In Vitro and In Vivo Evaluation of Virus-Induced Innate Immunity in Mouse.

The innate immune system is the first line of host defense against infection by pathogenic microorganisms, among which macrophages are important innate immune cells. Macrophages are widely distributed throughout the body and recognize and eliminate viruses through pattern recognition receptors (PRRs) to sense pathogen-associated molecular patterns (PAMPs). In the present chapter, we provide detailed protocols for vesicular stomatitis virus (VSV) amplification, VSV titer detection, isolation of mouse primary peritoneal macrophages, in vitro and in vivo VSV infection, detection of interferon-beta (IFN-ß) expression, and lung injury. These protocols provide efficient and typical methods to evaluate virus-induced innate immunity in vitro and in vivo.

RNF19a inhibits antiviral immune response to RNA viruses through degradation of TBK1.

TANK-binding kinase 1 (TBK1) plays a pivotal role in antiviral innate immunity. TBK1 mediates the activation of interferon regulatory factor (IRF) 3, leading to the induction of type I IFNs (IFN-α/ß) and of NF-κB signal transduction following viral infections. TBK1 must be tightly regulated to effectively control viral infections and maintain immune homeostasis. Here, we found that E3 ubiquitin ligase RNF19a mediated K48-linked ubiquitination and proteasomal degradation of TBK1. Specifically, the silence of RNF19a enhanced the production of type I interferons and suppressed RNA viral replication. Our results uncover that RNF19a acts as a negative mediator in the RIG-I signaling pathway to attenuate antiviral immune responses and suggest RNF19a as a potential therapy target in clinical infectious and inflammatory diseases.

IRF3-binding lncRNA-ISIR strengthens interferon production in viral infection and autoinflammation.

Interferon regulatory factor 3 (IRF3) is an essential transductor for initiation of many immune responses. Here, we show that lncRNA-ISIR directly binds IRF3 to promote its phosphorylation, dimerization, and nuclear translocation, along with enhanced target gene productions. In vivo lncRNA-ISIR deficiency results in reduced IFN production, uncontrolled viral replication, and increased mortality. The human homolog, AK131315, also binds IRF3 and promotes its activation. More important, AK131315 expression is positively correlated with type I interferon (IFN-I) level and severity in patients with lupus. Mechanistically, in resting cells, IRF3 is bound to suppressor protein Flightless-1 (Fli-1), which keeps its inactive state. Upon infection, IFN-I-induced lncRNA-ISIR binds IRF3 at DNA-binding domain in cytoplasm and removes Fli-1's association from IRF3, consequently facilitating IRF3 activation. Our results demonstrate that IFN-I-inducible lncRNA-ISIR feedback strengthens IRF3 activation by removing suppressive Fli-1 in immune responses, revealing a method of lncRNA-mediated modulation of transcription factor (TF) activation.

TLR5-Mediated Reactivation of Quiescent Ranavirus FV3 in Xenopus Peritoneal Macrophages.

Ranaviruses such as frog virus 3 (FV3) are large double-stranded DNA (dsDNA) viruses causing emerging infectious diseases leading to extensive morbidity and mortality of amphibians and other ectothermic vertebrates worldwide. Among the hosts of FV3, some are highly susceptible, whereas others are resistant and asymptomatic carriers that can take part in disseminating the infectious virus. To date, the mechanisms involved in the processes of FV3 viral persistence associated with subclinical infection transitioning to lethal outbreaks remain unknown. Investigation in Xenopus laevis has revealed that in asymptomatic FV3 carrier animals, inflammation induced by heat-killed (HK) Escherichia coli stimulation can provoke the relapse of active infection. Since Toll-like receptors (TLRs) are critical for recognizing microbial molecular patterns, we investigated their possible involvement in inflammation-induced FV3 reactivation. Among the 10 different TLRs screened for changes in expression levels following FV3 infection and HK E. coli stimulation, only TLR5 and TLR22, both of which recognize bacterial products, showed differential expression, and only the TLR5 ligand flagellin was able to induce FV3 reactivation similarly to HK E. coli Furthermore, only the TLR5 ligand flagellin induced FV3 reactivation in peritoneal macrophages both in vitro and in vivo These data indicate that the TLR5 signaling pathway can trigger FV3 reactivation and suggest a role of secondary bacterial infections or microbiome alterations (stress or pollution) in initiating sudden deadly disease outbreaks in amphibian populations with detectable persistent asymptomatic ranavirus.IMPORTANCE This study in the amphibian Xenopus laevis provides new evidence of the critical role of macrophages in the persistence of ranaviruses in a quiescent state as well as in the reactivation of these pathogens into a virulent infection. Among the multiple microbial sensors expressed by macrophages, our data underscore the preponderant involvement of TLR5 stimulation in triggering the reactivation of quiescent FV3 in resident peritoneal macrophages, unveiling a mechanistic connection between the reactivation of persisting ranavirus infection and bacterial coinfection. This suggests a role for secondary bacterial infections or microbiome alterations (stress or pollution) in initiating sudden deadly disease outbreaks in amphibian populations with detectable persistent asymptomatic ranavirus.

Scavenger receptor A1 participates in uptake of Leptospira interrogans serovar Autumnalis strain 56606v and inflammation in mouse macrophages.

Leptospirosis, caused by pathogenic Leptospira species, has emerged as a widespread zoonotic disease worldwide. Macrophages mediate the elimination of pathogens through phagocytosis and cytokine production. Scavenger receptor A1 (SR-A1), one of the critical receptors mediating this process, plays a complicated role in innate immunity. However, the role of SR-A1 in the immune response against pathogenic Leptospira invasion is unknown. In the present study, we found that SR-A1 is an important nonopsonic phagocytic receptor on murine macrophages for Leptospira. However, intraperitoneal injection of leptospires into WT mice presented with more apparent jaundice, subcutaneous hemorrhaging, and higher bacteria burdens in blood and tissues than that of SR-A1-/- mice. Exacerbated cytokine and inflammatory mediator levels were also observed in WT mice and higher recruited macrophages in the liver than those of SR-A1-/- mice. Our findings collectively reveal that although beneficial in the uptake of Leptospira by macrophage, SR-A1 might be exploited by Leptospira to modulate inflammatory activation and increase the susceptibility of infection in the host. These results provide our new insights into the innate immune response during early infection by L. interrogans.

Increased phagocytosis in the presence of enhanced M2-like macrophage responses correlates with increased primary and latent HSV-1 infection.

After HSV-1 infection, macrophages infiltrate early into the cornea, where they play an important role in HSV-1 infection. Macrophages are divided into M1 or M2 groups based on their activation. M1 macrophages are pro-inflammatory, while M2 macrophages are anti-inflammatory. Macrophage phenotypes can shift between M1 or M2 in vitro and in vivo following treatment with specific cytokines. In this study we looked at the effect of M2 macrophages on HSV-1 infectivity using mice either lacking M2 (M2-/-) or overexpressing M2 (M2-OE) macrophages. While presence or absence of M2 macrophages had no effect on eye disease, we found that over expression of M2 macrophages was associated with increased phagocytosis, increased primary virus replication, increased latency, and increased expression of pro- and anti-inflammatory cytokines. In contrast, in mice lacking M2 macrophages following infection phagocytosis, replication, latency, and cytokine expression were similar to wild type mice. Our results suggest that enhanced M2 responses lead to higher phagocytosis, which affected both primary and latent infection but not reactivation.

Matrine exhibits antiviral activity in a PRRSV/PCV2 co-infected mouse model.

BACKGROUND: PRRSV and PCV2 co-infection is very common in swine industry which results in huge economic losses worldwide. Although vaccination is used to prevent viral diseases, immunosuppression induced by PRRSV and PCV2 leads to vaccine failure. PURPOSE: Our previous results have demonstrated that Matrine possess antiviral activities against PRRSV/PCV2 co-infection in vitro. This study aims to establish a PRRSV/PCV2 co-infected KM mouse model and evaluate the antiviral activities of Matrine against PRRSV/PCV2 co-infection. STUDY DESIGN: A total of 144 KM mice were randomly divided into six groups with 24 mice in each group, named as: normal control, PRRSV/PCV2 co-infected group (PRRSV/PCV2 group), Ribavirin treatment positive control (Ribavirin control) and Matrine treatment groups (Matrine 40 mg/kg, Matrine 20 mg/kg and Matrine 10 mg/kg). METHODS: Except normal control group, all mice in other five groups were inoculated with PRRSV, followed by PCV2 at 2 h later. At 7 days post-infection (dpi), mice in the treatment groups were intraperitoneally administered with various doses of Matrine and Ribavirin, twice a day for 5 consecutive days. RESULTS: PRRSV N and PCV2 CAP genes were detected by PCR in multiple tissues including heart, liver, spleen, lungs, kidneys, thymus and inguinal lymph nodes. The viral load of PCV2 was the highest in liver followed by thymus and spleen. Although PRRSV were detected in most of tissues, but the replication of PRRSV was not significantly increased, as shown by qPCR analysis. Comparing with PCV2 infection alone, PRRSV infection significantly elevated PCV2 replication and exacerbated PCV2 induced interstitial pneumonia. qPCR analysis demonstrated 40 mg/kg Matrine significantly attenuated PCV2 replication in liver and alleviated virus induced interstitial pneumonia, suggesting Matrine could directly inhibit virus replication. In addition, Matrine treatment enhanced peritoneal macrophages phagocytosis at 13 and 16 dpi, and 40 mg/kg of Matrine increased the proliferation activity of lymphocytes. Body weight gain was continuously promoted by administrating Matrine at 10 mg/kg. CONCLUSION: Matrine possessed antiviral activities via inhibiting virus replication and regulating immune functions in mice co-infected by PRRSV/PCV2. These data provide new insight into controlling PRRSV and PCV2 infection and support further research for developing Matrine as a new possible veterinary medicine.

Macrophage HIV-1 Gene Expression and Delay Resolution of Inflammation in HIV-Tg Mice.

While antiretroviral therapy increases the longevity of people living with HIV (PLWH), about 30% of this population suffers from three or more concurrent comorbidities, whose mechanisms are not well understood. Chronic activation and dysfunction of the immune system could be one potential cause of these comorbidities. We recently demonstrated reduced macrophage infiltration and delayed resolution of inflammation in the lungs of HIV-transgenic mice. Additionally, trans-endothelial migration of HIV-positive macrophages was reduced in vitro. Here, we analyze macrophages' response to LPS challenge in the kidney and peritoneum of HIV-Tg mice. In contrast to the lung infiltration, renal and peritoneal macrophage infiltrations were similar in WT and HIV-Tg mice. Higher levels of HIV-1 gene expression were detected in lung macrophages compared to peritoneal macrophages. In peritoneal macrophages, HIV-1 gene expression was increased when they were cultured at 21% O2 compared to 5% O2, inversely correlating with reduced trans-endothelial migration at higher oxygen levels in vitro. The resolution of macrophage infiltration was reduced in both the lung and the peritoneal cavity of HIV-Tg mice. Taken together, our study described the organ-specific alteration of macrophage dynamics in HIV-Tg mice. The delayed resolution of macrophage infiltration might constitute a risk factor for the development of multiple comorbidities in PLWH.

Foot and mouth disease virus undergoes non-progressive replication in mice peritoneal macrophages and induces M1 polarization.

Despite the fact that macrophages link the innate and adaptive arms of immunity, it's role in the early infection of foot and mouth disease virus (FMDV) is largely unknown. Recently, depletion of macrophages in vivo after vaccination has shown to drastically diminish the protection against FMDV challenge in mouse model. Even the ability of macrophages to reduce or resist FMDV infection is not known hitherto. Therefore, we examined the replication ability of FMDV in mice peritoneal macrophages and the responsiveness in terms of macrophage polarization and cytokine production. Negative strand specific RT-PCR indicated replication of FMDV RNA in macrophages. Absolute quantitation of FMDV transcripts, immunofluorescence studies and titre of the infectious progeny virus revealed that replication peaked at 12 hpi and significantly declined by 18 hpi indicating non-progressive replication in the infected macrophages. Further, significant up regulation of inducible nitric oxide synthase by 8 -12 hpi and increase of M1 specific CD11c + cells by 42.6 % after infection showed that FMDV induce M1 polarization. A significant up regulation of TNFα and IL12 transcripts at 8 hpi supported that M1 macrophages were functional. Further, we studied the expression of Type I to III interferons (IFN) and other antiviral molecules. The results indicate a marked up regulation of Type I IFNα and ß by 9.2 and 11.2 fold, respectively at 8 hpi. Of the four IFN stimulated genes (ISG), viperin showed a significant up regulation by 286-fold at 12 hpi in the mice macrophages. In conclusion, the results suggest that replication of FMDV in mice peritoneal macrophages is non-progressive with up regulation of Type I IFN and ISGs. Further, FMDV induces M1 polarization in murine peritoneal macrophages.

Mitochondria-localised ZNFX1 functions as a dsRNA sensor to initiate antiviral responses through MAVS.

In the past two decades, emerging studies have suggested that DExD/H box helicases belonging to helicase superfamily 2 (SF2) play essential roles in antiviral innate immunity. However, the antiviral functions of helicase SF1, which shares a conserved helicase core with SF2, are little understood. Here we demonstrate that zinc finger NFX1-type containing 1 (ZNFX1), a helicase SF1, is an interferon (IFN)-stimulated, mitochondrial-localised dsRNA sensor that specifically restricts the replication of RNA viruses. Upon virus infection, ZNFX1 immediately recognizes viral RNA through its Armadillo-type fold and P-loop domain and then interacts with mitochondrial antiviral signalling protein to initiate the type I IFN response without depending on retinoic acid-inducible gene I-like receptors (RLRs). In short, as is the case with interferon-stimulated genes (ISGs) alone, ZNFX1 can induce IFN and ISG expression at an early stage of RNA virus infection to form a positively regulated loop of the well-known RLR signalling. This provides another layer of understanding of the complexity of antiviral immunity.

N 6-methyladenosine RNA modification-mediated cellular metabolism rewiring inhibits viral replication.

Host cell metabolism can be modulated by viral infection, affecting viral survival or clearance. Yet the cellular metabolism rewiring mediated by the N 6-methyladenosine (m6A) modification in interactions between virus and host remains largely unknown. Here we report that in response to viral infection, host cells impair the enzymatic activity of the RNA m6A demethylase ALKBH5. This behavior increases the m6A methylation on α-ketoglutarate dehydrogenase (OGDH) messenger RNA (mRNA) to reduce its mRNA stability and protein expression. Reduced OGDH decreases the production of the metabolite itaconate that is required for viral replication. With reduced OGDH and itaconate production in vivo, Alkbh5-deficient mice display innate immune response-independent resistance to viral exposure. Our findings reveal that m6A RNA modification-mediated down-regulation of the OGDH-itaconate pathway reprograms cellular metabolism to inhibit viral replication, proposing potential targets for controlling viral infection.

The long noncoding RNA Lnczc3h7a promotes a TRIM25-mediated RIG-I antiviral innate immune response.

The helicase RIG-I initiates an antiviral immune response after recognition of pathogenic RNA. TRIM25, an E3 ubiquitin ligase, mediates K63-linked ubiquitination of RIG-I, which is crucial for RIG-I downstream signaling and the antiviral innate immune response. The components and mode of the RIG-I-initiated innate signaling remain to be fully understood. Here we identify a novel long noncoding RNA (Lnczc3h7a) that binds to TRIM25 and promotes RIG-I-mediated antiviral innate immune responses. Depletion of Lnczc3h7a impairs RIG-I signaling and the antiviral innate response to RNA viruses in vitro and in vivo. Mechanistically, Lnczc3h7a binds to both TRIM25 and activated RIG-I, serving as a molecular scaffold for stabilization of the RIG-I-TRIM25 complex at the early stage of viral infection. Lnczc3h7a facilitates TRIM25-mediated K63-linked ubiquitination of RIG-I and thus promotes downstream signaling transduction. Our findings reveal that host RNAs can enhance the response of innate immune sensors to foreign RNAs, ensuring effective antiviral defense.

Boswellia serrata oleo-gum-resin and ß-boswellic acid inhibits HSV-1 infection in vitro through modulation of NF-кB and p38 MAP kinase signaling.

BACKGROUND: Herpes Simplex Virus (HSV), a highly contagious pathogen, is responsible for causing lifelong oral to genital infection in human. Boswellia serrata oleo-gum-resin possesses a strong traditional background of treating diverse skin ailments including infection but its effect on HSV-1 has not been examined yet. PURPOSE: To exploit its potential, we aimed to explore the antiviral activity of methanol extract of B. serrata oleo-gum-resin (BSE) and one of its major constituent ß-boswellic acid (BA) against HSV-1 along with the underlying mechanism of action involved. METHODS: BSE was subjected to RP-HPLC analysis to quantify the active constituent. Cytotoxicity (CC50) and antiviral activity were evaluated by MTT and plaque reduction assay, followed by the determination of median effective concentration (EC50). The mode of antiviral activity was assessed by time-of-addition assay and confirmed by reverse transcriptase-PCR (RT-PCR). Further, the expressions of various cytokines were measured by RT-PCR, while the proteins by Western blot. RESULTS: BSE and BA potently inhibited wild-type and a clinical isolate of HSV-1 (EC50 5.2-6.2 and 12.1-14.63 µg/ml), with nearly-complete inhibition (EC99) at 10 and 30 µg/ml, respectively. The inhibitory effect was significant at 1 h post-infection and effective up to 4 h. Based on target analysis we examined the inhibition of NF-κB, essential for virus replication, and observed significant down-regulation of NF-κB, and p38 MAP-kinase activation, with reduced expression of tumor necrosis factor (TNF)-α, Interleukin (IL)-1ß and IL-6, involved in scheming NF-κB signaling. CONCLUSION: Thus, our results support the ethnomedicinal use of BSE in skin infection by inhibiting HSV-1 through the modulation of NF-κB and p38 MAPK pathway.

EcoHIV infection of mice establishes latent viral reservoirs in T cells and active viral reservoirs in macrophages that are sufficient for induction of neurocognitive impairment.

Suppression of HIV replication by antiretroviral therapy (ART) or host immunity can prevent AIDS but not other HIV-associated conditions including neurocognitive impairment (HIV-NCI). Pathogenesis in HIV-suppressed individuals has been attributed to reservoirs of latent-inducible virus in resting CD4+ T cells. Macrophages are persistently infected with HIV but their role as HIV reservoirs in vivo has not been fully explored. Here we show that infection of conventional mice with chimeric HIV, EcoHIV, reproduces physiological conditions for development of disease in people on ART including immunocompetence, stable suppression of HIV replication, persistence of integrated, replication-competent HIV in T cells and macrophages, and manifestation of learning and memory deficits in behavioral tests, termed here murine HIV-NCI. EcoHIV established latent reservoirs in CD4+ T lymphocytes in chronically-infected mice but could be induced by epigenetic modulators ex vivo and in mice. In contrast, macrophages expressed EcoHIV constitutively in mice for up to 16 months; murine leukemia virus (MLV), the donor of gp80 envelope in EcoHIV, did not infect macrophages. Both EcoHIV and MLV were found in brain tissue of infected mice but only EcoHIV induced NCI. Murine HIV-NCI was prevented by antiretroviral prophylaxis but once established neither persistent EcoHIV infection in mice nor NCI could be reversed by long-acting antiretroviral therapy. EcoHIV-infected, athymic mice were more permissive to virus replication in macrophages than were wild-type mice, suffered cognitive dysfunction, as well as increased numbers of monocytes and macrophages infiltrating the brain. Our results suggest an important role of HIV expressing macrophages in HIV neuropathogenesis in hosts with suppressed HIV replication.

Elimination of GPR146-mediated antiviral function through IRF3/HES1-signalling pathway.

As the most important host defence against viral infection, interferon (IFN) stimulates hundreds of antiviral genes (ISGs) that together establish an 'antiviral state'. However, the antiviral function of most ISGs in viral infection still need further exploration. Here, we demonstrated that the expression of G-protein-coupled receptor 146 (GPR146) is highly increased by both IFN-ß and IFN-γ in a signal transducer and activator of transcription 1-dependent signalling pathway. Most importantly, overexpression of GPR146 protects the host cells from vesicular stomatitis virus and Newcastle disease virus infection but not from infection by herpes simplex virus. In contrast, the virus-induced IFN-ß production changed little in Gpr146-knockout cells. Furthermore, the Gpr146-deficient mice showed similar susceptibility to wild-type mice with vesicular stomatitis virus infection. Interestingly, the expression of GPR146 in virus-infected cells was strikingly reduced and can partially explain why the viral infection was little influenced in Gpr146-knockout mice. Surprisingly, virus-activated IFN regulatory factor 3 (IRF3) signalling not only induces the expression of IFN but also represses GPR146 expression through HES1 (hairy and enhancer of split-1)-mediated transcriptional activity to establish a dynamic equilibrium between pro-viral and antiviral stages in host cells. Taken together, these data reveal the antiviral role of GPR146 in fighting viral infection although the GPR146-mediated protection is eliminated by IRF3/HES1-signalling, which suggests a potential therapeutic significance of both GPR146 and HES1 signalling in viral infection.

The effect of Isoprinosine treatment on persistent infection of Balb/c mice infected with murine gammaherpesvirus 68.

We demonstrated the positive effect of Isoprinosine treatment on persistent infection of Balb/c mice with murine gammaherpesvirus 68 (MHV-68). Increased number of leukocytes, increased percentage of neutrophils, elevated levels of virus-neutralizing (VN) antibodies, reduced number of atypical lymphocytes and reduced virus titers were detected in the examined organs after a 14-day treatment. The positive effect of Isoprinosine therapy vanished after 120-150 days. After this interval, we demonstrated lower numbers of leukocytes, lower levels of VN antibodies and an increased number of atypical lymphoid monocytes in the Isoprinosine-treated group. Immunological parameters correlated with increased titers of virus in all investigated organs. Evidence of immunostimulation was demonstrated by lower incidence of tumor formation (7.5%) in the group of MHV-infected and Isoprinosine-treated mice in comparison to group without Isoprinosine treatment (17.5%). The presented results showed that Isoprinosine therapy had a positive impact on persistent infection of mice with MHV-68, but this effect was time-limited. The improvement of the investigated parameters lasted for five months only. Our presented results confirmed that each treatment with Isoprinosine should be repeated and must be long-term in some chronic infections.

Bromodomain protein Brd3 promotes Ifnb1 transcription via enhancing IRF3/p300 complex formation and recruitment to Ifnb1 promoter in macrophages.

As members of bromodomain and extra-terminal motif protein family, bromodomain-containing proteins regulate a wide range of biological processes including protein scaffolding, mitosis, cell cycle progression and transcriptional regulation. The function of these bromodomain proteins (Brds) in innate immune response has been reported but the role of Brd3 remains unclear. Here we find that virus infection significantly downregulate Brd3 expression in macrophages and Brd3 knockout inhibits virus-triggered IFN-ß production. Brd3 interacts with both IRF3 and p300, increases p300-mediated acetylation of IRF3, and enhances the association of IRF3 with p300 upon virus infection. Importantly, Brd3 promotes the recruitment of IRF3/p300 complex to the promoter of Ifnb1, and increases the acetylation of histone3/histone4 within the Ifnb1 promoter, leading to the enhancement of type I interferon production. Therefore, our work indicated that Brd3 may act as a coactivator in IRF3/p300 transcriptional activation of Ifnb1 and provided new epigenetic mechanistic insight into the efficient activation of the innate immune response.

THE STRUCTURAL CHANGES OF MACROPHAGES INFECTED WITH TICK-BORNE ENCEPHALITIS VIRUS.

Macrophages belong to the innate immune cells and play a key role in the pathogenesis of viral infections. The results of ultrastructural study of macrophages infected with tick-borne encephalitis virus (TBEV), the Flavivirus family, pathogens of human infections, affecting the nervous system, were presented. With the assistance of virological methods was found that the TBEV are absorbed by macrophages and replication in them. An ultrastructural study has shown that the virus enters into the cytoplasm by local destruction of plasmalemma and newly synthesized virus particles exited from the cell by same. Simultaneously there is a seal of perinuclear cytoplasm space, where found in a large number of ribosomes, microfilaments, ribonucleoprotein fibers and viral special structure: nucleocapsids, tubular formations and viral layers (fabrics). On the surface of last structures the newly synthesized virus particles were visualized. Thus, the evidence shows that macrophages play a role in the spread of TBEV, being for their the target cell. As active antigen presenting cells the macrophages can modulate the protective response of the body and influence on the pathogenesis of tick-borne encephalitis.

E3 ubiquitin ligase RNF128 promotes innate antiviral immunity through K63-linked ubiquitination of TBK1.

TBK1 is essential for interferon-ß (IFN-ß) production and innate antiviral immunity. Here we identified the T cell anergy-related E3 ubiquitin ligase RNF128 as a positive regulator of TBK1 activation. RNF128 directly interacted with TBK1 through its protease-associated (PA) domain and catalyzed the K63-linked polyubiquitination of TBK1, which led to TBK1 activation, IRF3 activation and IFN-ß production. Deficiency of RNF128 expression attenuated IRF3 activation, IFN-ß production and innate antiviral immune responses to RNA and DNA viruses, in vitro and in vivo. Our study identified RNF128 as an E3 ligase for K63-linked ubiquitination and activation of TBK1 and delineated a previously unrecognized function for RNF128.

Mint3 potentiates TLR3/4- and RIG-I-induced IFN-ß expression and antiviral immune responses.

Type I IFNs (IFN-α/ß) play crucial roles in the elimination of invading viruses. Multiple immune cells including macrophages recognize viral infection through a variety of pattern recognition receptors, such as Toll-like receptors (TLRs) and retinoic acid-inducible gene-I (RIG-I)-like receptors, and initiate type I IFN secretion and subsequent antiviral immune responses. However, the mechanisms by which host immune cells can produce adequate amounts of type I IFNs and then eliminate viruses effectively remain to be further elucidated. In the present study, we show that munc18-1-interacting protein 3 (Mint3) expression can be markedly induced during viral infection in macrophages. Mint3 enhances TLR3/4- and RIG-I-induced IRF3 activation and IFN-ß production by promoting K63-linked polyubiquitination of TNF receptor-associated factor 3 (TRAF3). Consistently, Mint3 deficiency greatly attenuated antiviral immune responses and increased viral replication. Therefore, we have identified Mint3 as a physiological positive regulator of TLR3/4 and RIG-I-induced IFN-ß production and have outlined a feedback mechanism for the control of antiviral immune responses.