. The experimental results demonstrate that reinfusion of mature pulsed with tumor antigens DCs cause a statistically significant suppression of tumor graft growth.

Comparison of the type of liposome involving cytokine production induced by non-CpG Lipoplex in macrophages

To improve the transfection efficiency of plasmid DNA (pDNA) into cells, various types of cationic liposome have been used to prepare pDNA/cationic liposome complexes (lipoplexes). It is well-known that lipoplexes induce a large amount of proinflammatory cytokines because unmethylated CpG dinucleotides (CpG motifs) abundantly present in pDNA are recognized by Toll-like receptor-9 (TLR9) expressed in immune cells such as macrophages and dendritic cells. This nonspecific cytokine production is problematic in nonviral gene therapy. Moreover, recent studies have demonstrated that lipoplexes induce not only proinflammatory cytokines but also another type of cytokine, type I interferons (IFNs), irrespective of the frequency of CpG motifs in DNA and the expression of TLR9. To gain more insight into the CpG motif- and TLR9-independent induction of type I IFNs and proinflammatory cytokines by lipoplex, macrophage activation was evaluated in vitro using various cationic liposomes complexed with pDNA containing no CpG motifs. The production of IFN-beta, TNF-alpha and IL-6 by lipoplex was confirmed to be induced independently of the interaction between CpG DNA and TLR9 in macrophages from TLR9-knockout mice. Then, the release of the cytokines, the mRNA expression of Z-DNA binding protein-1 (Zbp1), a cytosolic double-stranded DNA sensor, and the cellular uptake of pDNA were examined in a macrophage-like cell line, RAW264.7. The level of cytokine production and the increase in the Zbp1 mRNA varied depending on the type of cationic liposome used. A good correlation was observed between the cytokine level and the Zbp1 mRNA. A confocal microscopic study using fluorescently labeled pDNA complexes showed that the complexes that released a lot of cytokines showed an enhanced distribution of pDNA-derived fluorescence into the cytosol. These results suggest that different intracellular trafficking derived from the type of liposomes determines the recognition of pDNA by ZBP1 after uptake of lipoplexes by the macrophages, followed by the release of type I IFNs and inflammatory cytokines. The present study demonstrates that cationic liposomes should be selected based on these findings for optimization of DNA-based therapies using lipoplexes.

Contribution of IRF-3 mediated IFNbeta production to DNA vaccine dependent cellular immune responses

The mechanism(s) by which DNA vaccines activate Ag-specific cellular immune responses is incompletely understood. Current findings indicate that IRF-3 plays an important role in this process. The IRF-3 dependent signaling pathway is triggered by the presence of intracytoplasmic DNA, and culminates in the production of type I IFNs. DNA vaccination of IRF-3 KO mice elicits a strong Ag-specific humoral response, yet CD4 and CD8 T cell responses (including the production of Th1, Th2 and Th 17 cytokines) are severely impaired. Although expression of the immunogenic protein encoded by the DNA vaccine was similar in IRF-3 KO vs wild type mice, antigen presentation was severely impaired in the KO animals. This defect was remedied by the co-delivery of an IFNbeta encoding plasmid. These findings suggest that the IRF-3/IFNbeta pathways are key to the induction of cellular immunity following DNA vaccination.

Cellular activation by plasmid DNA in various macrophages in primary culture

Macrophages are an important group of cells responsible for the inflammatory response to unmethylated CpG dinucleotide (CpG motif) in plasmid DNA (pDNA) via Toll-like receptor 9 (TLR9). This finding is primarily based on in vitro studies. Previous in vivo studies also have suggested that tissue macrophages are involved in inflammatory cytokine release in the circulation following intravenous administration of pDNA to mice. However, the relationship between the in vitro and in vivo studies has not been sufficiently clarified. To gain insight into which types of cells are responsible for the production of cytokines upon interaction with pDNA, peritoneal macrophages, splenic macrophages, hepatic nonparenchymal cells (NPCs) including Kupffer cells and mesangial cells were isolated from mice. All types of primary cultured cells, except for mesangial cells, express TLR9 at varying levels. Splenic macrophages and hepatic NPCs were activated to produce tumor necrosis factor-alpha (TNF-alpha) by naked pDNA, whereas peritoneal macrophages and mesangial cells were not. pDNA complexed with N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethyl-ammonium chloride/cholesterol liposome induced TNF-alpha in the splenic macrophages but not in the other cell types. These results indicate that splenic macrophages and hepatic NPCs are closely involved in TNF-alpha production in response to pDNA.

Toll-like receptor 3 activation induces antiviral immune responses in mouse sertoli cells

Toll-like receptors (TLRs) recognize pathogen-associated molecular patterns and elicit antimicrobial immune responses. In the testis, viruses can induce pathological conditions, such as orchitis, and may participate in the etiology of testicular cancer; however, the molecular mechanisms involved remain under investigation. It has been suggested that because they constitutively express interferon (IFN)-inducible antiviral proteins, Sertoli cells participate in the testicular antiviral defense system. Previously, we demonstrated a key function of mouse Sertoli cells in the bactericidal testicular defense mechanism mediated by a panel of TLRs. To better characterize the potential role of Sertoli cells in the response against testicular viral infections, we investigated the TLR3 expression and function in these cells. Sertoli cells express TLR3, and under stimulation with the synthetic double-stranded RNA analogue poly (I:C), they produce the proinflammatory molecule ICAM1 and secrete functionally active CCL2 chemokine. Using both pharmacological and genetic approaches, we found that these effects are TLR3-dependent. Moreover, using ELISA, we found that IFNA is constitutively produced and not further inducible, whereas IFNB1 is absent and dramatically induced only by transfected poly (I:C), indicating different control mechanisms underlying IFNA and IFNB1 production. To conclude, poly (I:C) elicits both inflammatory and antiviral responses in Sertoli cells.

The induction of HMGB1 release from RAW 264.7 cells by transfected DNA

High mobility group protein 1 (HMGB1) is a non-histone nuclear protein that can activate innate immunity when in an extracellular location. As shown in in vitro studies, while polyinosinic-polycytidylic acid [poly (I:C)] and LPS, TLR3 and TLR4 ligands, respectively, can induce HMGB1 release from macrophages, CpG DNA, a TLR 9 ligand, does not. Since DNA displays distinct immunostimulatory activity when transfected into cells, we investigated whether transfected DNA can induce HMGB1 release from macrophages. In these experiments, using RAW 264.7 cells as model, we show that DNA, either natural DNA or synthetic oligonucleotides, can induce HMGB1 release when used to stimulate cells with the transfection reagent Lipofectamine 2000; release occurred irrespective of the intrinsic activity of the DNA. The induction of HMGB1 release by transfected DNA was dependent on IFN-beta as shown by the inhibitory effects of an antibody. In addition, JNK activation mediated HMGB1 release induced by a transfected phosphorothioate oligonucleotide but not by transfected natural DNA. Together, these findings indicate that transfected DNA can stimulate macrophages to release HMGB1 under conditions in which free DNA is inactive and suggest a role of DNA in inducing inflammation when bound to molecules that influence its entry into cells.

Augmentation of effects of interferon-stimulated genes by reversal of epigenetic silencing: potential application to melanoma

Increased expression of genes, silenced by methylation of their promoters, could have relevance for increasing effects of not only interferons (IFNs) but also APO2L/TRAIL, cytotoxics and immunotherapeutics for melanoma and other malignancies. A resistant melanoma cell line, A375, lacked APO2L/TRAIL or apoptosis induction by either IFN-alpha2 or IFN-beta. However, apoptosis was induced by IFNs in A375 cells by 5-aza,2'-deoxycytidine (5-Aza-dC), evaluated based upon the postulate that promoter methylation might be silencing pro-apopoptotic IFN-stimulated genes (ISGs). RASSF1A, commonly methylated at high frequency in many tumors including melanoma, which we discovered to be also an IFN-regulated gene, was increased by 5-Aza-dC. RASSF1A was important in enhancing apoptotic effects of not only IFNs and APO2L/TRAIL but also cisplatin. Unraveling epigenetic regulatory mechanisms, as yet only partially identified, will result in new biological insights and improved strategies for therapeutic use of IFNs or ISGs such as APO2L/TRAIL.

Potential of Transfected Muscle Cells to Contribute to DNA Vaccine Immunogenicity

The mechanism(s) by which DNA vaccines trigger the activation of Ag-specific T cells is incompletely understood. A series of in vivo and in vitro experiments indicates plasmid transfection stimulates muscle cells to up-regulate expression of MHC class I and costimulatory molecules and to produce multiple cytokines and chemokines. Transfected muscle cells gain the ability to directly present Ag to CD8 T cells through an IFN-regulatory factor 3-dependent process. These findings suggest that transfected muscle cells at the site of DNA vaccination may contribute to the magnitude and/or duration of the immune response initiated by professional APCs.

Syndromes and complications of interferon therapy

PURPOSE OF REVIEW

Interferons are used to treat a variety of medical conditions. They are integral players in immunity and a number of immune-mediated complications can arise during interferon therapy. We have reviewed the occurrence of these complications, and the mechanisms behind them.

RECENT FINDINGS

Case reports and follow-up studies of large cohorts of patients on interferon therapy have confirmed that immune-mediated complications are uncommon but can occur in a number of different organ systems. IFNalpha production is induced by specific autoantibody-nuclear antigen immune complexes, and has a key role in the development and maintenance of autoimmunity in systemic lupus erythematosus.

SUMMARY

Interferon therapy can precipitate immune-mediated abnormalities de novo or can exacerbate an existing autoimmune tendency. This is manifest in the rise in titre of existing antibodies and in the development of clinical disease in patients with preexisting antibodies. Type I interferons have a key role in the development of systemic lupus erythematosus.