Viral RNA detection by RIG-I-like receptors. Curr Opin Immunol. 2015;32:48-53. [PMID: 25594890 DOI: 10.1016/j.coi.2014.12.012]

PTPN2 modulates antiviral immunity in grouper by promoting TBK1 degradation and suppressing interferon signaling

As a member of the class I non-receptor protein tyrosine phosphatase family, Tyrosine-protein phosphatase non-receptor type 2 (PTPN2) plays a pivotal role in the regulation of cellular signaling pathways. In this study, we successfully cloned and characterized a PTPN2 homolog from Epinephelus coioides, designated as EcPTPN2. The open reading frame (ORF) of EcPTPN2 spans 1186 nucleotides, encoding a protein of 395 amino acids (Accession number: PV289599). Sequence analysis revealed that EcPTPN2 contains the conserved PTPc domain and exhibits high sequence homology with Cottoperca gobio (93.40 %) and Chelmon rostratus (92.13 %). EcPTPN2 exhibited ubiquitous expression across all examined tissues, with particularly high expression levels observed in the head kidney, spleen, and brain. Subcellular localization analysis revealed that EcPTPN2 was predominantly localized in the nucleus of grouper spleen (GS) cells. Ectopic expression of EcPTPN2 significantly enhanced the replication of Singapore grouper iridovirus (SGIV) in GS cells. EcPTPN2 was found to modulate the cGAS-STING signaling pathway by attenuating its stimulatory effect on IFN3 promoter activity. EcPTPN2 was demonstrated to interact with EcTBK1 through Co-IP analysis. Ectopic expression of EcPTPN2 facilitated the degradation of exogenous EcTBK1, resulting in a dose-dependent reduction of EcTBK1 protein levels. These findings provide valuable insights into the innate immune mechanisms of grouper against viral infections, offering a molecular basis for understanding host-pathogen interactions in this economically important marine species.

Synergistic Activity of Second Mitochondrial-Derived Activator of Caspases Mimetic with Toll-like Receptor 8 Agonist Reverses HIV-1-Latency and Enhances Antiviral Immunity

HIV-1 infection is successfully treated by antiretroviral therapy; however, it is not curative as HIV-1 remains present in the viral reservoir. A strategy to eliminate the viral reservoir relies on the reactivation of the latent provirus to subsequently trigger immune-mediated clearance. Here, we investigated whether the activation of Toll-like receptor 8 (TLR8) or RIG-I-like receptor (RLR) together with the latency reversal agent (LRA) second mitochondrial-derived activator of caspases mimetics (SMACm) leads to HIV-1 reservoir reduction and antiviral immune activation. The TLR8 and RLR agonist elicited a robust pro-inflammatory cytokine response in PBMCs from both PWH and uninfected people. Notably, co-stimulation with SMACm specifically enhanced TLR8 induced pro-inflammatory cytokine as well as CD8 T cell responses. Ex vivo treatment of PBMCs from PWH with SMACm significantly decreased the size of the inducible HIV-1 reservoir, whereas targeting TLR8 or RLR reduced the HIV-1 reservoir in 50% of PWH ex vivo. Although co-stimulation with TLR8/RLR agonists further reduced the HIV-1 reservoir in 25% of PWH ex vivo, effectively inducing antiviral immunity may help eliminate reactivated HIV-1 cells in vivo. Our findings strongly suggest that LRAs can be used in combination with agonists for pattern recognition receptors to reactivate HIV-1 and induce antiviral immunity.

Tripartite motif 22 (TRIM22) downregulates TLR3-induced CCL5 expression in human renal proximal tubular epithelial cells

BACKGROUND

Tripartite motif 22 (TRIM22) plays a key role in viral defense by suppressing replication. Kidney transplant recipients and patients with chronic kidney disease are compromised hosts and susceptible to viral infections. Although several viruses that infect the renal tubules have been identified, the function and role of TRIM22 in viral infections of the renal tubules remain unknown. Tubular epithelial cells express Toll-like receptors (TLRs), which are pattern recognition receptors. Notably, TLR3 recognizes viral RNA and induces the release of type I interferons (IFNs) and subsequently several proinflammatory chemokines, such as IFN-β and C-C motif chemokine ligand 5 (CCL5). This study investigated the role of TRIM22 in TLR3-induced CCL5 expression in cultured human renal proximal tubular epithelial cells (hRPTECs).

METHODS AND RESULTS

hRPTECs were treated with polyinosinic-polycytidylic acid (poly IC), a ligand for TLR3. Reverse transcription-quantitative polymerase chain reaction was used to analyze mRNA expression, and western blotting and enzyme-linked immunosorbent assays were used to analyze protein expression. Poly IC-induced TRIM22 mRNA and protein expression increased in concentration- and time-dependent manners. Cells were transfected with small interfering RNA against IFN-β or TRIM22 to knock down their respective expression. Knockdown of IFN-β attenuated poly IC-induced TRIM22 mRNA and protein expression. Whereas TRIM22 knockdown upregulated poly IC-induced CCL5 mRNA and protein expression.

CONCLUSION

Our results revealed the TLR3-IFN-β-TRIM22 pathways in hRPTECs. TRIM22 suppressed TLR3-induced CCL5 expression, suggesting that TRIM22 suppresses viral infection-induced excessive inflammation in addition to direct antiviral defense.

Potentiating intratumoral therapy with immune checkpoint inhibitors: shifting the paradigm of multimodality therapeutics

Immune checkpoint inhibitors (ICIs) have revolutionized oncology, yielding remarkable and durable responses in various cancers. However, a significant proportion of patients develop resistance to ICIs. The tumor microenvironment plays a critical role in immunotherapy resistance, characterized by immune cell composition, regulatory factors, and tumor mutational burden. Intratumoral immunotherapy, involving direct injection of immune-activating agents into tumors, holds promise for converting immunologically 'cold' tumors into responsive 'hot' tumors. This review explores the rationale for combining intratumoral therapies (ITs) with ICIs, highlighting their complementary mechanisms of action and clinical effects. Notable IT approaches include oncolytic viruses, toll-like receptor agonists, and stimulator of interferon gene agonists with ICIs. Overall, combining ITs with ICIs offers a rational strategy to potentiate antitumor immune response and overcome resistance. Further research is needed to optimize the combination strategies, identify biomarkers of response, and establish the safety and efficacy of these novel therapeutic approaches.

Helicase protein DDX11 as a novel antiviral factor promoting RIG-I-MAVS-mediated signaling pathway

Type Ι interferon (IFN) production mediated by retinoic acid-inducible gene 1 (RIG-I) and mitochondrial antiviral signaling protein (MAVS) is essential for antiviral innate immune responses. Here, we report the identification of a novel co-sensor for cytosolic nucleic acids: DEAD/H-box helicase 11 (DDX11), a member of the DExD/H (Asp-Glu-x-Asp/His)-box helicase family. Knockdown or knockout of DDX11 attenuated the ability of cells to increase IFN-β, IFN-stimulated gene 56, and C-X-C motif chemokine ligand 10 in response to SeV and poly (I:C) by blocking the activation of TANK-binding kinase 1 and IFN regulatory factor 3. Nucleic acid sensing by DDX11 was independent of the stimulator of IFN genes but was dependent on RIG-I and MAVS. DDX11 regulated RIG-I-MAVS-mediated IFN signaling by specifically interacting with nucleic acid, RIG-I, and MAVS to enhance RIG-I-double-strand RNA and RIG-I-MAVS binding affinity. Overall, our results identified a critical role for DDX11 in the innate immune response and provided molecular insights into the mechanisms by which DDX11 recognized cytosolic nucleic acid and interacted with RIG-Ι and MAVS for potent IFN signaling and antiviral immunity.

IMPORTANCE

Innate immunity is the first and most rapid host defense against virus infection. Recognition of viral RNA by the retinoic acid-inducible gene 1 (RIG-I)-like receptors (RLRs) initiates innate antiviral immune responses. How the binding of viral RNA to and activation of the RLRs are regulated remains enigmatic. In this study, we identified DEAD/H-box helicase 11 (DDX11) as a positive regulator of the RIG-I-mitochondrial antiviral signaling protein (MAVS)-mediated signaling pathways. Mechanistically, we demonstrated that DDX11 bound to viral RNA, interacted with RIG-I, and promoted their binding to viral RNA. DDX11 also promoted the interaction between RIG-I and MAVS and activation of RIG-I-MAVS signaling. Overall, our results elucidate the role of DDX11 in RIG-I-MAVS-dependent signaling pathways and may shed light on innate immune gene regulation.

The RIG-I-like receptor signaling pathway triggered by Staphylococcus aureus promotes breast cancer metastasis

Host microbes are increasingly recognized as key components in various types of cancer, although their exact impact remains unclear. This study investigated the functional significance of Staphylococcus aureus (S. aureus) in breast cancer tumorigenesis and progression. We found that S. aureus invasion resulted in a compromised DNA damage response process, as evidenced by the absence of G1-phase arrest and apoptosis in breast cells in the background of double strand breaks production and the activation of the ataxia-telangiectasia mutated (ATM)-p53 signaling pathway. The high-throughput mRNA sequencing, bioinformatics analysis and pharmacological studies revealed that S. aureus facilitates breast cell metastasis through the innate immune pathway, particularly in cancer cells. During metastasis, S. aureus initially induced the expression of RIG-I-like receptors (RIG-I in normal breast cells, RIG-I and MDA5 in breast cancer cells), which in turn activated NF-κB p65 expression. We further showed that NF-κB p65 activated the CCL5-CCR5 pathway, contributing to breast cell metastasis. Our study provides novel evidence that the innate immune system, triggered by bacterial infection, plays a role in bacterial-driven cancer metastasis.

The multiple roles of interferon regulatory factor family in health and disease

Interferon Regulatory Factors (IRFs), a family of transcription factors, profoundly influence the immune system, impacting both physiological and pathological processes. This review explores the diverse functions of nine mammalian IRF members, each featuring conserved domains essential for interactions with other transcription factors and cofactors. These interactions allow IRFs to modulate a broad spectrum of physiological processes, encompassing host defense, immune response, and cell development. Conversely, their pivotal role in immune regulation implicates them in the pathophysiology of various diseases, such as infectious diseases, autoimmune disorders, metabolic diseases, and cancers. In this context, IRFs display a dichotomous nature, functioning as both tumor suppressors and promoters, contingent upon the specific disease milieu. Post-translational modifications of IRFs, including phosphorylation and ubiquitination, play a crucial role in modulating their function, stability, and activation. As prospective biomarkers and therapeutic targets, IRFs present promising opportunities for disease intervention. Further research is needed to elucidate the precise mechanisms governing IRF regulation, potentially pioneering innovative therapeutic strategies, particularly in cancer treatment, where the equilibrium of IRF activities is of paramount importance.

Cytokine Storm-Induced Thyroid Dysfunction in COVID-19: Insights into Pathogenesis and Therapeutic Approaches

Angiotensin-converting enzyme 2 receptors (ACE2R) are requisite to enter the host cells for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). ACE2R is constitutive and functions as a type I transmembrane metallo-carboxypeptidase in the renin-angiotensin system (RAS). On thyroid follicular cells, ACE2R allows SARS-CoV-2 to invade the thyroid gland, impose cytopathic effects and produce endocrine abnormalities, including stiff back, neck pain, muscle ache, lethargy, and enlarged, inflamed thyroid gland in COVID-19 patients. Further damage is perpetuated by the sudden bursts of pro-inflammatory cytokines, which is suggestive of a life-threatening syndrome known as a "cytokine storm". IL-1β, IL-6, IFN-γ, and TNF-α are identified as the key orchestrators of the cytokine storm. These inflammatory mediators upregulate transcriptional turnover of nuclear factor-kappa B (NF-κB), Janus kinase/signal transducer and activator of transcription (JAK/STAT), and mitogen-activated protein kinase (MAPK), paving the pathway for cytokine storm-induced thyroid dysfunctions including euthyroid sick syndrome, autoimmune thyroid diseases, and thyrotoxicosis in COVID-19 patients. Targeted therapies with corticosteroids (dexamethasone), JAK inhibitor (baricitinib), nucleotide analogue (remdesivir) and N-acetyl-cysteine have demonstrated effectiveness in terms of attenuating the severity and frequency of cytokine storm-induced thyroid dysfunctions, morbidity and mortality in severe COVID-19 patients. Here, we review the pathogenesis of cytokine storms and the mechanisms and pathways that establish the connection between thyroid disorder and COVID-19. Moreover, cross-talk interactions of signalling pathways and therapeutic strategies to address COVID-19-associated thyroid diseases are also discussed herein.

Singapore grouper iridovirus VP128 inhibits STING-TBK1 mediated signaling to evade antiviral immunity

Singapore grouper iridovirus (SGIV) belongs to the family Iridoviridae and the genus Ranavirus, which is a large cytoplasmic DNA virus. Infection of grouper with SGIV can cause hemorrhage and swelling of the spleen of the fish. Previous work on genome annotation demonstrated that SGIV contained numerous uncharacterized or hypothetical open reading frames (ORFs), whose functions remained largely unknown. In the present study, the protein encoded by SGIV ORF128 (VP128) was identified. VP128 is predominantly localized within the endoplasmic reticulum (ER). Overexpression of VP128 significantly promoted SGIV replication. VP128 inhibited the interferon (IFN)-3 promoter activity and mRNA level of IFN-related genes induced by poly(I:C), Epinephelus coioides cyclic GMP/AMP synthase (EccGAS)/stimulator of IFN genes (EcSTING), and TANK-binding kinase 1 (EcTBK1). Moreover, VP128 interacted with EcSTING and EcTBK1. The interaction between VP128 and EcSTING was independent of any specific structural domain of EcSTING. Together, our results demonstrated that SGIV VP128 negatively regulated the IFN response by inhibiting EcSTING-EcTBK1 signaling for viral evasion.

Grouper OTUB1 and OTUB2 promote red-spotted grouper nervous necrosis virus (RGNNV) replication by inhibiting the host innate immune response

Red-spotted grouper nervous necrosis virus (RGNNV) is a major viral pathogen of grouper and is able to antagonize interferon responses through multiple strategies, particularly evading host immune responses by inhibiting interferon responses. Ovarian tumor (OTU) family proteins are an important class of DUBs and the underlying mechanisms used to inhibit interferon pathway activation are unknown. In the present study, primers were designed based on the transcriptome data, and the ovarian tumor (OTU) domain-containing ubiquitin aldehyde-binding protein 1 (OTUB1) and OTUB2 genes of Epinephelus coioides (EcOTUB1 and EcOTUB2) were cloned and characterized. The homology alignment showed that both EcOTUB1 and EcOTUB2 were most closely related to E. lanceolatus with 98 % identity. Both EcOTUB1 and EcOTUB2 were distributed to varying degrees in grouper tissues, and the transcript levels were significantly up-regulated following RGNNV stimulation. Both EcOTUB1 and EcOTUB2 promoted replication of RGNNV in vitro, and inhibited the promoter activities of interferon stimulated response element (ISRE), nuclear transcription factors kappaB (NF-κB) and IFN3, and the expression levels of interferon related genes and proinflammatory factors. Co-immunoprecipitation experiments showed that both EcOTUB1 and EcOTUB2 could interact with TRAF3 and TRAF6, indicating that EcOTUB1 and EcOTUB2 may play important roles in interferon signaling pathway. The results will provide a theoretical reference for the development of novel disease prevention and control techniques.

Nervous necrosis virus capsid protein and Protein A dynamically modulate the fish cGAS-mediated IFN signal pathway to facilitate viral evasion

Nervous necrosis virus (NNV), an aquatic RNA virus belonging to Betanodavirus, infects a variety of marine and freshwater fishes, leading to massive mortality of cultured larvae and juveniles and substantial economic losses. The enzyme cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) is widely recognized as a central component in the innate immune response to cytosolic DNA derived from different pathogens. However, little is known about the response of cGAS to aquatic RNA viruses. This study found that Epinephelus coioides cGAS (EccGAS) overexpression inhibited NNV replication, whereas EccGAS silencing promoted NNV replication. The anti-NNV activity of EccGAS was involved in interferon (IFN) signaling activation including tumor necrosis factor receptor-associated factor family member-associated NF-kappa-B activator-binding kinase 1 (TBK1) phosphorylation, interferon regulatory factor 3 (IRF3) nuclear translocation, and the subsequent induction of IFNc and ISGs. Interestingly, NNV employed its capsid protein (CP) or Protein A (ProA) to negatively or positively modulate EccGAS-mediated IFN signaling by simultaneously targeting EccGAS. CP interacted with EccGAS via the arm-P, S-P, and SD structural domains and promoted its polyubiquitination with K48 and K63 linkages in an EcUBE3C (the ubiquitin ligase)-dependent manner, ultimately leading to EccGAS degradation. Conversely, ProA bound to EccGAS and inhibited its ubiquitination and degradation. In regulating EccGAS protein content, CP's inhibitory action was more pronounced than ProA's protective effect, allowing successful NNV replication. These novel findings suggest that NNV CP and ProA dynamically modulate the EccGAS-mediated IFN signaling pathway to facilitate the immune escape of NNV. Our findings shed light on a novel mechanism of virus-host interaction and provide a theoretical basis for the prevention and control of NNV.IMPORTANCEAs a well-known DNA sensor, cGAS is a pivotal component in innate anti-viral immunity to anti-DNA viruses. Although there is growing evidence regarding the function of cGAS in the resistance to RNA viruses, the mechanisms by which cGAS participates in RNA virus-induced immune responses in fish and how aquatic viruses evade cGAS-mediated immune surveillance remain elusive. Here, we investigated the detailed mechanism by which EccGAS positively regulates the anti-NNV response. Furthermore, NNV CP and ProA interacted with EccGAS, regulating its protein levels through ubiquitin-proteasome pathways, to dynamically modulate the EccGAS-mediated IFN signaling pathway and facilitate viral evasion. Notably, NNV CP was identified to promote the ubiquitination of EccGAS via ubiquitin ligase EcUBE3C. These findings unveil a novel strategy for aquatic RNA viruses to evade cGAS-mediated innate immunity, enhancing our understanding of virus-host interactions.

Soluble form of the MDA5 protein in human sera

Viral double-stranded RNA (dsRNA) is sensed by toll-like receptor 3 (TLR3) and retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), including melanoma differentiation-associated gene 5 (MDA5). MDA5 recognizes the genome of dsRNA viruses and replication intermediates of single-stranded RNA viruses. MDA5 also plays an important role in the development of autoimmune diseases, such as Aicardi-Goutieres syndrome and type I diabetes. Patients with dermatomyositis with serum MDA5 autoantibodies (anti-CADM-140) are known to have a high risk of developing rapidly progressive interstitial lung disease and poor prognosis. However, there have been no reports on the soluble form of MDA5 in human serum. In the present study, we generated in-house monoclonal antibodies (mAbs) against human MDA5. We then performed immunohistochemical analysis and sensitive sandwich immunoassays to detect the MDA5 protein using two different mAbs (clones H27 and H46). As per the immunohistochemical analysis, the MDA5 protein was moderately expressed in the alveolar epithelia of normal lungs and was strongly expressed in the cytoplasm of lymphoid cells in the tonsils and acinar cells of the pancreas. Interestingly, soluble MDA5 protein was detectable in the serum, but not in the urine, of healthy donors. Soluble MDA5 protein was also detectable in the serum of patients with dermatomyositis. Immunoblot analysis showed that human cells expressed a 120 kDa MDA5 protein, while the 60 kDa MDA5 protein increased in the supernatant of peripheral mononuclear cells within 15 min after MDA5 agonist/double-strand RNA stimulation. Hydrogen deuterium exchange mass spectrometry revealed that an anti-MDA5 mAb (clone H46) bound to the epitope (415QILENSLLNL424) derived from the helicase domain of MDA5. These results indicate that a soluble MDA5 protein containing the helicase domain of MDA5 could be rapidly released from the cytoplasm of tissues after RNA stimulation.

LGP2 Facilitates Bacterial Escape through Binding Peptidoglycan via EEK Motif and Suppressing NOD2-RIP2 Axis in Cyprinidae and Xenocyprididae Families

RIG-I-like receptors and NOD-like receptors play pivotal roles in recognizing microbe-associated molecular patterns and initiating immune responses. The LGP2 and NOD2 proteins are important members of the RIG-I-like receptor and NOD-like receptor families, recognizing viral RNA and bacterial peptidoglycan (PGN), respectively. However, in some instances bacterial infections can induce LPG2 expression via a mechanism that remains largely unknown. In the current study, we found that LGP2 can compete with NOD2 for PGN binding and inhibit antibacterial immunity by suppressing the NOD2-RIP2 axis. Recombinant CiLGP2 (Ctenopharyngodon idella LGP2) produced using either prokaryotic or eukaryotic expression platform can bind PGN and bacteria in pull-down and ELISA assays. Comparative protein structure models and intermolecular interaction prediction calculations as well as pull-down and colocalization experiments indicated that CiLGP2 binds PGN via its EEK motif with species and structural specificity. EEK deletion abolished PGN binding of CiLGP2, but insertion of the CiLGP2 EEK motif into zebrafish and mouse LGP2 did not confer PGN binding activity. CiLGP2 also facilitates bacterial replication by interacting with CiNOD2 to suppress expression of NOD2-RIP2 pathway genes. Sequence analysis and experimental verification demonstrated that LGP2 having EEK motif that can negatively regulate antibacterial immune function is present in Cyprinidae and Xenocyprididae families. These results show that LGP2 containing EEK motif competes with NOD2 for PGN binding and suppresses antibacterial immunity by inhibiting the NOD2-RIP2 axis, indicating that LGP2 plays a crucial negative role in antibacterial response beyond its classical regulatory function in antiviral immunity.

Plasminogen activator urokinase interacts with the fusion protein and antagonizes the growth of Peste des petits ruminants virus

Peste des petits ruminants is an acute and highly contagious disease caused by the Peste des petits ruminants virus (PPRV). Host proteins play a crucial role in viral replication. However, the effect of fusion (F) protein-interacting partners on PPRV infection is poorly understood. In this study, we found that the expression of goat plasminogen activator urokinase (PLAU) gradually decreased in a time- and dose-dependent manner in PPRV-infected goat alveolar macrophages (GAMs). Goat PLAU was subsequently identified using co-immunoprecipitation and confocal microscopy as an F protein binding partner. The overexpression of goat PLAU inhibited PPRV growth and replication, whereas silencing goat PLAU promoted viral growth and replication. Additionally, we confirmed that goat PLAU interacted with a virus-induced signaling adapter (VISA) to antagonize F-mediated VISA degradation, increasing the production of type I interferon. We also found that goat PLAU reduced the inhibition of PPRV replication in VISA-knockdown GAMs. Our results show that the host protein PLAU inhibits the growth and replication of PPRV by VISA-triggering RIG-I-like receptors and provides insight into the host protein that antagonizes PPRV immunosuppression.IMPORTANCEThe role of host proteins that interact with Peste des petits ruminants virus (PPRV) fusion (F) protein in PPRV replication is poorly understood. This study confirmed that goat plasminogen activator urokinase (PLAU) interacts with the PPRV F protein. We further discovered that goat PLAU inhibited PPRV replication by enhancing virus-induced signaling adapter (VISA) expression and reducing the ability of the F protein to degrade VISA. These findings offer insights into host resistance to viral invasion and suggest new strategies and directions for developing PPR vaccines.

Regulation of type I and type III interferon induction in response to pathogen sensing

Type I and III interferons (IFN-I and IFN-III) have a central role in the early antimicrobial response against invading pathogens. Induction of IFN-Is and IFN-IIIs arises due to the sensing by pattern recognition receptors of pathogen-associated molecular patterns (from micro-organisms) or of damage-associated molecular patterns (DAMPs; produced by host cells). Here, we review recent developments on how IFN-I and IFN-III expression is stimulated by different pathogens and how the signalling pathways leading to IFN induction are tightly regulated. We also summarise the growing knowledge of the sensing pathways that lead to IFN-I and IFN-III induction in response to severe acute respiratory syndrome coronavirus 2.

Radiotherapy Combined with Intralesional Immunostimulatory Agents for Soft Tissue Sarcomas

Immunotherapy has shifted the treatment paradigm for many types of cancer. Unfortunately, the most commonly used immunotherapies, such as immune checkpoint inhibitors (ICI), have yielded limited benefit for most types of soft tissue sarcoma (STS). Radiotherapy (RT) is a mainstay of sarcoma therapy and can induce immune modulatory effects. Combining immunotherapy and RT in STS may be a promising strategy to improve sarcoma response to RT and increase the efficacy of immunotherapy. Most combination strategies have employed immunotherapies, such as ICI, that derepress immune suppressive networks. These have yielded only modest results, possibly due to the limited immune stimulatory effects of RT. Combining RT with immune stimulatory agents has yielded promising preclinical and clinical results but can be limited by the toxic nature of systemic administration of immune stimulants. Using intralesional immune stimulants may generate stronger RT immune modulation and less systemic toxicity, which may be a feasible strategy in accessible tumors such as STS. In this review, we summarize the immune modulatory effects of RT, the mechanism of action of various immune stimulants, including toll-like receptor agonists, and data for combinatorial strategies utilizing these agents.

Signaling pathways regulating the immune function of cochlear supporting cells and their involvement in cochlear pathophysiology

The inner ear, including the cochlea, used to be regarded as an immune-privileged site because of its immunologically isolated environment caused by the blood-labyrinthine barrier. Cochlear resident macrophages, which originate from the yolk sac or fetal liver during the embryonic stage and are maintained after birth, are distributed throughout various regions of the cochlear duct. Intriguingly, these cells are absent in the organ of Corti, where hair cells (HCs) and supporting cells (SCs) are located, except for a limited number of ionized calcium-binding adapter molecule 1 (Iba1)-positive cells. Instead, SCs exert glial functions varying from a quiescent to an emergency state. Notably, SCs acquire the nature of macrophages and begin to secrete inflammatory cytokines during viral infection in the organ of Corti, which is ostensibly unprotected owing to the lack of general resident macrophages. This review provides an overview of both positive and negative functions of SCs enabled to acquire macrophage phenotypes upon viral infection focusing on the signaling pathways that regulate these functions. The former function protects HCs from viral infection by inducting type I interferons, and the latter function induces HC death by necroptosis, leading to sensorineural hearing loss. Thus, SCs play contradictory roles as immune cells with acquired macrophage phenotypes; thereby, they are favorable and unfavorable to HCs, which play a pivotal role in hearing function.

Immunosuppressive effects of the mycotoxin patulin in macrophages

Patulin (PAT) is a fungi-derived secondary metabolite produced by numerous fungal species, especially within Aspergillus, Byssochlamys, and Penicillium genera, amongst which P. expansum is the foremost producer. Similar to other fungi-derived metabolites, PAT has been shown to have diverse biological features. Initially, PAT was used as an effective antimicrobial agent against Gram-negative and Gram-positive bacteria. Then, PAT has been shown to possess immunosuppressive properties encompassing humoral and cellular immune response, immune cell function and activation, phagocytosis, nitric oxide and reactive oxygen species production, cytokine release, and nuclear factor-κB and mitogen-activated protein kinases activation. Macrophages are a heterogeneous population of immune cells widely distributed throughout organs and connective tissue. The chief function of macrophages is to engulf and destroy foreign bodies through phagocytosis; this ability was fundamental to his discovery. However, macrophages play other well-established roles in immunity. Thus, considering the central role of macrophages in the immune response, we review the immunosuppressive effects of PAT in macrophages and provide the possible mechanisms of action.

Exploring type I interferon pathway: virulent vs. attenuated strain of African swine fever virus revealing a novel function carried by MGF505-4R

African swine fever virus represents a significant reemerging threat to livestock populations, as its incidence and geographic distribution have surged over the past decade in Europe, Asia, and Caribbean, resulting in substantial socio-economic burdens and adverse effects on animal health and welfare. In a previous report, we described the protective properties of our newly thermo-attenuated strain (ASFV-989) in pigs against an experimental infection of its parental Georgia 2007/1 virulent strain. In this new study, our objective was to characterize the molecular mechanisms underlying the attenuation of ASFV-989. We first compared the activation of type I interferon pathway in response to ASFV-989 and Georgia 2007/1 infections, employing both in vivo and in vitro models. Expression of IFN-α was significantly increased in porcine alveolar macrophages infected with ASFV-989 while pigs infected with Georgia 2007/1 showed higher IFN-α than those infected by ASFV-989. We also used a medium-throughput transcriptomic approach to study the expression of viral genes by both strains, and identified several patterns of gene expression. Subsequently, we investigated whether proteins encoded by the eight genes deleted in ASFV-989 contribute to the modulation of the type I interferon signaling pathway. Using different strategies, we showed that MGF505-4R interfered with the induction of IFN-α/β pathway, likely through interaction with TRAF3. Altogether, our data reveal key differences between ASFV-989 and Georgia 2007/1 in their ability to control IFN-α/β signaling and provide molecular mechanisms underlying the role of MGF505-4R as a virulence factor.

Global trends in research of melanoma differentiation-associated gene 5: a bibliometric analysis from 2002 to 2022

BACKGROUND

Melanoma differentiation-associated gene 5 (MDA5), as a cytoplasmic sensor for viral double-stranded RNAs, has received increasing attention in recent years. Although considerable headway has been made on the functional role of MDA5 in antiviral immunity and autoimmune disease, the available literature is insufficient to assess the vast field.

METHODS

This study performed a bibliometric analysis to investigate current hotspots in the global scientific output of MDA5 over the past two decades. Related publications and recorded information from 2002 to 2022 in the Web of Science Core Collection (WoSCC) database were retrieved. VOSviewer and CiteSpace were used for quantitative evaluation and visualization.

RESULTS

A total of 2267 original articles and reviews were obtained, and the annual number of publications related to MDA5 was increasing rapidly. China has published the most papers, while the USA was the most influential country with the most citations and the highest H-index. The Chinese Academy of Sciences, the United States Department of Health and Human Services, and the Journal of Virology were the most prolific research affiliation, funding source, and journal, respectively. Fujita T (Kyoto University) was the most productive author with the highest H-index and had close cooperation with Kato H and Yoneyama M. The keywords "RIG-I," "MDA5," "innate immunity," "double-stranded-RNA," and "recognition" had the highest frequency, while "dermatomyositis" as well as "autoantibody" seemed to be the emerging hotspots.

CONCLUSION

This study comprehensively demonstrated the research frontiers of MDA5 and will provide a useful resource for scholars to conduct future decisions.

KEY POINTS

We conducted the first in-depth survey of the research frontiers on melanoma differentiation-associated gene 5 (MDA5) over the past two decades via bibliometric analysis. We found that many early breakthroughs have been made in the mechanism of MDA5-mediated antiviral immune responses, and the role of MDA5 in autoimmune and autoinflammatory diseases has raised the recent concern. We identified that the virus infection-associated pathogenesis and effective therapeutic strategy of anti-MDA5 antibody-positive dermatomyositis will remain the hotspots in the future.

Innate immune response to double-stranded RNA in American heritage chicken breeds

Backyard poultry flocks that employ heritage breeds of chicken play a crucial role in the maintenance of poultry pathogens of economic and zoonotic importance. This study examined innate immunity to viral pathogens in heritage chicken breeds using a model of viral double-stranded RNA (dsRNA). Following intraperitoneal injection of high molecular weight (HMW) -poly(I:C)/Lyovec into 4-wk-old chicks, we evaluated gene expression in peripheral blood mononuclear cells (PBMCs) and splenocytes. There was a significant difference across breeds in the expression of IL-4, IL-12p40, IFNγ, and B-cell activating factor (BAFF) in the spleen. In PBMCs, a significant difference in IFN-α expression was seen across breeds. Approximately 57% of IFN-α transcripts in PBMCs was explained by levels of expression of MDA5 transcripts. Using flow cytometry, we showed that only monocytes/macrophages (KUL01+ cells) expressed the scavenger receptor CD163. Regression analysis showed that 42% of fold change in CD163 expression on PBMCs was explained by breed (P < 0.0004). In general, breeds that responded to HMW-poly(I:C) by showing higher upregulation of IFNγ, IL-1β, and IL-12p40 transcripts in the spleen, and higher IFNα transcripts in peripheral blood, expressed less CD163 on blood monocytes. These findings suggest a genetic basis for the response of chickens to double-stranded RNA. Surface expression of the scavenger receptor CD163 in PBMCs following injection of high molecular weight poly(I:C) may be a rapid method to select chickens for breeding based on innate immune response to viral dsRNA.

Targeting cap1 RNA methyltransferases as an antiviral strategy

Methylation is one of the critical modifications that regulates numerous biological processes. Guanine capping and methylation at the 7th position (m7G) have been shown to mature mRNA for increased RNA stability and translational efficiency. The m7G capped cap0 RNA remains immature and requires additional methylation at the first nucleotide (N1-2'-O-Me), designated as cap1, to achieve full maturation. This cap1 RNA with N1-2'-O-Me prevents its recognition by innate immune sensors as non-self. Viruses have also evolved various strategies to produce self-like capped RNAs with the N1-2'-O-Me that potentially evades the antiviral response and establishes an efficient replication. In this review, we focus on the importance of the presence of N1-2'-O-Me in viral RNAs and discuss the potential for drug development by targeting host and viral N1-2'-O-methyltransferases.

Function analysis of fish PACT gene in response to virus infection

PACT (interferon-inducible double-stranded RNA-dependent protein kinase activator A) is a cellular protein which can activate PKR in dsRNA-independent manner. However, the role of PACT in fish virus infection remains largely unknown. In this study, a PACT homologue from grouper (Epinephelus coioides)(EcPACT) was cloned and characterized. The open reading frame of EcPACT has a full length of 924 bp and encodes a protein of 307 amino acids with a predicted molecular weight of 33.29 kDa. Similar to mammals, EcPACT contains three dsRBD domains. EcPACT shares 99.67 % homology with E. lanceolatus. Real-time fluorescence quantitative PCR results showed that EcPACT mRNA was widely expressed in all tissues and abundantly expressed in brain, blood, head kidney and kidney. In addition, SGIV and RGNNV infection significantly upregulated the transcript levels of EcPACT. Subcellular localization analysis showed that EcPACT was mainly distributed in the nucleus. Overexpression of EcPACT inhibited the replication of SGIV and RGNNV in vitro and positively regulated the expression of interferon (IFN) and pro-inflammatory factors. The results provide a better understanding of the relationship between PACT and viral infection in fish.

Endosomal Toll-Like Receptors as Therapeutic Targets for Autoimmune Diseases

Nucleic acid (NA)-sensing Toll-like receptors (TLRs) reside in the endosomal compartment of innate immune cells, such as macrophages and dendritic cells. NAs transported to the endosomal compartment are degraded by DNases and RNases. Degradation products, including single-stranded DNA, oligoRNA, and nucleosides, are recognized by TLR7, TLR8, and TLR9 to drive the defense responses against pathogens. NA degradation influences endosomal TLR responses by generating and degrading TLR ligands. TLR ligand accumulation because of impaired NA degradation causes constitutive TLR activation, leading to autoinflammatory and autoimmune diseases. Furthermore, some genes associated with these diseases promote endosomal TLR responses. Therefore, endosomal TLRs are promising therapeutic targets for TLR-mediated inflammatory diseases, and novel drugs targeting TLRs are being developed.

Autophagy as a dual-faced host response to viral infections

Autophagy selectively degrades viral particles or cellular components, either facilitating or inhibiting viral replication. Conversely, most viruses have evolved strategies to escape or exploit autophagy. Moreover, autophagy collaborates with the pattern recognition receptor signaling, influencing the expression of adaptor molecules involved in the innate immune response and regulating the expression of interferons (IFNs). The intricate relationship between autophagy and IFNs plays a critical role in the host cell defense against microbial invasion. Therefore, it is important to summarize the interactions between viral infections, autophagy, and the host defense mechanisms against viruses. This review specifically focuses on the interactions between autophagy and IFN pathways during viral infections, providing a comprehensive summary of the molecular mechanisms utilized or evaded by different viruses.

Sodium Butyrate Induced Neural Stem/Progenitor Cell Death in an Experimental Model of Japanese Encephalitis

The anti-inflammatory and neuroprotective effects of short chain fatty acid (SCFA) butyrate have been explored in a wide array of neurological pathologies. It is a 4-carbon SCFA produced from the fermentation of dietary fibers by the gut-microbiota. As evident from previous literature, butyrate plays a wide array of functions in CNS and interestingly enhances the differentiation potential of Neural stem/Progenitor Cells (NSPCs). Japanese encephalitis virus (JEV) is a well-known member of the Flaviviridae family and has been shown to alter neural stem cell pool of the brain, causing devastating consequences. In this study, we administered sodium butyrate (NaB) post JEV infection in BALB/c mouse model to examine any possible amelioration of the viral infection in NSPCs. In addition, ex vivo neurospheres and in vitro model of NSPCs were also used to study the effect of sodium butyrate in JEV infection. As an unprecedented finding, butyrate treated infected animals presented early onset of symptoms, as compared to their respective JEV infected groups. Alongside, we observed an increased viral load in NSPCs isolated from these animals as well as in cell culture models upon sodium butyrate treatment. Cytometric bead array analysis also revealed an increase in inflammatory cytokines, particularly, MCP-1 and IL-6. Further, increased expression of the key members of the canonical NF-κB pathway, viz-a-viz p-NF-κB, p-Iκ-Bα and p-IKK was observed. Overall, the increased inflammation and cell death caused early symptom progression in NaB-treated JEV infected animal model, which is contradictory to the well documented protective nature of NaB and therefore a better understanding of SCFA-based modulation of the gut-brain axis in viral infections is required.

The immunostimulant effects of the rice ragged stunt virus genome on the growth and metastasis of breast cancer in mouse model

There are multiple treatment strategies that have been reported for breast cancer, while new and effective therapies against it are still necessary. Stimulating the immune system and its components against cancer cells is one of the unique treatment strategies of immunotherapy and long dsRNAs are immunostimulant in this regard. Based on bioinformatics approaches, a fragment of the Rice ragged stunt RNA virus genome was selected and synthesized according to its immunogenicity. Based on the in vitro transcription technique, dsRNA was synthesized and its binding ability to the PEI/PEI-Ac Polyethylenimine (PEI) or Acetylated polyethylenimine (PEI-Ac) was verified by the gel retardation assay. Then, the PEI-Ac was synthesized by adding acetyl groups to the PEI, and the results of the 1H NMR method indicated its successful synthesis. After cancer induction by 4 T1 cells in Balb/C mice, intraperitoneal (IP) and intratumoral (IT) treatment by the PEI/PEI-Ac-dsRNA were performed and the tumor growth inhibition was evaluated. Results demonstrated that PEI/PEI-Ac-dsRNA can lead to a decrease in tumor weight and volume in both the IP and IT routes. Also, by using macro-metastatic nodule counting and hematoxylin and eosin (H&E) staining we showed that PEI/PEI-Ac-dsRNA can prevent micro and macro-metastasis in the lung. Therefore, the PEI/PEI-Ac-dsRNA acts as an effective inhibitor of growth and metastasis of the breast cancer models. We showed that viral dsRNA can exert its antitumor properties by stimulating TNF-α and IFN-γ. In general, our results revealed that dsRNA derived from the plant virus genome stimulates the intrinsic immune system and can be a potential immune stimulant drug for cancer treatment.

TBK1-stabilized ZNF268a recruits SETD4 to methylate TBK1 for efficient interferon signaling

Sufficient activation of interferon signaling is critical for the host to fight against invading viruses, in which post-translational modifications have been demonstrated to play a pivotal role. Here, we demonstrate that the human KRAB-zinc finger protein ZNF268a is essential for virus-induced interferon signaling. We find that cytoplasmic ZNF268a is constantly degraded by lysosome and thus remains low expressed in resting cell cytoplasm. Upon viral infection, TBK1 interacts with cytosolic ZNF268a to catalyze the phosphorylation of Serine 178 of ZNF268a, which prevents the degradation of ZNF268a, resulting in the stabilization and accumulation of ZNF268a in the cytoplasm. Furthermore, we provide evidence that stabilized ZNF268a recruits the lysine methyltransferase SETD4 to TBK1 to induce the mono-methylation of TBK1 on lysine 607, which is critical for the assembly of the TBK1 signaling complex. Notably, ZNF268 S178 is conserved among higher primates but absent in rodents. Meanwhile, rodent TBK1 607th aa happens to be replaced by arginine, possibly indicating a species-specific role of ZNF268a in regulating TBK1 during evolution. These findings reveal novel functions of ZNF268a and SETD4 in regulating antiviral interferon signaling.

Molecular and functional characterization of golden pompano (Trachinotus blochii) TBK1 on IFN regulation

The golden pompano (Trachinotus blochii), a pivotal commercial marine species in China, has gained significant popularity worldwide. However, accompanied with rapid growth and high density aquaculture, golden pompano has been seriously threatened by Nervous necrosis virus (NNV), while its molecular biology research regarding the innate immune system remains unexplored, which is crucial for understanding the activation of interferon (IFN) production and antiviral responses. In this study, we aimed to identify the characterization and function of golden pompano TANK-binding kinase 1 (gpTBK1), thereby providing evidence of the conservation of this classical factor in the RLR pathway among marine fish. Initially, we found the expression of gpTBK1 upregulation in diseased golden pompano with NNV infection and we successfully cloned the full-length open reading frame (ORF) of gpTBK1, consisting of 2172 nucleotides encoding 723 amino acids, from the head kidney. Subsequent analysis of the amino acid sequence revealed homology between gpTBK1 and other fish TBK1 proteins, with conserved N-terminal Serine/Threonine protein kinases catalytic domain (S_TKc) and C-terminal coiled coil domain (CCD). Moreover, the expression pattern showed that gpTBK1 exhibited ubiquitous expression across all evaluated tissues. Furthermore, functional identification experiments indicated that gpTBK1 activated interferon promoters' activity in golden pompano and induced the expression of downstream IFN-stimulated genes (ISGs). Notably, gpTBK1 was found to co-localize and interact with gpIRF3 in the cytoplasm. Collectively, these data provide a comprehensive analysis of the characterization and functional role of gpTBK1 in promoting interferon production. This research may facilitate the further study of the innate antiviral response, particularly the anti-NNV mechanisms, in golden pompano.

Synthesis and pharmacodynamic evaluation of naphthalene derivatives against influenza A virus in vitro and in vivo

Influenza A virus is a highly mutable pathogenic pathogen that could cause a global pandemic. It is necessary to find new anti-influenza drugs to resist influenza epidemics due to the seasonal popularity of a certain area every year. Naphthalene derivatives had potential antiviral activity. A series of naphthalene derivatives were synthesized via the metal-free intramolecular hydroarylation reactions of alkynes. Evaluation of their biological efficacy showed that compound 2-aminonaphthalene 4d had better antiviral activity in vitro than ribavirin. By studying the mechanism of action of 2-aminonaphthalene 4din vivo and in vitro, we found that 4d had antiviral activity to three different subtype influenza viruses of A/Weiss/43 (H1N1), A/Virginia/ATCC2/2009 (H1N1) and A/California/2/2014 (H3N2). Compound 4d had the best effect after viral adsorption, and mainly played in the early stage of virus replication. 2-Aminonaphthalene 4d could reduce the replication of virus by inhibiting the NP and M proteins of virus. Compound 4d cut down ROS accumulation, autophagy and apoptosis induced by influenza virus. Inflammatory response mediated by RIG-1 pathway were suppressed in the cell and mice. In addition, the pathological changes of lung tissue and virus titer in mice were reduced by the administration of 4d. Therefore, naphthalene derivative 4d is a potential drug for the treatment of influenza A virus infection.

Protection of eIF2B from inhibitory phosphorylated eIF2: A viral strategy to maintain mRNA translation during the PKR-triggered integrated stress response

The integrated stress response (ISR) protects cells from a variety of insults. Once elicited (e.g., by virus infections), it eventually leads to the block of mRNA translation. Central to the ISR are the interactions between translation initiation factors eIF2 and eIF2B. Under normal conditions, eIF2 drives the initiation of protein synthesis through hydrolysis of GTP, which becomes replenished by the guanine nucleotide exchange factor eIF2B. The antiviral branch of the ISR is activated by the RNA-activated kinase PKR which phosphorylates eIF2, thereby converting it into an eIF2B inhibitor. Here, we describe the recently solved structures of eIF2B in complex with eIF2 and a novel escape strategy used by viruses. While unphosphorylated eIF2 interacts with eIF2B in its "productive" conformation, phosphorylated eIF2 [eIF2(αP)] engages a different binding cavity on eIF2B and forces it into the "nonproductive" conformation that prohibits guanine nucleotide exchange factor activity. It is well established that viruses express so-called PKR antagonists that interfere with double-strand RNA, PKR itself, or eIF2. However recently, three taxonomically unrelated viruses were reported to encode antagonists targeting eIF2B instead. For one antagonist, the S segment nonstructural protein of Sandfly fever Sicilian virus, atomic structures showed that it occupies the eIF2(αP)-binding cavity on eIF2B without imposing a switch to the nonproductive conformation. S segment nonstructural protein thus antagonizes the activity of PKR by protecting eIF2B from inhibition by eIF2(αP). As the ISR and specifically eIF2B are central to neuroprotection and a wide range of genetic and age-related diseases, these developments may open new possibilities for treatments.

Functional comparisons of the virus sensor RIG-I from humans, the microbat Myotis daubentonii, and the megabat Rousettus aegyptiacus, and their response to SARS-CoV-2 infection

IMPORTANCE

A common hypothesis holds that bats (order Chiroptera) are outstanding reservoirs for zoonotic viruses because of a special antiviral interferon (IFN) system. However, functional studies about key components of the bat IFN system are rare. RIG-I is a cellular sensor for viral RNA signatures that activates the antiviral signaling chain to induce IFN. We cloned and functionally characterized RIG-I genes from two species of the suborders Yangochiroptera and Yinpterochiroptera. The bat RIG-Is were conserved in their sequence and domain organization, and similar to human RIG-I in (i) mediating virus- and IFN-activated gene expression, (ii) antiviral signaling, (iii) temperature dependence, and (iv) recognition of RNA ligands. Moreover, RIG-I of Rousettus aegyptiacus (suborder Yinpterochiroptera) and of humans were found to recognize SARS-CoV-2 infection. Thus, members of both bat suborders encode RIG-Is that are comparable to their human counterpart. The ability of bats to harbor zoonotic viruses therefore seems due to other features.

Structural Investigations of Interactions between the Influenza a Virus NS1 and Host Cellular Proteins

The Influenza A virus is a continuous threat to public health that causes yearly epidemics with the ever-present threat of the virus becoming the next pandemic. Due to increasing levels of resistance, several of our previously used antivirals have been rendered useless. There is a strong need for new antivirals that are less likely to be susceptible to mutations. One strategy to achieve this goal is structure-based drug development. By understanding the minute details of protein structure, we can develop antivirals that target the most conserved, crucial regions to yield the highest chances of long-lasting success. One promising IAV target is the virulence protein non-structural protein 1 (NS1). NS1 contributes to pathogenicity through interactions with numerous host proteins, and many of the resulting complexes have been shown to be crucial for virulence. In this review, we cover the NS1-host protein complexes that have been structurally characterized to date. By bringing these structures together in one place, we aim to highlight the strength of this field for drug discovery along with the gaps that remain to be filled.

Synthesis and evaluation of alkoxy-substituted enamides against influenza A virus in vitro and in vivo

Alkoxy-substituted enamides are often used as synthetic intermediates due to their special reactivity. To the best our knowledge, the biological activity of alkoxy-substituted amines has never been reported so far. We have synthesized a series of alkoxy-substituted enamides to study their anti-influenza A virus activity in vitro and in vivo. Among these compounds, compound E-2o had the best antiviral activity (EC50 = 2.76 ± 0.67 μM) and low cytotoxicity (CC50 = 662.87 ± 24.85 μM). The mechanism of action of this compound was preliminarily explored by us. It alleviated the cytopathic effects and cell death caused by different subtypes of influenza A virus. Different drug delivery methods and timed dosing experiments had shown that E-2o had the best therapeutic effect and mainly played a role in the early stages of virus replication. The expansion of influenza viruses in cells was inhibited by reducing ROS accumulation, cell apoptosis, and autophagy. Alkoxy-substituted enamide E-2o reduced the production of interferon and other pro-inflammatory factors in the RIG-Ⅰ pathway and its downstream NF-κB was induced by influenza A virus in vitro and in vivo. It avoided damage in the mice which was caused by excessive inflammatory factors. In addition, the weight loss and lung lesion damage in mice caused by influenza virus were improved by compound E-2o. Therefore, Alkoxy-substituted enamide E-2o could inhibit the replication of influenza viruses in vivo and in vitro, and has the potential to be developed into a drug for treating influenza.

Characterization of RNA driven structural changes in full length RIG-I leading to its agonism or antagonism

RIG-I (retinoic acid inducible gene-I) can sense subtle differences between endogenous and viral RNA in the cytoplasm, triggering an anti-viral immune response through induction of type I interferons (IFN) and other inflammatory mediators. Multiple crystal and cryo-EM structures of RIG-I suggested a mechanism in which the C-terminal domain (CTD) is responsible for the recognition of viral RNA with a 5'-triphoshate modification, while the CARD domains serve as a trigger for downstream signaling, leading to the induction of type I IFN. However, to date contradicting conclusions have been reached around the role of ATP in the mechanism of the CARD domains ejection from RIG-I's autoinhibited state. Here we present an application of NMR spectroscopy to investigate changes induced by the binding of 5'-triphosphate and 5'-OH dsRNA, both in the presence and absence of nucleotides, to full length RIG-I with all its methionine residues selectively labeled (Met-[ϵ-13CH3]). With this approach we were able to identify residues on the CTD, helicase domain, and CARDs that served as probes to sense RNA-induced conformational changes in those respective regions. Our results were analyzed in the context of either agonistic or antagonistic RNAs, by and large supporting a mechanism proposed by the Pyle Lab in which CARD release is primarily dependent on the RNA binding event.

Retinoic acid-inducible gene-I like receptor pathway in cancer: modification and treatment

Retinoic acid-inducible gene-I (RIG-I) like receptor (RLR) pathway is one of the most significant pathways supervising aberrant RNA in cells. In predominant conditions, the RLR pathway initiates anti-infection function via activating inflammatory effects, while recently it is discovered to be involved in cancer development as well, acting as a virus-mimicry responder. On one hand, the product IFNs induces tumor elimination. On the other hand, the NF-κB pathway is activated which may lead to tumor progression. Emerging evidence demonstrates that a wide range of modifications are involved in regulating RLR pathways in cancer, which either boost tumor suppression effect or prompt tumor development. This review summarized current epigenetic modulations including DNA methylation, histone modification, and ncRNA interference, as well as post-transcriptional modification like m6A and A-to-I editing of the upstream ligand dsRNA in cancer cells. The post-translational modulations like phosphorylation and ubiquitylation of the pathway's key components were also discussed. Ultimately, we provided an overview of the current therapeutic strategies targeting the RLR pathway in cancers.

Immune responses to Tilapia lake virus infection: what we know and what we don't know

Tilapia lake virus (TiLV) is a novel contagious pathogen associated with a lethal disease affecting and decimating tilapia populations on several continents across the globe. Fish viral diseases, such as Tilapia lake virus disease (TiLVD), represent a serious threat to tilapia aquaculture. Therefore, a better understanding of the innate immune responses involved in establishing an antiviral state can help shed light on TiLV disease pathogenesis. Moreover, understanding the adaptive immune mechanisms involved in mounting protection against TiLV could greatly assist in the development of vaccination strategies aimed at controlling TiLVD. This review summarizes the current state of knowledge on the immune responses following TiLV infection. After describing the main pathological findings associated with TiLVD, both the innate and adaptive immune responses and mechanisms to TiLV infection are discussed, in both disease infection models and in vitro studies. In addition, our work, highlights research questions, knowledge gaps and research areas in the immunology of TiLV infection where further studies are needed to better understand how disease protection against TiLV is established.

Multiple Porcine Innate Immune Signaling Pathways Are Involved in the Anti-PEDV Response

Porcine epidemic diarrhea virus (PEDV) has caused great damage to the global pig industry. Innate immunity plays a significant role in resisting viral infection; however, the exact role of innate immunity in the anti-PEDV response has not been fully elucidated. In this study, we observed that various porcine innate immune signaling adaptors are involved in anti-PEDV (AJ1102-like strain) activity in transfected Vero cells. Among these, TRIF and MAVS showed the strongest anti-PEDV activity. The endogenous TRIF, MAVS, and STING were selected for further examination of anti-PEDV activity. Agonist stimulation experiments showed that TRIF, MAVS, and STING signaling all have obvious anti-PEDV activity. The siRNA knockdown assay showed that TRIF, MAVS, and STING are also all involved in anti-PEDV response, and their remarkable effects on PEDV replication were confirmed in TRIF-/-, MAVS-/- and STING-/- Vero cells via the CRISPR approach. For further verification, the anti-PEDV activity of TRIF, MAVS, and STING could be reproduced in porcine IPEC-DQ cells treated with siRNAs. In summary, this study reveals that multiple pattern-recognition receptor (PRR) signaling pathways of porcine innate immunity play an important role in the anti-PEDV infection, providing new and useful antiviral knowledge for prevention and control of PEDV spreading.

An overview of anti-SARS-CoV-2 and anti-inflammatory potential of baicalein and its metabolite baicalin: Insights into molecular mechanisms

The current Coronavirus Disease 2019 (COVID-19) pandemic, caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), is highly contagious infection that breaks the healthcare systems of several countries worldwide. Till to date, no effective antiviral drugs against COVID-19 infection have reached the market, and some repurposed drugs and vaccines are prescribed for the treatment and prevention of this disease. The currently prescribed COVID-19 vaccines are less effective against the newly emergent variants of concern of SARS-CoV-2 due to several mutations in viral spike protein and obviously there is an urgency to develop new antiviral drugs against this disease. In this review article, we systematically discussed the anti-SARS-CoV-2 and anti-inflammatory efficacy of two flavonoids, baicalein and its 7-O-glucuronide, baicalin, isolated from Scutellaria baicalensis, Oroxylum indicum, and other plants as well as their pharmacokinetics and oral bioavailability, for development of safe and effective drugs for COVID-19 treatment. Both baicalein and baicalin target the activities of viral S-, 3CL-, PL-, RdRp- and nsp13-proteins, and host mitochondrial OXPHOS for suppression of viral infection. Moreover, these compounds prevent sepsis-related inflammation and organ injury by modulation of host innate immune responses. Several nanoformulated and inclusion complexes of baicalein and baicalin have been reported to increase oral bioavailability, but their safety and efficacy in SARS-CoV-2-infected transgenic animals are not yet evaluated. Future studies on these compounds are required for use in clinical trials of COVID-19 patients.

Advances in Radiotherapy Immune Modulation: From Bench-to-Bedside and Back Again

Pre-clinical and clinical data clearly demonstrate the immune modulatory effects of radiotherapy (RT) but clinical trials testing RT + immunotherapy have been equivocal. An improved understanding of the immune modulatory effects of RT and how practical parameters of RT delivery (site and number of lesions, dose, fractionation, timing) influence these effects are needed to optimally combine RT with immunotherapy. Additionally, increased exploration of immunotherapy combinations with RT, beyond immune checkpoint inhibitors, are needed. A "bench-to-bedside and back again" approach will improve our understanding of RT immune modulation and allow for the implementation of more effective RT + immunotherapy strategies.

Viral recognition and the antiviral interferon response

Interferons (IFNs) are antiviral cytokines that play a key role in the innate immune response to viral infections. In response to viral stimuli, cells produce and release interferons, which then act on neighboring cells to induce the transcription of hundreds of genes. Many of these gene products either combat the viral infection directly, e.g., by interfering with viral replication, or help shape the following immune response. Here, we review how viral recognition leads to the production of different types of IFNs and how this production differs in spatial and temporal manners. We then continue to describe how these IFNs play different roles in the ensuing immune response depending on when and where they are produced or act during an infection.

Crosstalk between TLR8 and RIG-I-like receptors enhances antiviral immune responses

Background

Toll-like receptor (TLR) agonists have been investigated due to their potential dual effects as latency reverting agents and immune modulatory compounds in people living with HIV (PLWH). Here, we investigated whether co-stimulation of TLR7/8 agonists with RIG-I-like receptor (RLR) agonists enhances antiviral immunity.

Methods

Peripheral blood mononuclear cells (PBMCs) and monocyte-derived dendritic cells (DCs) were incubated with TLR and RLR-agonists for 24 h and innate and adaptive immune responses were determined (maturation markers, cytokines in supernatant, ISG expression).

Results

Both TLR7 and TLR8 agonists induced pro-inflammatory cytokines in DCs as well as PBMCs. TLR8 agonists were more potent in inducing cytokine responses and had a stronger effect on DC-induced immunity. Notably, while all compounds induced IL-12p70, co-stimulation with TLR8 agonists and RLR agonist polyI: C induced significantly higher levels of IL-12p70 in PBMCs. Moreover, crosstalk between TLR8 and RLR agonists induced a strong type I Interferon (IFN) response as different antiviral IFN-stimulated genes were upregulated by the combination compared to the agonists alone.

Conclusion

Our data strongly suggest that TLR crosstalk with RLRs leads to strong antiviral immunity as shown by induction of IL-12 and type I IFN responses in contrast to TLRs alone. Thus, co-stimulation of TLRs and RLRs might be a powerful strategy to induce reactivation of latent reservoir as well as antiviral immunity that eliminates the reactivated cells.

Immunogenic Cell Death in Hematological Malignancy Therapy

Although the curative effect of hematological malignancies has been improved in recent years, relapse or drug resistance of hematological malignancies will eventually recur. Furthermore, the microenvironment disorder is an important mechanism in the pathogenesis of hematological malignancies. Immunogenic cell death (ICD) is a unique mechanism of regulated cell death (RCD) that triggers an intact antigen-specific adaptive immune response by firing a set of danger signals or damage-associated molecular patterns (DAMPs), which is an immunotherapeutic modality with the potential for the treatment of hematological malignancies. This review summarizes the existing knowledge about the induction of ICD in hematological malignancies and the current research on combining ICD inducers with other treatment strategies for hematological malignancies.

Enhanced immune complex formation in the lungs of patients with dermatomyositis

BACKGROUND

Interstitial lung disease is frequently comorbid with dermatomyositis and has a poor prognosis, especially in patients with the anti-melanoma differentiation-associated gene 5 (MDA5) autoantibody. However, the pathogenesis of dermatomyositis-related interstitial lung disease remains unclear.

METHODS

We examined 18 and 19 patients with dermatomyositis-related interstitial lung disease and idiopathic pulmonary fibrosis (control), respectively. Lung tissues obtained from these patients were semi-quantitatively evaluated by immunohistochemical staining with in-house anti-human MDA5 monoclonal antibodies, as well as anti-human immunoglobulin (Ig) G, IgM, IgA, and complement component 3(C3) antibodies. We established human MDA5 transgenic mice and treated them with rabbit anti-human MDA5 polyclonal antibodies, and evaluated lung injury and Ig and C3 expression.

RESULTS

MDA5 was moderately or strongly expressed in the lungs of patients in both groups, with no significant differences between the groups. However, patients with dermatomyositis-related interstitial lung disease showed significantly stronger expression of C3 (p < 0.001), IgG (p < 0.001), and IgM (p = 0.001) in the lungs than control. Moreover, lung C3, but IgG, IgA, nor IgM expression was significantly stronger in MDA5 autoantibody-positive dermatomyositis-related interstitial lung disease (n = 9) than in MDA5 autoantibody-negative dermatomyositis-related interstitial lung disease (n = 9; p = 0.022). Treatment with anti-MDA5 antibodies induced lung injury in MDA5 transgenic mice, and strong immunoglobulin and C3 expression was observed in the lungs of the mice.

CONCLUSION

Strong immunoglobulin and C3 expression in the lungs involve lung injury related to dermatomyositis-related interstitial lung disease. Enhanced immune complex formation in the lungs may contribute to the poor prognosis of MDA5 autoantibody-positive dermatomyositis-related interstitial lung disease.

The Roles of TRAF3 in Immune Responses

Seven tumor necrosis factor receptor- (TNFR-) associated factors (TRAFs) have been found in mammals, which are primarily involved in the signal translation of the TNFR superfamily, the Toll-like receptor (TLR) family, and the retinoic acid-inducible gene I- (RIG-I-) like receptor (RLR) family. TRAF3 is one of the most diverse members of the TRAF family. It can positively regulate type I interferon production while negatively regulating signaling pathways of classical nuclear factor-κB, nonclassical nuclear factor-κB, and mitogen-activated protein kinase (MAPK). This review summarizes the roles of TRAF3 signaling and the related immune receptors (e.g., TLRs) in several preclinical and clinical diseases and focuses on the roles of TRAF3 in immune responses, the regulatory mechanisms, and its role in disease.

Mint3 as a Potential Target for Cooling Down HIF-1α-Mediated Inflammation and Cancer Aggressiveness

Hypoxia-inducible factor-1α (HIF-1α) is a transcription factor that plays a crucial role in cells adapting to a low-oxygen environment by facilitating a switch from oxygen-dependent ATP production to glycolysis. Mediated by membrane type-1 matrix metalloproteinase (MT1-MMP) expression, Munc-18-1 interacting protein 3 (Mint3) binds to the factor inhibiting HIF-1 (FIH-1) and inhibits its suppressive effect, leading to HIF-1α activation. Defects in Mint3 generally lead to improved acute inflammation, which is regulated by HIF-1α and subsequent glycolysis, as well as the suppression of the proliferation and metastasis of cancer cells directly through its expression in cancer cells and indirectly through its expression in macrophages or fibroblasts associated with cancer. Mint3 in inflammatory monocytes enhances the chemotaxis into metastatic sites and the production of vascular endothelial growth factors, which leads to the expression of E-selectin at the metastatic sites and the extravasation of cancer cells. Fibroblasts express L1 cell adhesion molecules in a Mint3-dependent manner and enhance integrin-mediated cancer progression. In pancreatic cancer cells, Mint3 directly promotes cancer progression. Naphthofluorescein, a Mint3 inhibitor, can disrupt the interaction between FIH-1 and Mint3 and potently suppress Mint3-mediated inflammation, cancer progression, and metastasis without causing marked adverse effects. In this review, we will introduce the potential of Mint3 as a therapeutic target for inflammatory diseases and cancers.

Grouper cGAS is a negative regulator of STING-mediated interferon response

Cyclic GMP-AMP synthase (cGAS) is one of the classical pattern recognition receptors that recognizes mainly intracytoplasmic DNA. cGAS induces type I IFN responses to the cGAS-STING signaling pathway. To investigate the roles of cGAS-STING signaling pathway in grouper, a cGAS homolog (named EccGAS) was cloned and identified from orange-spotted grouper (Epinephelus coioides). The open reading frame (ORF) of EccGAS is 1695 bp, encodes 575 amino acids, and contains a Mab-21 typical structural domain. EccGAS is homologous to Sebastes umbrosus and humans at 71.8% and 41.49%, respectively. EccGAS mRNA is abundant in the blood, skin, and gills. It is uniformly distributed in the cytoplasm and colocalized in the endoplasmic reticulum and mitochondria. Silencing of EccGAS inhibited the replication of Singapore grouper iridovirus (SGIV) in grouper spleen (GS) cells and enhanced the expression of interferon-related factors. Furthermore, EccGAS inhibited EcSTING-mediated interferon response and interacted with EcSTING, EcTAK1, EcTBK1, and EcIRF3. These results suggest that EccGAS may be a negative regulator of the cGAS-STING signaling pathway of fish.

Transcriptome analysis of largemouth bass (Micropterus salmoides) challenged with LPS and polyI:C

Largemouth bass (Micropterus salmoides) is a worldwide commercially important aquatic species. In recent years, pathogenic diseases cause great economic losses and hinder the industry of largemouth bass. To further understand the immune response against pathogens in largemouth bass, splenic transcriptome libraries of largemouth bass were respectively constructed at 12 h post-challenged with phosphate-buffered saline (PBS), lipopolysaccharide (LPS) and polyinosinic-polycytidylic acid (polyI:C) by using RNA sequencing technology (RNA-seq). RNA libraries were constructed using 9 RNA splenic samples isolated from three biological replicates of the three groups and sequenced on the DNBSEQ platform. A total number of 86,306 unigenes were obtained. Through pairwise comparisons among the three groups, we identified 11,295 different expression genes (DEGs) exhibiting significant differences at the transcript level. There were 7, 7, and 13 signal pathways were significantly enriched in LPS-PBS comparison, polyI:C-PBS comparison, and LPS-polyI:C comparison, respectively, indicating that the immune response to different pathogens was distinct in largemouth bass. To the best of our knowledge, this is the first report on the immune response of largemouth bass against different pathogen-associated molecular patterns (PAMPs) stimuli using transcriptomic analysis. Our results provide a valuable resource and new insights to understanding the immune characteristics of largemouth bass against different pathogens.

DUOX2 regulates secreted factors in virus-infected respiratory epithelial cells that contribute to neutrophil attraction and activation

The first line of defense against respiratory viruses relies on the antiviral and proinflammatory cytokine response initiated in infected respiratory epithelial cells. The cytokine response not only restricts virus replication and spreading, but also orchestrates the subsequent immune response. The epithelial Dual Oxidase 2 (DUOX2) has recently emerged as a regulator of the interferon antiviral response. Here, we investigated the role of DUOX2 in the inflammatory cytokine response using a model of A549 cells deficient in DUOX2 generated using Crispr-Cas9 and infected by Sendai virus. We found that the absence of DUOX2 selectively reduced the induction of a restricted panel of 14 cytokines and chemokines secreted in response to Sendai virus by 20 to 89%. The secreted factors produced by epithelial cells upon virus infection promoted the migration, adhesion, and degranulation of primary human neutrophils, in part through the DUOX2-dependent secretion of TNF and chemokines. In contrast, DUOX2 expression did not impact neutrophil viability or NETosis, thereby highlighting a selective impact of DUOX2 in neutrophil functions. Overall, this study unveils previously unrecognized roles of epithelial DUOX2 in the epithelial-immune cells crosstalk during respiratory virus infection.

Type I interferon/STAT1 signaling regulates UBE2M-mediated antiviral innate immunity in a negative feedback manner

Type I interferon (IFN-I) signaling is central to inducing antiviral innate immunity. However, the mechanisms for IFN-I signaling self-regulation are still largely unknown. Here, we report that RNA virus-infected macrophages with UBE2M deficiency produced decreased IFN-I expression in a RIG-I-dependent manner, causing an aggravated viral infection. Mechanistically, UBE2M inhibits RIG-I degradation by preventing the interaction of RIG-I and E3 ligase STUB1, resulting in antiviral IFN-I signaling activation. Simultaneously, IFN-I signaling-activated STAT1 facilitates the transcription of Trim21, leading to increased UBE2M degradation and blunted antiviral immunity. Translationally, oral administration of milk-derived extracellular vesicles containing RING domain-truncated TRIM21 (TRIM21-ΔRING) lacking E3 ligase activity efficiently transfers TRIM21-ΔRING into macrophages. TRIM21-ΔRING suppresses UBE2M degradation by competitively binding to UBE2M with TRIM21, thereby enhancing antiviral immunity. Overall, we reveal a negative feedback loop of IFN-I signaling and develop a reagent to improve innate immunity against RNA viruses.