Epstein-Barr virus BRLF1 inhibits transcription of IRF3 and IRF7 and suppresses induction of interferon-β

Activation of interferon regulatory factors (IRFs) 3 and 7 is essential for the induction of Type I interferons (IFN) and innate antiviral responses, and herpesviruses have evolved mechanisms to evade such responses. We previously reported that Epstein-Barr virus BZLF1, an immediate-early (IE) protein, inhibits the function of IRF7, but the role of BRLF1, the other IE transactivator, in IRF regulation has not been examined. We now show that BRLF1 expression decreased induction of IFN-β, and reduced expression of IRF3 and IRF7; effects were dependent on N- and C-terminal regions of BRLF1 and its nuclear localization signal. Endogenous IRF3 and IRF7 RNA and protein levels were also decreased during cytolytic EBV infection. Finally, production of IFN-β was decreased during lytic EBV infection and was associated with increased susceptibility to superinfection with Sendai virus. These data suggest a new role for BRLF1 with the ability to evade host innate immune responses.     

Suppression of innate antiviral response by severe acute respiratory syndrome coronavirus M protein is mediated through the first transmembrane domain

Coronaviruses have developed various measures to evade innate immunity, We have previously shown that severe acute respiratory syndrome （SARS） coronavirus M protein suppresses type I interferon （IFN） production by impeding the formation of functional TRAF3-containing complex. In this study, we demonstrate that the IFN-antagonizing activity is specific to SARS coronavirus M protein and is mediated through its first transmembrane domain （TM 1） located at the N terminus. M protein from human coronavirus HKU 1 does not inhibit IFN production. Whereas N-linked glycosylation of SARS coronavirus M protein has no influence on IFN antagonism, TM1 is indispensable for the suppression of IFN production. TM 1 targets SARS coronavirus M protein and heterologous proteins to the Golgi apparatus, yet Golgi localization is required but not sufficient for IFN antagonism. Mechanistically, TM 1 is capable of binding with RIG-I, TRAF3, TBK1 and IKK~, and preventing the interaction of TRAF3 with its downstream effectors. Our work defines the molecular architecture of SARS coronavirus M orotein reouired for suooression of innate antiviral re~nnn~e.     

IRF3 and IRF7 contribute to diesel exhaust particles-induced pulmonary inflammation by mediating mTORC1 activation and restraining autophagy in mice

Exposure to diesel exhaust particles (DEPs) is associated with acute inflammatory responses in the lung and exacerbation of respiratory diseases. However, the mechanism by which DEPs trigger the inflammatory responses remains unclear. Here, we demonstrated that the IFN response factors IRF3 and IRF7 played pivotal roles in DEP-induced pulmonary inflammation. DEPs could not directly induce inflammatory cytokine expression in mouse cells, whereas DEPs triggered autophagy both in vitro and in vivo. The DEP-induced autophagy was augmented in the absence of IRF3 and IRF7, but not in the absence of IFNAR. The expression of Raptor was induced by IRF3 and IRF7 in response to DEPs treatment. Furthermore, administration of the mechanistic target of rapamycin (mTOR) inhibitor alleviated the inflammatory responses in the lung during DEP exposure. Our findings define an IFNAR-independent role of increased autophagy in the absence of IRF3 and IRF7 during pulmonary DEP exposure, and provide the basis to develop new therapeutic approaches to counteract the adverse effects of DEPs and possibly other ambient particulate matters.     

Targeting 7-Dehydrocholesterol Reductase Integrates Cholesterol Metabolism and IRF3 Activation to Eliminate Infection

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TLR3 and TLR4 are innate antiviral immune receptors in human microglia: Role of IRF3 in modulating antiviral and inflammatory response in the CNS

In the CNS, microglia are the primary targets of HIV infection. In this study, we investigated the effect of activation of the innate antiviral receptors TLR3 and TLR4 on HIV infection of primary human microglia, as well as microglial cell signaling and gene expression. Ligands for both TLR3 and TLR4 potently inhibited HIV replication in microglia through a pathway requiring IRF3. Surprisingly, a remarkably similar pattern of cell signaling and gene expression was observed in TLR3- and TLR4-activated microglia, suggesting a relatively minor role for MyD88 following TLR4 activation in these cells. HIV did not activate IRF3 but rather decreased IRF3 protein, indicating that HIV does not activate TLR3 or RIG-like helicases in microglia. Taken together, these results indicate that activation of TLR3 or TLR4 will elicit antiviral immunity, in addition to inducing proinflammatory responses. We suggest that a balanced expression between inflammatory and innate immune genes might be achieved by IRF3 over-expression.     

VRK2 is involved in the innate antiviral response by promoting mitostress-induced mtDNA release

Mitochondrial stress (mitostress) triggered by viral infection or mitochondrial dysfunction causes the release of mitochondrial DNA (mtDNA) into the cytosol and activates the cGAS-mediated innate immune response. The regulation of mtDNA release upon mitostress remains uncharacterized. Here, we identified mitochondria-associated vaccinia virus-related kinase 2 (VRK2) as a key regulator of this process. VRK2 deficiency inhibited the induction of antiviral genes and caused earlier and higher mortality in mice after viral infection. Upon viral infection, VRK2 associated with voltage-dependent anion channel 1 (VDAC1) and promoted VDAC1 oligomerization and mtDNA release, leading to the cGAS-mediated innate immune response. VRK2 was also required for mtDNA release and cGAS-mediated innate immunity triggered by nonviral factors that cause Ca²⁺ overload but was not required for the cytosolic nucleic acid-triggered innate immune response. Thus, VRK2 plays a crucial role in the mtDNA-triggered innate immune response and may be a potential therapeutic target for infectious and autoimmune diseases associated with mtDNA release.     

Toll-like receptor 3 agonist poly(I:C)-induced antiviral response in human corneal epithelial cells

The objective of this study was to examine the expression of Toll-like receptor 3 (TLR3) by human corneal epithelial cells (HCECs) and to determine whether exposure to the TLR3 agonist polyinosinic-polycytidylic acid [poly(I:C)] induces an antiviral response in these cells. Fluorescence-activated cell sorter (FACS) analysis revealed TLR3 to be constitutively expressed and distributed intracellularly in HCECs. Stimulation of HCECs with the TLR3 agonist poly(I:C) induced the activation of nuclear factor (NF)-kappaB and production of the proinflammatory cytokine interleukin (IL)-6 and the chemokine IL-8. Upon exposure to poly(I:C), HCECs initiated a potent antiviral response resulting in an increase of interferon (IFN)-beta mRNA expression (7-fold). Poly(I:C) stimulation also up-regulated mRNA expression of the antiviral chemokine IFN-gamma inducible protein 10 (IP10), myxovirus resistance gene A and 2',5'-oligoadenylate synthetase (5-, 10- and 9-fold, respectively), and secretion of IP10. These responses were also induced by exogenously added type 1 IFNs, but could not be blocked by pretreatment of the cells with anti-TLR3 monoclonal antibody, suggesting that the receptor was not expressed on the cell surface. Furthermore, incubation of HCECs with an endosomal acidification inhibitor, chloroquine, markedly inhibited poly(I:C)-mediated IFN-beta expression in HCECs. These results suggest that corneal epithelial cells are important sentinels of the corneal innate immune system against viral infection, and that stimulation of TLR3 can induce the expression of key proinflammatory cytokines and chemokines and antiviral genes that help in the defence of the cornea against viral infection.     

TLR8 and TLR7 are involved in the host's immune response to human parechovirus 1

Toll-like receptors (TLR) have a key role in regulating immunity against microbial agents. Engagement of TLR by bacterial, viral or fungal components leads to the production and release of inflammatory cytokines. In this study we show that mainly TLR8 and also TLR7 act as the host sensors for human parechovirus 1, a single-stranded RNA (ssRNA) virus. Furthermore, we see that the viral ssRNA genome is detected in endosomal compartments by these TLR, which activate signalling that lead to the synthesis of pro-inflammatory molecules by the host.     

Immunology in the clinic review series; focus on type 1 diabetes and viruses: the innate immune response to enteroviruses and its possible role in regulating type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease arising as a consequence of a misdirected T cell response to the pancreatic beta cell. In recent years, there has been a growing interest in the innate immune system as a regulator of disease development. Genome-wide association studies have identified diabetes-associated polymorphisms in genes encoding proteins with functions related to the innate immune response. Moreover, enteroviruses, known to activate a strong innate immune response, have been implicated in the disease pathogenesis. In this review, we discuss the innate immune response elicited by enteroviruses and how this response may regulate T1D development.     

MicroRNA-33/33* inhibit the activation of MAVS through AMPK in antiviral innate immunity

Innate immunity plays a prominent role in the host defense against pathogens and must be precisely regulated. As vital orchestrators in cholesterol homeostasis, microRNA-33/33* have been widely investigated in cellular metabolism. However, their role in antiviral innate immunity is largely unknown. Here, we report that VSV stimulation decreased the expression of miR-33/33* through an IFNAR-dependent manner in macrophages. Overexpression of miR-33/33* resulted in impaired RIG-I signaling, enhancing viral load and lethality whereas attenuating type I interferon production both in vitro and in vivo. In addition, miR-33/33* specifically prevented the mitochondrial adaptor mitochondrial antiviral-signaling protein (MAVS) from forming activated aggregates by targeting adenosine monophosphate activated protein kinase (AMPK), subsequently impeding the mitophagy-mediated elimination of damaged mitochondria and disturbing mitochondrial homeostasis which is indispensable for efficient MAVS activation. Our findings establish miR-33/33* as negative modulators of the RNA virus-triggered innate immune response and identify a previously unknown regulatory mechanism linking mitochondrial homeostasis with antiviral signaling pathways.     

Listeria monocytogenes induces an interferon‐enhanced activation of the integrated stress response that is detrimental for resolution of infection in mice

Type I interferons (IFNs) induce a detrimental response during Listeria monocytogenes (L. monocytogenes) infection. We were interested in identifying mechanisms linking IFN signaling to negative host responses against L. monocytogenes infection. Herein, we found that infection of myeloid cells with L. monocytogenes led to a coordinated induction of type I IFNs and activation of the integrated stress response (ISR). Infected cells did not induce Xbp1 splicing or BiP upregulation, indicating that the unfolded protein response was not triggered. CHOP (Ddit3) gene expression was upregulated during the ISR activation induced by L. monocytogenes. Myeloid cells deficient in either type I IFN signaling or PKR activation had less upregulation of CHOP following infection. CHOP‐deficient mice showed lower expression of innate immune cytokines and were more resistant than wild‐type counterparts following L. monocytogenes infection. These findings indicate that L. monocytogenes infection induces type I IFNs, which activate the ISR through PKR, which contributes to a detrimental outcome in the infected host.     

The B7-H4 gene induces immune escape partly via upregulating the PD-1/Stat3 pathway in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is associated with high mortality rates worldwide. The costimulatory molecule, B7-H4, a member of the B7 family, plays an important role in immune regulation, mainly by inhibiting the proliferation of T cells to achieve a negative regulatory T cell immune response. The mechanism of action of B7-H4 in non-small cell lung cancer is unknown at present. Tumor tissues from 71 patients subjected to radical pneumonectomy were examined, along with NSCLC cells and BALB/c mice. Among the 71 NSCLC cases, overall and recurrence-free survival rates were significantly lower in those displaying high B7-H4 expression. Mechanistic analyses showed that B7-H4 promoted the growth and metastasis of non-small cell lung cancer tumor tissues in mice through effects on CD8⁺ T cell apoptosis. Data from western blot experiments further suggested that B7-H4 induced CD8⁺ T cell death, both in vitro and in vivo, and affecting the PD-1/Stat3 pathway and promoting immune escape of tumor cells. Our collective findings support the potential utility of B7-H4 gene expression as a marker of NSCLC prognosis and provide a novel strategy for targeted therapy.     

HCV-NS3重组腺病毒转染树突状细胞体内诱导抗原特异性Th1应答的研究

目的:探讨表达丙型肝炎病毒(HCV)非结构蛋白(NS3)基因的重组腺病毒转染树突状细胞体内诱导特异性Th1细胞免疫应答。方法:分离培养小鼠骨髓树突状细胞,制备表达HCV-NS3蛋白的重组腺病毒转染树突状细胞(DC-AdNS3)疫苗,采用流式细胞术和免疫印迹法分析鉴定细胞及抗原蛋白表达。采用腹腔注射途径免疫接种BALB/c小鼠两次,每次间隔10天,3×105细胞/次。末次接种10天后,采用ELISPOT法和ELISA法分别测定脾NS3特异性分泌IFN-γ的T细胞反应以及细胞因子水平。结果:重组腺病毒转染DC可刺激DC成熟,同时可在DC内成功表达NS3蛋白。小鼠两次接种DC-AdNS3产生明显升高的分泌IFN-γ的T细胞反应(P<0·01),脾T细胞悬液内可测得高水平的IL-2和IFN-γ(P<0·01)以及显著降低的IL-10(P<0·05)。结论:DC-AdNS3疫苗可在BALB/c小鼠体内激发产生抗原特异性的Th1细胞免疫应答,为抗HCV感染的疫苗研究提供参考依据。