Porcine epidemic diarrhea virus inhibits dsRNA-induced interferon-β production in porcine intestinal epithelial cells by blockade of the RIG-I-mediated pathway

Developing Next-Generation Live Attenuated Vaccines for Porcine Epidemic Diarrhea Using Reverse Genetic Techniques

Porcine epidemic diarrhea virus (PEDV) is the etiology of porcine epidemic diarrhea (PED), a highly contagious digestive disease in pigs and especially in neonatal piglets, in which a mortality rate of up to 100% will be induced. Immunizing pregnant sows remains the most promising and effective strategy for protecting their neonatal offspring from PEDV. Although half a century has passed since its first report in Europe and several prophylactic vaccines (inactivated or live attenuated) have been developed, PED still poses a significant economic concern to the swine industry worldwide. Hence, there is an urgent need for novel vaccines in clinical practice, especially live attenuated vaccines (LAVs) that can induce a strong protective lactogenic immune response in pregnant sows. Reverse genetic techniques provide a robust tool for virological research from the function of viral proteins to the generation of rationally designed vaccines. In this review, after systematically summarizing the research progress on virulence-related viral proteins, we reviewed reverse genetics techniques for PEDV and their application in the development of PED LAVs. Then, we probed into the potential methods for generating safe, effective, and genetically stable PED LAV candidates, aiming to provide new ideas for the rational design of PED LAVs.

The death domain-associated protein suppresses porcine epidemic diarrhea virus replication by interacting with signal transducer and activator of transcription 1 and inducing downstream ISG15 expression

Porcine epidemic diarrhea virus (PEDV) is an enteric coronavirus that causes acute enteric disease in piglets and severely threatens the pig industry all over the world. Death domain-associated protein (DAXX) is a classical chaperone protein involved in multiple biological processes, such as cell apoptosis, transcriptional regulation, DNA damage repair, and host innate immunity. However, whether DAXX functions in the anti-PEDV innate immune responses remains unclear. In this study, we found that PEDV infection upregulated DAXX expression and induced its nucleocytoplasmic translocation in IPEC-J2 cells. Furthermore, we found that DAXX overexpression was inhibitory to PEDV replication, while downregulation of DAXX by RNA interference facilitated PEDV replication. The antiviral activity of DAXX was due to its positive effect on IFN-λ3-STAT1 signaling, as DAXX positively regulated STAT1 activation through their interaction in cytoplasm and enhancing the downstream ISG15 expression. Mutation of tryptophan at 621 to alanine in DAXX increased its abundance in the cytoplasm, leading to the upregulation of STAT1 phosphorylation and ISG15 expression. It indicated that cytoplasmic fraction of DAXX was advantageous for the STAT1-ISG15 signaling axis and PEDV inhibition. In summary, these results show that DAXX inhibits PEDV infection by increasing IFN-λ3-induced STAT1 phosphorylation and the downstream ISG15 expression.

Swine acute diarrhea syndrome coronavirus Nsp1 suppresses IFN-λ1 production by degrading IRF1 via ubiquitin-proteasome pathway

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is a novel porcine enteric coronavirus that causes acute watery diarrhea, vomiting, and dehydration in newborn piglets. The type III interferon (IFN-λ) response serves as the primary defense against viruses that replicate in intestinal epithelial cells. However, there is currently no information available on how SADS-CoV modulates the production of IFN-λ. In this study, we utilized IPI-FX cells (a cell line of porcine ileum epithelium) as an in vitro model to investigate the potential immune evasion strategies employed by SADS-CoV against the IFN-λ response. Our results showed that SADS-CoV infection suppressed the production of IFN-λ1 induced by poly(I:C). Through screening SADS-CoV-encoded proteins, nsp1, nsp5, nsp10, nsp12, nsp16, E, S1, and S2 were identified as antagonists of IFN-λ1 production. Specifically, SADS-CoV nsp1 impeded the activation of the IFN-λ1 promoter mediated by MAVS, TBK1, IKKε, and IRF1. Both SADS-CoV and nsp1 obstructed poly(I:C)-induced nuclear translocation of IRF1. Moreover, SADS-CoV nsp1 degraded IRF1 via the ubiquitin-mediated proteasome pathway without interacting with it. Overall, our study provides the first evidence that SADS-CoV inhibits the type III IFN response, shedding light on the molecular mechanisms employed by SADS-CoV to evade the host immune response.

A Comprehensive View on the Protein Functions of Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea (PED) virus (PEDV) is one of the main pathogens causing diarrhea in piglets and fattening pigs. The clinical signs of PED are vomiting, acute diarrhea, dehydration, and mortality resulting in significant economic losses and becoming a major challenge in the pig industry. PEDV possesses various crucial structural and functional proteins, which play important roles in viral structure, infection, replication, assembly, and release, as well as in escaping host innate immunity. Over the past few years, there has been progress in the study of PEDV pathogenesis, revealing the crucial role of the interaction between PEDV viral proteins and host cytokines in PEDV infection. At present, the main control measure against PEDV is vaccine immunization of sows, but the protective effect for emerging virus strains is still insufficient, and there is no ideal safe and efficient vaccine. Although scientists have persistently delved their research into the intricate structure and functionalities of the PEDV genome and viral proteins for years, the pathogenic mechanism of PEDV remains incompletely elucidated. Here, we focus on reviewing the research progress of PEDV structural and nonstructural proteins to facilitate the understanding of biological processes such as PEDV infection and pathogenesis.

Immune escape of bovine parvovirus by VP1 inhibiting IFN-β production through the RIG-I-like receptor pathway

OBJECTIVE

The present study aimed to explore if bovine parvovirus (BPV) impacts beta interferon (IFN-β) production and to reveal further molecular mechanism of BPV immune escape.

METHOD

The pCMV-Myc-BPV-VP1 recombinant plasmid was verified with both double-enzyme digestion and sequence. HEK 293 T cells were transfected with this recombinant protein and then infected with the vesicular stomatitis virus (VSV). Expression levels of IFN-β mRNA were detected using qPCR.

RESULTS

The expression level of BPV VP1 mRNA in the pCMV-Myc-BPV-VP1 group was significantly higher than those of the untreated group (UT) and pCMV-Myc vector group. BPV virus copies in bovine turbinate (BT) cells of the BPV-VP1 group were raised (P < 0.05) with an increment of 5.8 × 104. Expression levels of IFN-β mRNA of the BPV VP1 group in HEK 293 T cells were decreased (P < 0.01). Following treatment of TBK1 and IRF3(5D), IFN-β expression levels in HEK 293 T cells were depressed. Additionally, expression levels of TBK1, IRF3(5D), MDA5, and MAVS were less than those of the flag empty vector, respectively.

CONCLUSION

pCMV-Myc-BPV-VP1 could heighten transcription levels of VP1 protein in BT cells, promote BPV proliferation, and ascend the production of IFN-β. Overexpression of pCMV-Myc-BPV-VP decreased IFN-β mRNA expression in HEK 293 T cells and inhibited IFN-β production induced by TBK1 and IRF3(5D). Furthermore, BPV VP1 obviously declined expression levels of TBK1, IRF3(5D), MDA5, and MAVS in the RIG-I-like receptor (RLR) pathway. Our findings revealed a novel mechanism evolved by BPV VP1 to inhibit type I IFN production and provided a solid scientific basis into the immunosuppression of BPV.

Mechanism of Lactiplantibacillus plantarum regulating Ca2+ affecting the replication of PEDV in small intestinal epithelial cells

Porcine epidemic diarrhea virus (PEDV) mainly invades the small intestine and promotes an inflammatory response, eventually leading to severe diarrhea, vomiting, dehydration, and even death of piglets, which seriously threatens the economic development of pig farming. In recent years, researchers have found that probiotics can improve the intestinal microenvironment and reduce diarrhea. At the same time, certain probiotics have been shown to have antiviral effects; however, their mechanisms are different. Herein, we aimed to investigate the inhibitory effect of Lactiplantibacillus plantarum supernatant (LP-1S) on PEDV and its mechanism. We used IPEC-J2 cells as a model to assess the inhibitory effect of LP-1S on PEDV and to further investigate the relationship between LP-1S, Ca2+, and PEDV. The results showed that a divalent cation chelating agent (EGTA) and calcium channel inhibitors (Bepridil hydrochloride and BAPTA-acetoxymethylate) could inhibit PEDV proliferation while effectively reducing the intracellular Ca2+ concentration. Furthermore, LP-1S could reduce PEDV-induced loss of calcium channel proteins (TRPV6 and PMCA1b), alleviate intracellular Ca2+ accumulation caused by PEDV infection, and promote the balance of intra- and extracellular Ca2+ concentrations, thereby inhibiting PEDV proliferation. In summary, we found that LP-1S has potential therapeutic value against PEDV, which is realized by modulating Ca2+. This provides a potential new drug to treat PEDV infection.

Infectious bronchitis virus nucleocapsid protein suppressed type I interferon production by interfering with the binding of MDA5-dsRNA and interacting with LGP2

The type I interferon (IFN-I) is a critical component of the innate immune responses, and Coronaviruses (CoVs) from both the Alphacoronavirus and Betacoronavirus genera interfere with the IFN-I signaling pathway in various ways. Of the gammacoronaviruses that mainly infect birds, little is known about how infectious bronchitis virus (IBV), evades or interferes with the innate immune responses in avian hosts since few IBV strains have been adapted to grow in avian passage cells. Previously, we reported that a highly pathogenic IBV strain GD17/04 has adaptability in an avian cell line, providing a material basis for further study on the interaction mechanism. In the present work, we describe the suppression of IBV to IFN-I and the potential role of IBV-encoded nucleocapsid (N) protein. We show that IBV significantly inhibits the poly I: C-induced IFN-I production, accordingly the nuclear translocation of STAT1, and the expression of IFN-stimulated genes (ISGs). A detailed analysis revealed that N protein, acting as an IFN-I antagonist, significantly impedes the activation of the IFN-β promoter stimulated by MDA5 and LGP2 but does not counteract its activation by MAVS, TBK1, and IRF7. Further results showed that IBV N protein, verified to be an RNA-binding protein, interferes with MDA5 recognizing double-stranded RNA (dsRNA). Moreover, we found that the N protein targets LGP2, which is required in the chicken IFN-I signaling pathway. Taken together, this study provides a comprehensive analysis of the mechanism by which IBV evades avian innate immune responses.

Insights and progress on epidemic characteristics, genotyping, and preventive measures of PEDV in China: A review

Porcine Epidemic Diarrhoea (PED) is an acute, extremely infectious intestinal disease of pigs caused by the Porcine Epidemic Diarrhoea Virus (PEDV). The virus can affect pigs of all breeds and age groups and shows varying degrees of symptoms, with piglets, in particular, being infected with mortality rates of up to 100%. PEDV was first identified in China in the 1980s and in October 2010 a large-scale PED outbreak caused by a variant of PEDV occurred in China, resulting in huge economic losses. Initially, vaccination can effectively prevent the classical strain, but since December 2010, the PEDV variant has caused "persistent diarrhoea" with severe vomiting, watery diarrhoea, and high morbidity and mortality in newborn piglets as the dominant clinical features, with a significant increase in morbidity and mortality. This indicates that PEDV strains have mutated during evolution and that traditional vaccines no longer provide effective cross-immune protection, so it is necessary to optimize immunization programs and find effective treatments through epidemiological surveys of PEDV to reduce the economic losses caused by infections with mutated strains. This article reviews the progress of research on the aetiology, epidemiological characteristics, genotyping, pathogenesis, transmission routes, and comprehensive control of PEDV infection in China.

Porcine epidemic diarrhea virus (PEDV) ORF3 protein inhibits cellular type I interferon signaling through down-regulating proteins expression in RLRs-mediated pathway

Porcine epidemic diarrhea virus (PEDV) is an entero-pathogenic coronavirus, which belongs to the genus Alphacoronavirus in the family Coronaviridae, causing lethal watery diarrhea in piglets. Previous studies have shown that PEDV has developed an antagonistic mechanism by which it evades the antiviral activities of interferon (IFN), such as the sole accessory protein open reading frame 3 (ORF3) being found to inhibit IFN-β promoter activities, but how this mechanism used by PEDV ORF3 inhibits activation of the type I signaling pathway remains not fully understood. Thus, in this present study, we showed that PEDV ORF3 inhibited both polyinosine-polycytidylic acid (poly(I:C))- and IFNα2b-stimulated transcription of IFN-β and interferon-stimulated genes (ISGs) mRNAs. The expression levels of antiviral proteins in the retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs)-mediated pathway was down-regulated in cells with over-expression of PEDV ORF3 protein, but global protein translation remained unchanged and the association of ORF3 with RLRs-related antiviral proteins was not detected, implying that ORF3 only specifically suppressed the expression of these signaling molecules. At the same time, we also found that the PEDV ORF3 protein inhibited interferon regulatory factor 3 (IRF3) phosphorylation and poly(I:C)-induced nuclear translocation of IRF3, which further supported the evidence that type I IFN production was abrogated by PEDV ORF3 through interfering with RLRs signaling. Furthermore, PEDV ORF3 counteracted transcription of IFN-β and ISGs mRNAs, which were triggered by over-expression of signal proteins in the RLRs-mediated pathway. However, to our surprise, PEDV ORF3 initially induced, but subsequently reduced the transcription of IFN-β and ISGs mRNAs to normal levels. Additionally, mRNA transcriptional levels of signaling molecules located at IFN-β upstream were not inhibited, but elevated by PEDV ORF3 protein. Collectively, these results demonstrate that inhibition of type I interferon signaling by PEDV ORF3 can be realized through down-regulating the expression of signal molecules in the RLRs-mediated pathway, but not via inhibiting their mRNAs transcription. This study points to a new mechanism evolved by PEDV through blockage of the RLRs-mediated pathway by ORF3 protein to circumvent the host's antiviral immunity.

Heterogeneous Nuclear Protein U Degraded the m6A Methylated TRAF3 Transcript by YTHDF2 To Promote Porcine Epidemic Diarrhea Virus Replication

Porcine epidemic diarrhea virus (PEDV) belongs to the genus Alphacoronavirus of the Coronaviridae family and can cause fatal watery diarrhea in piglets, causing significant economic losses. Heterogeneous nuclear protein U (HNRNPU) is a novel RNA sensor involved in sensing viral RNA in the nucleus and mediating antiviral immunity. However, it remains elusive whether and how cytoplasmic PEDV can be sensed by the RNA sensor HNRNPU. In this study we determined that HNRNPU was the binding partner of Nsp13 by immunoprecipitation-liquid chromatography-tandem mass spectrometry (IP/LC-MS/MS) analysis. The interaction between Nsp13 and HNRNPU was demonstrated by using coimmunoprecipitation and confocal immunofluorescence. Next, we identified that HNRNPU expression is significantly increased during PEDV infection, whereas the transcription factor hepatocyte nuclear factor 1α (HNF1A) could negatively regulate HNRNPU expression. HNRNPU was retained in the cytoplasm by interaction with PEDV Nsp13. We found that HNRNPU overexpression effectively facilitated PEDV replication, while knockdown of HNRNPU impaired viral replication, suggesting a promoting function of HNRNPU to PEDV infection. Additionally, HNRNPU was found to promote PEDV replication by affecting TRAF3 degradation at the transcriptional level to inhibit PEDV-induced beta interferon (IFN-β) production. Mechanistically, HNRNPU downregulates TRAF3 mRNA levels via the METTL3-METTL14/YTHDF2 axis and regulates immune responses through YTHDF2-dependent mRNA decay. Together, our findings reveal that HNRNPU serves as a negative regulator of innate immunity by degrading TRAF3 mRNA in a YTHDF2-dependent manner and consequently facilitating PEDV propagation. Our findings provide new insights into the immune escape of PEDV. IMPORTANCE PEDV, a highly infectious enteric coronavirus, has spread rapidly worldwide and caused severe economic losses. During virus infection, the host regulates innate immunity to inhibit virus infection. However, PEDV has evolved a variety of different strategies to suppress host IFN-mediated antiviral responses. Here, we identified that HNRNPU interacted with viral protein Nsp13. HNRNPU protein expression was upregulated, and the transcription factor HNF1A could negatively regulate HNRNPU expression during PEDV infection. HNRNPU also downregulated TRAF3 mRNA through the METTL3-METTL14/YTHDF2 axis to inhibit the production of IFN-β and downstream antiviral genes in PEDV-infected cells, thereby promoting viral replication. Our findings reveal a new mechanism with which PEDV suppresses the host antiviral response.

Development of Specific Monoclonal Antibodies against Porcine RIG-I-like Receptors Revealed the Species Specificity

The RIG-I-like receptors (RLRs) play critical roles in sensing and combating viral infections, particularly RNA virus infections. However, there is a dearth of research on livestock RLRs due to a lack of specific antibodies. In this study, we purified porcine RLR proteins and developed monoclonal antibodies (mAbs) against porcine RLR members RIG-I, MDA5 and LGP2, for which one, one and two hybridomas were obtained, respectively. The porcine RIG-I and MDA5 mAbs each targeted the regions beyond the N-terminal CARDs domains, whereas the two LGP2 mAbs were both directed to the N-terminal helicase ATP binding domain in the Western blotting. In addition, all of the porcine RLR mAbs recognized the corresponding cytoplasmic RLR proteins in the immunofluorescence and immunochemistry assays. Importantly, both RIG-I and MDA5 mAbs are porcine specific, without demonstrating any cross-reactions with the human counterparts. As for the two LGP2 mAbs, one is porcine specific, whereas another one reacts with both porcine and human LGP2. Thus, our study not only provides useful tools for porcine RLR antiviral signaling research, but also reveals the porcine species specificity, giving significant insights into porcine innate immunity and immune biology.

Porcine Epidemic Diarrhea Virus nsp13 Protein Downregulates Neonatal Fc Receptor Expression by Causing Promoter Hypermethylation through the NF-κB Signaling Pathway

Porcine epidemic diarrhea virus (PEDV) is a highly pathogenic porcine enteric coronavirus that causes severe watery diarrhea and even death in piglets. The neonatal Fc receptor (FcRn) is the only transport receptor for IgG. FcRn expressed by intestinal epithelial cells can transport IgG from breast milk to piglets to provide immune protection. Previous studies have shown that viral infection affects FcRn expression. In this study, we showed for the first time, to our knowledge, that FcRn expression can be influenced by methyltransferases. In addition, we found that PEDV inhibited FcRn protein synthesis in porcine small intestinal epithelial cells postinfection. Then, we found that PEDV interfered with the transcription of genes through aberrant methylation modification of the FcRn promoter. DNA methyltransferase 3b (DNMT3b) has been implicated in this process. Using a series of PEDV structural and nonstructural protein (nsp) expression plasmids, we showed that nsp13 plays an important role in this aberrant methylation modification. PEDV nsp13 can affect the NF-κB canonical pathway and promote DNMT3b protein expression by facilitating p65 protein binding to chromatin. PEDV caused aberrant methylation of the FcRn promoter via DNMT3b. The same phenomenon was found in animal experiments with large white piglets. IgG transcytosis demonstrated that PEDV nsp13 can inhibit bidirectional IgG transport by FcRn. In addition, the core region of nsp13 (230-597 aa) is critical for FcRn inhibition. Taken together, to our knowledge, our findings revealed a novel immune escape mechanism of PEDV and shed new light on the design and development of vaccines and drugs.

Negative Regulation of RIG-I by Tim-3 Promotes H1N1 Infection

The mechanisms by which retinoic acid-inducible gene I (RIG-I), a critical RNA virus sensor, is regulated in many biological and pathological processes remain to be determined. Here, we demonstrate that T cell immunoglobulin and mucin protein-3 (Tim-3), an immune checkpoint inhibitor, mediates infection tolerance by suppressing RIG-I-type I interferon pathway. Overexpression or blockade of Tim-3 affects type I interferon expression, virus replication, and tissue damage in mice following H1N1 infection. Tim-3 signaling decreases RIG-I transcription via STAT1 in macrophages and promotes the proteasomal dependent degradation of RIG-I by enhancing K-48-linked ubiquitination via the E3 ligase RNF-122. Silencing RIG-I reversed Tim-3 blockage-mediated upregulation of type I interferon in macrophages. We thus identified a new mechanism through which Tim-3 mediates the immune evasion of H1N1, which may have clinical implications for the treatment of viral diseases.

miR-615 facilitates porcine epidemic diarrhea virus replication by targeting IRAK1 to inhibit type III interferon expression

Porcine epidemic diarrhea virus (PEDV) in the Coronavirus family is a highly contagious enteric pathogen in the swine industry, which has evolved mechanisms to evade host innate immune responses. The PEDV-mediated inhibition of interferons (IFNs) has been linked to the nuclear factor-kappa B (NF-κB) pathway. MicroRNAs (miRNAs) are involved in virus-host interactions and IFN-I regulation. However, the mechanism by which the PEDV regulates IFN during PEDV infection has not yet been investigated in its natural target cells. We here report a novel mechanism of viral immune escape involving miR-615, which was screened from a high-throughput sequencing library of porcine intestinal epithelial cells (IECs) infected with PEDV. PEDV infection altered the profiles of miRNAs and the activities of several pathways involved in innate immunity. Overexpression of miR-615 increased PEDV replication, inhibited IFN expression, downregulated the NF-κB pathway, and blocked p65 nuclear translocation. In contrast, knockdown of miR-615 enhanced IFN expression, suppressed PEDV replication, and activated the NF-κB pathway. We further determined that IRAK1 is the target gene of miR-615 in IECs. Our findings show that miR-615 suppresses activation of the NF-κB pathway by suppressing the IRAK1 protein and reducing the generation of IFN-IIIs, which in turn facilitates PEDV infection in IECs. Moreover, miR-615 inhibited PEDV replication and NF-κB pathway activation in both IECs and MARC-145 cells. These findings support an important role for miR-615 in the innate immune regulation of PEDV infections and provide a novel perspective for developing new treatments.

Co-infection of porcine deltacoronavirus and porcine epidemic diarrhea virus induces early TRAF6-mediated NF-κB and IRF7 signaling pathways through TLRs

Porcine deltacoronavirus (PDCoV) and porcine epidemic diarrhea virus (PEDV) infect the small intestine and cause swine enteric coronavirus disease. The mucosal innate immune system is the first line of defense against viral infection. The modulatory effect of PDCoV and PEDV coinfection on antiviral signaling cascades of the intestinal mucosa has not been reported. Here, we investigate the gene expression levels of pattern recognition receptors, downstream inflammatory signaling pathway molecules, and associated cytokines on the intestinal mucosa of neonatal piglets either infected with a single- or co-infected with PDCoV and PEDV using real-time PCR. The results demonstrate that single-PEDV regulates the noncanonical NF-κB signaling pathway through RIG-I regulation. In contrast, single-PDCoV and PDCoV/PEDV coinfection regulate proinflammatory and regulatory cytokines through TRAF6-mediated canonical NF-κB and IRF7 signaling pathways through TLRs. Although PDCoV/PEDV coinfection demonstrated an earlier modulatory effect in these signaling pathways, the regulation of proinflammatory and regulatory cytokines was observed simultaneously during single viral infection. These results suggested that PDCoV/PEDV coinfection may have synergistic effects that lead to enhanced viral evasion of the mucosal innate immune response.

Comparative transcriptomic analysis of porcine epidemic diarrhea virus epidemic and classical strains in IPEC-J2 cells

In recent years, porcine epidemic diarrhea (PED) has become widespread and caused huge economic losses for the global pig industry. There is growing evidence that frequent outbreaks of diarrhea are caused by the variants of porcine epidemic diarrhea virus (PEDV) with high pathogenicity. Herein, an epidemic strain of PEDV HLJ strain was isolated and characterized from Heilongjiang Province of China, and the whole genomic expression profile of intestinal porcine epithelial cells (IPEC-J2) infected with HLJ strain was investigated in comparison with classical CV777 strain. A total of 26,851 genes were identified, of these, 25,880 were known genes and 971 were novel genes. There were 258 differentially expressed genes (DEGs) identified between PEDV HLJ-infected and uninfected cells at 24 h post infection (hpi), and 201 DEGs between PEDV HLJ and CV777 infection. A comparative analysis revealed that 258 DEGs were enriched in 468 gene ontology (GO) terms and mapped to 179 KEGG pathways, and 201 DEGs in 1120 GO terms and mapped to 115 KEGG pathways for HLJ-infected cells in contrast to the uninfected and CV777-infected cells, respectively. Specifically, PEDV HLJ strain could activate anti-viral innate immune response and inflammation more intensively than CV777, in which mRNA levels of interferon (IFN-β), chemokines (CCL5 and CXCL10) and pro-inflammatory cytokines (IL-8 and TNF-α) were induced earlier and more strongly. Subsequently, 20 DEGs and 5 proteins were selected and validated by real-time fluorescence quantitative PCR (RT-qPCR) and western blot, and the results were consistent with the transcriptomic analysis. Overall, this study may be helpful for understanding the pathogenesis mechanism of PEDV variants, and contribute to the effective prevention and control of PEDV infection.

Porcine epidemic diarrhea virus strain FJzz1 infection induces type I/III IFNs production through RLRs and TLRs-mediated signaling

Interferons (IFNs) including type I/III IFNs are the major components of the host innate immune response against porcine epidemic diarrhea virus (PEDV) infection, and several viral proteins have been identified to antagonize type I/III IFNs productions through diverse strategies. However, the modulation of PEDV infection upon the activation of the host’s innate immune response has not been fully characterized. In this study, we observed that various IFN-stimulated genes (ISGs) were upregulated significantly in a time- and dose-dependent manner in LLC-PK1 cells infected with the PEDV G2 strain FJzz1. The transcriptions of IRF9 and STAT1 were increased markedly in the late stage of FJzz1 infection and the promotion of the phosphorylation and nuclear translocation of STAT1, implicating the activation of the JAK-STAT signaling pathway during FJzz1 infection. In addition, abundant type I/III IFNs were produced after FJzz1 infection. However, type I/III IFNs and ISGs decreased greatly in FJzz1-infected LLC-PK1 cells following the silencing of the RIG-I-like receptors (RLRs), including RIG-I and MDA5, and the Toll-like receptors (TLRs) adaptors, MyD88 and TRIF. Altogether, FJzz1 infection induces the production of type-I/III IFNs in LLC-PK1 cells, in which RLRs and TLRs signaling pathways are involved, followed by the activation of the JAK-STAT signaling cascade, triggering the production of numerous ISGs to exert antiviral effects of innate immunity.

Screening Host Antiviral Proteins under the Enhanced Immune Responses Induced by a Variant Strain of Porcine Epidemic Diarrhea Virus

While discussing the ideal candidates of viral restriction factor, the interferon (IFN) and interferon-stimulated genes (ISGs) could be considered potential targets. However, numerous viruses have evolved multiple strategies to modulate the host innate immune signaling for optimal infection, including the porcine epidemic diarrhea virus (PEDV), a coronavirus spreading widely around the world with high morbidity and mortality in piglets. The immunosuppression mediated by PEDV infection creates an impediment for studying the host-virus interactions and screening the antiviral ISGs. Here, the PEDV variant strain 85-7^C40 was screened using the continuous passaging, which showed significantly attenuated viral replication compared with its parent on MARC-145 cells. The comparative transcriptome analysis (accession nos. SRR13154018 to SRR13154026) indicated that 85-7^C40 infection led to enhanced immune response on MARC-145 cells, particularly to the IFN antiviral signaling, which mediated the stronger activation of numerous ISGs. Numerous ISGs activated by 85-7^C40 showed antiviral effects against the wild-type strain infection, particularly the IFI44 (an ISG upregulated specifically by the 85-7^C40 infection) and OASL (upregulated higher in 85-7^C40 than 85-7-infected cells), exhibited powerful antiviral activity. IFI44 promoted the production of RIG-I, while the OASL interacted directly with RIG-I, and then they both activated the phosphorylation of STAT1, indicating that they restricted PEDV replication by positively regulating the type I IFN response. Our results provided insight into the ISGs with antiviral activity against PEDV infection and also expanded our understanding of the innate immune response to PEDV infection, which may promote the development of novel therapeutics.

IMPORTANCE Host innate immune responses, particularly interferon (IFN) antiviral signaling, can activate diverse downstream ISGs to exert antiviral effects. However, porcine epidemic diarrhea virus (PEDV) infection has evolved multiple strategies to escape from this immune clearance. The immunosuppression mediated by PEDV infection creates an impediment for studying the host-virus interactions. We screened a PEDV variant strain, 85-7^C40, which induced enhanced immune responses on MARC-145 cells and thus mediated the stronger activation of numerous ISGs. The laboratory-generated variant might induce inconsistent immune responses with a natural wild-type strain during infection, while numerous ISGs activated by 85-7^C40 showed antiviral effects against the wild-type strain infection, particularly the IFI44 and OASL, restricted PEDV replication by positively regulating the type I IFN response. These findings were suggestive of the immune-enhanced variant being capable of using as an ideal viral model for screening the efficient antiviral proteins and elucidating the underlying mechanisms between PEDV and host innate immune responses.

The Interplay Between Coronavirus and Type I IFN Response

In the past few decades, newly evolved coronaviruses have posed a global threat to public health and animal breeding. To control and prevent the coronavirus-related diseases, understanding the interaction of the coronavirus and the host immune system is the top priority. Coronaviruses have evolved multiple mechanisms to evade or antagonize the host immune response to ensure their replication. As the first line and main component of innate immune response, type I IFN response is able to restrict virus in the initial infection stage; it is thus not surprising that the primary aim of the virus is to evade or antagonize the IFN response. Gaining a profound understanding of the interaction between coronaviruses and type I IFN response will shed light on vaccine development and therapeutics. In this review, we provide an update on the current knowledge on strategies employed by coronaviruses to evade type I IFN response.

Swine Enteric Coronaviruses (PEDV, TGEV, and PDCoV) Induce Divergent Interferon-Stimulated Gene Responses and Antigen Presentation in Porcine Intestinal Enteroids

Swine enteric coronaviruses (SECoVs) including porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), and porcine deltacoronavirus (PDCoV), account for the majority of lethal watery diarrhea in neonatal pigs and pose significant economic and public health burdens in the world. While the three SECoVs primarily infect intestinal epithelia in vivo and cause similar clinical signs, there are evident discrepancies in their cellular tropism and pathogenicity. However, the underlying mechanisms to cause the differences remain unclear. Herein, we employed porcine enteroids that are a physiologically relevant model of the intestine to assess the host epithelial responses following infection with the three SECoVs (PEDV, TGEV, and PDCoV). Although SECoVs replicated similarly in jejunal enteroids, a parallel comparison of transcriptomics datasets uncovered that PEDV and TGEV infection induced similar transcriptional profiles and exhibited a more pronounced response with more differentially expressed genes (DEGs) in jejunal enteroids compared with PDCoV infection. Notably, TGEV and PDCoV induced high levels of type I and III IFNs and IFN-stimulated gene (ISG) responses, while PEDV displayed a delayed peak and elicited a much lesser extent of IFN responses. Furthermore, TGEV and PDCoV instead of PEDV elicited a substantial upregulation of antigen-presentation genes and T cell-recruiting chemokines in enteroids. Mechanistically, we demonstrated that IFNs treatment markedly elevated the expression of NOD-like receptor (NLR) family NLRC5 and major histocompatibility complex class I (MHC-I) molecules. Together, our results indicate unique and common viral strategies for manipulating the global IFN responses and antigen presentation utilized by SECoVs, which help us a better understanding of host-SECoVs interactions.

Membrane proteomic analysis identifies the polarity protein PARD3 as a novel antiviral protein against PEDV infection

Porcine epidemic diarrhea virus (PEDV) is a highly pathogenic enteric coronavirus causing lethal watery diarrhea in suckling piglets. PEDV could remodel host membrane structures for their replication, assembly and escape from host cells. However, little is known about the host membrane proteins of PEDV infection. In this study, we analyzed differentially abundant proteins (DAPs) between PEDV infection group and control group and identified the polarity protein PARD3 as one of the most significantly DAPs. PARD3 is implicated in the formation of tight junctions at epithelial cell-cell contacts. Then, we found that PEDV infection promoted the degradation of PARD3 via the ubiquitin proteasome pathway. Moreover, knockdown of PARD3 promoted the proliferation of PEDV. Further study showed that the downregulation of PARD3 altered the normal morphology of the tight junction proteins and promoted apical and basolateral virus proliferation. Tight junctions enable epithelial cells to form physical barriers, which act as an innate immune mechanism that can impede viral infection and PEDV affected the barrier functions by causing degradation of PARD3. Taken together, this work is the first time to investigate the membrane protein profile of PEDV-infected cells using quantitative proteomics and suggests that PARD3 could be a potential novel antiviral protein against PEDV infection.

Significance

Membrane proteins are involved in various physiological and biochemical functions critical for cellular function. It is also dynamic in nature, where many proteins are changed during in response to environmental stress. However, membrane proteins are difficult to study because of their hydrophobicity. Membrane proteomic methods using mass spectrometry analysis have been developed and applied for the characterization of the plasma membrane and subcellular organelles of various virus infected cells. Porcine epidemic diarrhea virus (PEDV) is an enteric pathogen of importance to the swine industry, causing high mortality in neonatal piglets. Because PEDV infected Vero cells can lead to significant changes in cell membrane morphology and form syncytial lesions. Here, we isolated the membrane proteins of PEDV infected and control cells and applied isobaric tags for relative and absolute quantification (iTRAQ) labeling coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) to quantitatively identify the differentially abundant proteins (DAPs) in PEDV-infected Vero cells and confirmed the DAPs by performing RT-qPCR and Western blot analysis. Among these differential proteins, we focused on a down-regulated protein PARD3 which is important for cell tight junction and cell polarity. Loss of PARD3 can destroy the tight junction of cells and promote the proliferation of PEDV in the apical and basolateral sides. These findings will provide valuable information to better understand the mechanisms underlying the host defense responses to PEDV infection.

Porcine epidemic diarrhea virus nsp14 inhibits NF-κB pathway activation by targeting the IKK complex and p65

Coronaviruses (CoVs) are a group of related enveloped RNA viruses that have severe consequences in a wide variety of animals by causing respiratory, enteric or systemic diseases. Porcine epidemic diarrhea virus (PEDV) is an economically important CoV distributed worldwide that causes diarrhea in pigs. nsp14 is a nonstructural protein of PEDV that is involved in regulation of innate immunity and viral replication. However, the function and mechanism by which nsp14 modulates and manipulates host immune responses remain largely unknown. Here, we report that PEDV nsp14 is an NF-κB pathway antagonist. Overexpression PEDV nsp14 protein remarkably decreases SeV-, poly (I:C)- and TNF-α-induced NF-κB activation. Meanwhile, expression of proinflammatory cytokines is suppressed by nsp14. nsp14 inhibits the phosphorylation of IKKs by interacting with IKKs and p65. Furthermore, nsp14 suppresses TNF-α-induced phosphorylation and nuclear import of p65. Overexpression nsp14 considerably increases PEDV replication. These results suggest a novel mechanism employed by PEDV to suppress the host antiviral response, providing insights that can guide the development of antivirals against CoVs.

A Comparative Analysis of Coronavirus Nucleocapsid (N) Proteins Reveals the SADS-CoV N Protein Antagonizes IFN-β Production by Inducing Ubiquitination of RIG-I

Coronaviruses (CoVs) are a known global threat, and most recently the ongoing COVID-19 pandemic has claimed more than 2 million human lives. Delays and interference with IFN responses are closely associated with the severity of disease caused by CoV infection. As the most abundant viral protein in infected cells just after the entry step, the CoV nucleocapsid (N) protein likely plays a key role in IFN interruption. We have conducted a comprehensive comparative analysis and report herein that the N proteins of representative human and animal CoVs from four different genera [swine acute diarrhea syndrome CoV (SADS-CoV), porcine epidemic diarrhea virus (PEDV), severe acute respiratory syndrome CoV (SARS-CoV), SARS-CoV-2, Middle East respiratory syndrome CoV (MERS-CoV), infectious bronchitis virus (IBV) and porcine deltacoronavirus (PDCoV)] suppress IFN responses by multiple strategies. In particular, we found that the N protein of SADS-CoV interacted with RIG-I independent of its RNA binding activity, mediating K27-, K48- and K63-linked ubiquitination of RIG-I and its subsequent proteasome-dependent degradation, thus inhibiting the host IFN response. These data provide insight into the interaction between CoVs and host, and offer new clues for the development of therapies against these important viruses.

Porcine RIG-I and MDA5 Signaling CARD Domains Exert Similar Antiviral Function Against Different Viruses

The RIG-I-like receptors (RLRs) RIG-I and MDA5 play critical roles in sensing and fighting viral infections. Although RIG-I and MDA5 have similar molecular structures, these two receptors have distinct features during activation. Further, the signaling domains of the N terminal CARD domains (CARDs) in RIG-I and MDA5 share poor similarity. Therefore, we wonder whether the CARDs of RIG-I and MDA5 play similar roles in signaling and antiviral function. Here we expressed porcine RIG-I and MDA5 CARDs in 293T cells and porcine alveolar macrophages and found that MDA5 CARDs exhibit higher expression and stronger signaling activity than RIG-I CARDs. Nevertheless, both RIG-I and MDA5 CARDs exert comparable antiviral function against several viruses. Transcriptome analysis showed that MDA5 CARDs are more effective in regulating downstream genes. However, in the presence of virus, both RIG-I and MDA5 CARDs exhibit similar effects on downstream gene transcriptions, reflecting their antiviral function.

Identification of cellular proteins interacting with PEDV M protein through APEX2 labeling

Membrane (M) proteins of coronaviruses are the most abundant component of the virus envelope and play crucial roles in virus assembly, virus budding and the regulation of host immunity. To understand more about these functions in the context of PEDV M protein, forty host cell proteins interacting with the M protein were identified in the present study by exploiting the proximity-labeling enzyme APEX2 (a mutant soybean ascorbate peroxidase). Bioinformatic analysis showed that the identified host cell proteins were related to fifty-four signal pathways and a wide diversity of biological processes. Interaction between M and five of the identified proteins (RIG-I, PPID, NHE-RF1, S100A11, CLDN4) was confirmed by co-immunoprecipitation (Co-IP). In addition, knockdown of PPID and S100A11 genes by siRNA significantly improved virus production, indicating that the proteins encoded by the two genes were interfering with or down-regulating virus replication in infected cells. Identification of the host cell proteins accomplished in this study provides new information about the mechanisms underlying PEDV replication and immune evasion. SIGNIFICANCE: PEDV M protein is an essential structural protein implicated in viral infection, replication and assembly although the precise mechanisms underlying these functions remain enigmatic. In this study, we have identified 40 host cell proteins that interact with PEDV M protein using the proximity-labeling enzyme APEX2. Co-immunoprecipitation subsequently confirmed interactions between PEDV M protein and five host cell proteins, two of which (S100A11 and PPID) were involved in down-regulating virus replication in infected cells. This study is significant in that it formulates a strategy to provide new information about the mechanisms relating to the novel functions of PEDV M protein.

Analysis of Porcine RIG-I Like Receptors Revealed the Positive Regulation of RIG-I and MDA5 by LGP2

The RLRs play critical roles in sensing and fighting viral infections especially RNA virus infections. Despite the extensive studies on RLRs in humans and mice, there is a lack of systemic investigation of livestock animal RLRs. In this study, we characterized the porcine RLR members RIG-I, MDA5 and LGP2. Compared with their human counterparts, porcine RIG-I and MDA5 exhibited similar signaling activity to distinct dsRNA and viruses, via similar and cooperative recognitions. Porcine LGP2, without signaling activity, was found to positively regulate porcine RIG-I and MDA5 in transfected porcine alveolar macrophages (PAMs), gene knockout PAMs and PK-15 cells. Mechanistically, LGP2 interacts with RIG-I and MDA5 upon cell activation, and promotes the binding of dsRNA ligand by MDA5 as well as RIG-I. Accordingly, porcine LGP2 exerted broad antiviral functions. Intriguingly, we found that porcine LGP2 mutants with defects in ATPase and/or dsRNA binding present constitutive activity which are likely through RIG-I and MDA5. Our work provided significant insights into porcine innate immunity, species specificity and immune biology.

Porcine epidemic diarrhea virus E protein suppresses RIG-I signaling-mediated interferon-β production

Porcine epidemic diarrhea virus (PEDV) encodes many multifunctional proteins that inhibit host innate immune response during virus infection. As one of important structural proteins, PEDV E protein has been found to block the production of type I interferon (IFN) in virus life cycle, but little is known about this process that E protein subverts host innate immune. Thus, in this present study, we initiated the construction of eukaryotic expression vectors to express PEDV E protein. Subsequently, cellular localization analysis was performed and the results showed that the majority of PEDV E protein distributed at cytoplasm and localized in endoplasmic reticulum (ER). Over-expression of PEDV E protein significantly inhibited poly(I:C)-induced IFN-β and IFN-stimulated genes (ISGs) productions. We also found that PEDV E protein remarkably suppressed the protein expression of RIG-I signaling-associated molecules, but all their corresponding mRNA levels remained unaffected and unchanged. Furthermore, PEDV E protein obviously interfered with the translocation of IRF3 from cytoplasm to nucleus through direct interaction with IRF3, which is crucial for the IFN-β production induced by poly(I:C). Taken together, our results suggested that PEDV E protein acts as an IFN-β antagonist through suppression of the RIG-I-mediated signaling. This study will pave the way for the further investigation into the molecular mechanisms by which PEDV E protein evades host innate immune response.

Swine Acute Diarrhea Syndrome Coronavirus Nucleocapsid Protein Antagonizes Interferon-β Production via Blocking the Interaction Between TRAF3 and TBK1

Swine acute diarrhea syndrome coronavirus (SADS-CoV), first discovered in 2017, is a porcine enteric coronavirus that can cause acute diarrhea syndrome (SADS) in piglets. Here, we studied the role of SADS-CoV nucleocapsid (N) protein in innate immunity. Our results showed that SADS-CoV N protein could inhibit type I interferon (IFN) production mediated by Sendai virus (Sev) and could block the phosphorylation and nuclear translocation of interferon regulatory factor 3 (IRF3). Simultaneously, the IFN-β promoter activity mediated by TANK binding kinase 1 (TBK1) or its upstream molecules in the RLRs signal pathway was inhibited by SADS-CoV N protein. Further investigations revealed that SADS-CoV N protein could counteract interaction between TNF receptor-associated factor 3 (TRAF3) and TBK1, which led to reduced TBK1 activation and IFN-β production. Our study is the first report of the interaction between SADS-CoV N protein and the host antiviral innate immune responses, and the mechanism utilized by SADS-CoV N protein provides a new insight of coronaviruses evading host antiviral innate immunity.

Porcine haemagglutinating encephalomyelitis virus deactivates transcription factor IRF3 and limits type I interferon production

Porcine haemagglutinating encephalomyelitis virus (PHEV) is a member of coronavirus that causes acute infectious disease and high mortality in piglets. The transcription factor IRF3 is a central regulator of type I interferon (IFN) innate immune signalling. Here, we report that PHEV infection of RAW264.7 cells results in strong suppression of IFN-β production in the early stage. A comparative analysis of the upstream effector of IFN-β transcription demonstrated that deactivation of IRF3, but not p65 or ATF-2 proteins, is uniquely attributed to failure of early IFN-β induction. Moreover, the RIG-I/MDA5/MAVS/TBK1-dependent protective response that regulates the IRF3 pathway is not disrupted by PHEV and works well underlying the deactivated IRF3-mediated IFN-β inhibition. After challenge with poly(I:C), a synthetic analogue of dsRNA used to stimulate IFN-β secretion in the TLR-controlled pathway, we show that PHEV and poly(I:C) regulate IFN-β-induction via two different pathways. Collectively, our findings reveal that deactivation of IRF3 is a specific mechanism that contributes to termination of type I IFN signalling during early infection with PHEV independent of the conserved RIG-I/MAVS/MDA5/TBK1-mediated innate immune response.

The antiviral protein viperin interacts with the viral N protein to inhibit proliferation of porcine epidemic diarrhea virus

In the early stage of virus infection, the pattern recognition receptor (PRR) signaling pathway of the host cell is activated to induce interferon production, activating interferon-stimulated genes (ISGs) that encode antiviral proteins that exert antiviral effects. Viperin is one of the innate antiviral proteins that exert broad-spectrum antiviral effects by various mechanisms. Porcine epidemic diarrhea virus (PEDV) is a coronavirus that causes huge losses to the pig industry. Research on early antiviral responses in the gastrointestinal tract is essential for developing strategies to prevent the spread of PEDV. In this study, we investigated the mechanisms of viperin in PEDV-infected IPEJ-C2 cells. Increased expression of interferon and viperin and decreased replication of PEDV with a clear reduction in the viral load were observed in PEDV-infected IPEC-J2 cells. Amino acids 1-50 of porcine viperin contain an endoplasmic reticulum signal sequence that allows viperin to be anchored to the endoplasmic reticulum and are necessary for its function in inhibiting PEDV proliferation. The interaction of the viperin S-adenosylmethionine domain with the N protein of PEDV was confirmed via confocal laser scanning microscopy and co-immunoprecipitation. This interaction might interfere with viral replication or assembly to reduce virus proliferation. Our results highlight a potential mechanism whereby viperin is able to inhibit PEDV replication and play an antiviral role in innate immunity.

Porcine Epidemic Diarrhea Virus and the Host Innate Immune Response

Porcine epidemic diarrhea virus (PEDV), a swine enteropathogenic coronavirus (CoV), is the causative agent of porcine epidemic diarrhea (PED). PED causes lethal watery diarrhea in piglets, which has led to substantial economic losses in many countries and is a great threat to the global swine industry. Interferons (IFNs) are major cytokines involved in host innate immune defense, which induce the expression of a broad range of antiviral effectors that help host to control and antagonize viral infections. PEDV infection does not elicit a robust IFN response, and some of the mechanisms used by the virus to counteract the host innate immune response have been unraveled. PEDV evades the host innate immune response by two main strategies including: (1) encoding IFN antagonists to disrupt innate immune pathway, and (2) hiding its viral RNA to avoid the exposure of viral RNA to immune sensors. This review highlights the immune evasion mechanisms employed by PEDV, which provides insights for the better understanding of PEDV-host interactions and developing effective vaccines and antivirals against CoVs.

Successive Passage In Vitro Led to Lower Virulence and Higher Titer of A Variant Porcine Epidemic Diarrhea Virus

A highly virulent porcine epidemic diarrhea virus (PEDV) appeared in China and spread rapidly to neighbor countries, which have led to great economic losses to the pig industry. In the present study, we isolated a PEDV using Vero cells and serially propagated 100 passages. PEDV SDSX16 was characterized in vitro and in vivo. The viral titers increased to 107.6 TCID50/mL (100th) by serial passages. The spike (S) gene and the whole gene of the SDSX16 virus was fully sequenced to assess the genetic stability and relatedness to previously identified PEDV. Along with successive passage in vitro, there were 18 nucleotides (nt) deletion occurred in the spike (S) gene resulting in a deletion of six amino acids when the SDSX16 strain was passaged to the 64th generation, and this deletion was stable until the P100. However, the ORF1a/b, M, N, E, and ORF3 genes had only a few point mutations in amino acids and no deletions. According to growth kinetics experiments, the SDSX16 deletion strain significantly enhanced its replication in Vero cells since it was passaged to the 64th generation. The animal studies showed that PEDV SDSX16-P10 caused more severe diarrhea and vomiting, fecal shedding, and acute atrophic enteritis than SDSX16-P75, indicating that SDSX16-P10 is enteropathogenic in the natural host, and the pathogenicity of SDSX16 decreased with successive passage in vitro. However, SDSX16-P10 was found to cause lower levels of cytokine expression than SDSX16-P75 using real-time PCR and flow cytometry, such as IL1β, IL6, IFN-β, TNF-α, indicating that SDSX16-P10 might inhibit the expression of cytokines. Our data indicated that successive passage in vitro resulted in virulent attenuation in vivo of the PEDV variant strain SDSX16.

Expression Pattern Analysis of Antiviral Genes and Inflammatory Cytokines in PEDV-Infected Porcine Intestinal Epithelial Cells

Porcine diarrhea disease in newborn and suckling piglets due to infection with porcine epidemic diarrhea virus (PEDV) is a leading cause of economic loss in the pig industry globally. In this study, we investigated the molecular mechanism of the host innate immune response to PEDV infection. The expression dynamics of antiviral genes (e.g., RIG-1, PKR, OAS1, Mx1, and Mx2) and inflammatory cytokines (e.g., IFN-α, IFN-β, TNF-α, IL-6, IL-8, and IL-12) in porcine small intestinal epithelial (IPEC-J2) cells were analyzed following PEDV stimulation. The results showed that the expression of antiviral genes (e.g., PKR, OAS1, and Mx2) and inflammatory cytokines (e.g., IFN-α and TNF-α) were significantly reduced within 0–4 h post-infection (P < 0.05). However, all antiviral genes and inflammatory cytokines were up-regulated from 12 to 24 h (P < 0.05), and cytopathic changes were observed during this time. The expression of RIG-1, PKR, OAS1, Mx1, and Mx2 were significantly and positively correlated to each other during the entire infection (P < 0.01). The results suggested that the RIG-1, PKR, OAS1, Mx1, and Mx2 genes may play an important role in PEDV infection in piglets. Initially, PEDV displayed cellular invasion by inhibiting IFN-α transcription and interfering with the antiviral function of PKR, OAS1, and Mx2, ultimately induced an intense inflammatory response. The relationship between antiviral genes and inflammatory cytokines with PEDV infection at the cellular level provides a reference for studying the mechanism of resistance to PEDV infection in piglets.

Transmissible Gastroenteritis Virus Infection Up-Regulates FcRn Expression via Nucleocapsid Protein and Secretion of TGF-β in Porcine Intestinal Epithelial Cells

Transmissible gastroenteritis virus (TGEV) is a porcine intestinal coronavirus that causes fatal severe watery diarrhea in piglets. The neonatal Fc receptor (FcRn) is the only IgG transport receptor, its expression on mucosal surfaces is triggered upon viral stimulation, which significantly enhances mucosal immunity. We utilized TGEV as a model pathogen to explore the role of FcRn in resisting viral invasion in overall intestinal mucosal immunity. TGEV induced FcRn expression by activating NF-κB signaling in porcine small intestinal epithelial (IPEC-J2) cells, however, the underlying mechanisms are unclear. First, using small interfering RNAs, we found that TGEV up-regulated FcRn expression via TLR3, TLR9 and RIG-I. Moreover, TGEV induced IL-1β, IL-6, IL-8, TGF-β, and TNF-α production. TGF-β-stimulated IPEC-J2 cells highly up-regulated FcRn expression, while treatment with a JNK-specific inhibitor down-regulated the expression. TGEV nucleocapsid (N) protein also enhanced FcRn promoter activity via the NF-κB signaling pathway and its central region (aa 128–252) was essential for FcRn activation. Additionally, N protein-mediated FcRn up-regulation promotes IgG transcytosis. Thus, TGEV N protein and TGF-β up-regulated FcRn expression, further clarifying the molecular mechanism of up-regulation of FcRn expression by TGEV.

BST2 suppresses porcine epidemic diarrhea virus replication by targeting and degrading virus nucleocapsid protein with selective autophagy

Interferon-induced BST2 (bone marrow stromal cell antigen 2) inhibits viral replication by tethering enveloped virions to the cell surface to restrict viral release and by inducing the NFKB-dependent antiviral immune response. However, the mechanism by which BST2 uses the selective autophagy pathway to inhibit viral replication is poorly understood. In this study, we showed that BST2 expression was significantly increased during porcine epidemic diarrhea virus (PEDV) infection of Vero cells by IRF1 targeting its promoter. We also showed that BST2 suppressed PEDV replication by binding and degrading the PEDV-encoded nucleocapsid (N) protein. The downregulation of N protein was blocked by macroautophagy/autophagy inhibitors but not a proteasome inhibitor, implying that the N protein was degraded via the selective autophagy pathway. Both the BST2 and N protein interacted with the E3 ubiquitin ligase MARCHF8/MARCH8 and the cargo receptor CALCOCO2/NDP52, and the ubiquitination of N protein was necessary for the degradation of N mediated by the BST2-MARCHF8 axis. The knockdown of MARCHF8 or ATG5 with small interfering RNAs blocked the selective autophagy pathway, rescued the protein abundance of PEDV N in 293T cells, and prevented the inhibition of PEDV replication by BST2 in Vero cells. Together, our data demonstrate the novel mechanism of BST2-mediated virus restriction, in which BST2 recruits MARCHF8 to catalyze the ubiquitination of the PEDV N protein. The ubiquitinated N protein is then recognized by CALCOCO2/NDP52, which delivers it to autolysosome for degradation through the selective autophagy pathway. Abbreviations: 3MA: 3-methyladenine; ATG: autophagy-related; Baf A1: bafilomycin A₁; BST2: bone marrow stromal cell antigen 2; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CC: coiled-coil; ChIP: chromatin immunoprecipitation; Co-IP: co-immunoprecipitation; CQ: chloroquine; CT: cytoplasmic tail; DAPI: 4',6-diamidino-2-phenylindole; GPI: glycosyl-phosphatidylinositol; hpi: hours post infection; IRF1: interferon regulatory factor 1; ISG: IFN-stimulated gene; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MARCHF8/MARCH8: membrane-associated ring-CH-type finger 8; MOI: multiplicity of infection; N protein: nucleocapsid protein; PED: porcine epidemic diarrhea; PEDV: porcine epidemic diarrhea virus; RT: room temperature; siRNA: small interfering RNA; STAT: signal transducer and activator of transcription; TCID₅₀: 50% tissue culture infectious doses; TM: transmembrane.

Swine acute diarrhea syndrome coronavirus (SADS-CoV) antagonizes interferon-β production via blocking IPS-1 and RIG-I

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SADS-CoV failed to induce IFN-β expression and inhibited poly (I:C)-or SEV-mediated IFN-β production in IPEC-J2 cells.

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SADS-CoV interrupted poly (I:C)-induced phosphorylation and nuclear translocation of IRF3 and NF-κB.

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SADS-CoV failed to block IRF3, TBK1 and IKKε activity.

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SADS-CoV impeded IFN-β induction mediated by IPS-1 and RIG-I.

Swine acute diarrhea syndrome coronavirus (SADS-CoV), a newly emerging enteric coronavirus, is considered to be associated with swine acute diarrhea syndrome (SADS) which has caused significantly economic losses to the porcine industry. Interactions between SADS-CoV and the host innate immune response is unclear yet. In this study, we used IPEC-J2 cells as a model to explore potential evasion strategies employed by SADS-CoV. Our results showed that SADS-CoV infection failed to induce IFN-β production, and inhibited poly (I:C) and Sendai virus (SeV)-triggered IFN-β expression. SADS-CoV also blocked poly (I:C)-induced phosphorylation and nuclear translocation of IRF-3 and NF-κB. Furthermore, SADS-CoV did not interfere with the activity of IFN-β promoter stimulated by IRF3, TBK1 and IKKε, but counteracted its activation induced by IPS-1 and RIG-I. Collectively, this study is the first investigation that shows interactions between SADS-CoV and the host innate immunity, which provides information of the molecular mechanisms underlying SASD-CoV infection.

Manipulation of Intestinal Antiviral Innate Immunity and Immune Evasion Strategies of Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea virus (PEDV) infection causes watery diarrhea, dehydration, and high mortality in neonatal pigs, due to its clinical pathogenesis of the intestinal mucosal barrier dysfunction. The host's innate immune system is the first line of defence upon virus invasion of the small intestinal epithelial cells. In turn, the virus has evolved to modulate the host's innate immunity during infection, resulting in pathogen virulence, survival, and the establishment of successful infection. In this review, we gather current knowledge concerning the interplay between PEDV and components of host innate immunity, focusing on the role of cytokines and interferons in intestinal antiviral innate immunity, and the mechanisms underlying the immune evasion strategies of PEDV invasion. Finally, we provide some perspectives on the potential prevention and treatment for PEDV infection.

Isolation and Identification of Porcine Epidemic Diarrhea Virus and Its Effect on Host Natural Immune Response

Porcine epidemic diarrhea (PED) is a highly infectious intestinal disease caused by porcine epidemic diarrhea virus (PEDV). A PEDV strain was isolated from the piglet intestinal tract in Vero cells in Jiangsu Province, designated as the JS-A strain. PEDV was identified as the isolated virus by cytopathology, immunofluorescence assay, western blotting, transmission electron microscopy, and sequence analysis. The full-length genome of the JS-A isolate and the S gene were systematically analyzed, indicating that PEDV JS-A belongs to the G2a subtype, which is closely related to the prevalent PEDV in many countries and different from many current vaccines. Animal regression tests showed that piglets that are orally infected with the virus continue to develop diarrhea with yellowish and unpleasant odors. Further, piglets showed reduced food consumption and weight loss in the challenged group, while there were no abnormalities in the control group. In addition, Toll-like receptors (TLRs), RIG-I, and the downstream medium gene in the intestinal mucosa of newborn pigs infected with PEDV JS-A strain were studied. The neonatal Fc receptor (FcRn) was the only IgG transport receptor and protected IgG from degradation. Therefore, PEDV JS-A infection might inhibit FcRn expression by down-regulating TLRs and downstream signaling molecules. Taken together, isolation of the JS-A variant contributes to evolutionary analysis of the diarrhea virus. Further, the experimental infection model lays a foundation for further research related to vaccine development and the antiviral natural immune response of infected piglets, which helps us to better understand PEDV pathogenesis and immune mechanism.

Engineering a Live Attenuated Porcine Epidemic Diarrhea Virus Vaccine Candidate via Inactivation of the Viral 2'-O-Methyltransferase and the Endocytosis Signal of the Spike Protein

Porcine epidemic diarrhea virus (PEDV) causes high mortality in neonatal piglets; however, effective and safe vaccines are still not available. We hypothesized that inactivation of the 2'-O-methyltransferase (2'-O-MTase) activity of nsp16 and the endocytosis signal of the spike protein attenuates PEDV yet retains its immunogenicity in pigs. We generated a recombinant PEDV, KDKE4A, with quadruple alanine substitutions in the catalytic tetrad of the 2'-O-MTase using a virulent infectious cDNA clone, icPC22A, as the backbone. Next, we constructed another mutant, KDKE4A-SYA, by abolishing the endocytosis signal of the spike protein of KDKE4A Compared with icPC22A, the KDKE4A and KDKE4A-SYA mutants replicated less efficiently in vitro but induced stronger type I and type III interferon responses. The pathogenesis and immunogenicities of the mutants were evaluated in gnotobiotic piglets. The virulence of KDKE4A-SYA and KDKE4A was significantly reduced compared with that of icPC22A. Mortality rates were 100%, 17%, and 0% in the icPC22A-, KDKE4A-, and KDKE4A-SYA-inoculated groups, respectively. At 21 days postinoculation (dpi), all surviving pigs were challenged orally with a high dose of icPC22A. The KDKE4A-SYA- and KDKE4A-inoculated pigs were protected from the challenge, because no KDKE4A-SYA- and one KDKE4A-inoculated pig developed diarrhea whereas all the pigs in the mock-inoculated group had severe diarrhea, and 33% of them died. Furthermore, we serially passaged the KDKE4A-SYA mutant in pigs three times and did not find any reversion of the introduced mutations. The data suggest that KDKE4A-SYA may be a PEDV vaccine candidate.IMPORTANCE PEDV is the most economically important porcine enteric viral pathogen and has caused immense economic losses in the pork industries in many countries. Effective and safe vaccines are desperately required but still not available. 2'-O-MTase (nsp16) is highly conserved among coronaviruses (CoVs), and the inactivation of nsp16 in live attenuated vaccines has been attempted for several betacoronaviruses. We show that inactivation of both 2'-O-MTase and the endocytosis signal of the spike protein is an approach to designing a promising live attenuated vaccine for PEDV. The in vivo passaging data also validated the stability of the KDKE4A-SYA mutant. KDKE4A-SYA warrants further evaluation in sows and their piglets and may be used as a platform for further optimization. Our findings further confirmed that nsp16 can be a universal target for CoV vaccine development and will aid in the development of vaccines against other emerging CoVs.

Diversity, Cyanotoxin Production, and Bioactivities of Cyanobacteria Isolated from Freshwaters of Greece

Cyanobacteria are a diverse group of photosynthetic Gram-negative bacteria that produce an array of secondary compounds with selective bioactivity against a broad spectrum of organisms and cell lines. In this study, 29 strains isolated from freshwaters in Greece were classified using a polyphasic approach and assigned to Chroococcales, Synechococcales, and Nostocales, representing 11 genera and 17 taxa. There were good agreements between 16S ribosomal RNA (rRNA)-cpcBA-internal genetic spacer (IGS) characterization and morphological features, except for the Jaaginema-Limnothrix group which appears intermixed and needs further elucidation. Methanol extracts of the strains were analyzed for cyanotoxin production and tested against pathogenic bacteria species and several cancer cell lines. We report for the first time a Nostoc oryzae strain isolated from rice fields capable of producing microcystins (MCs) and a Chlorogloeopsis fritschii strain isolated from the plankton of a lake, suggesting that this species may also occur in freshwater temperate habitats. Strains with very high or identical 16S rRNA gene sequences displayed different antibacterial and cytotoxic activities. Extracts from Synechococcus cf. nidulans showed the most potent antibacterial activity against Staphylococcus aureus, whereas Jaaginema sp. strains exhibited potent cytotoxic activities against human colorectal adenocarcinoma and hepatocellular carcinoma cells. Jaaginema Thessaloniki Aristotle University Microalgae and Cyanobacteria (TAU-MAC) 0110 and 0210 strains caused pronounced changes in the actin network and triggered the formation of numerous lipid droplets in hepatocellular carcinoma and green monkey kidney cells, suggesting oxidative stress and/or mitochondrial damage leading to apoptosis.

PEDV nsp16 negatively regulates innate immunity to promote viral proliferation

Type-I IFNs (IFN-I) provide a key mediator of innate antiviral response during virus proliferation. Porcine epidemic diarrhea virus (PEDV), which causes diarrhea in swine of all ages, is a worldwide-distributed alphacoronavirus with economic importance. Here, we screened PEDV RNA modification enzymes involved in regulating antiviral response. Whereas the PEDV nsp13 barely regulates type I IFN, inflammatory cytokines (IL-6, TNF-a) and MHCII, nsp16 and nsp14 (to a lesser extent) down-regulate these antiviral effectors. Importantly, we found nsp16 KDKE tetrad appears to play a key role in interferon inhibition by mutating the D129 catalytic residue. Mechanistically, nsp16 down-regulates the activities of RIG-I and MDA5 mediated IFN-β and ISRE. In turn, the mRNA levels of IFIT family members (IFIT1, IFIT2, IFIT3) was inhibited in cells overexpressing nsp16. In addition, nsp10 enhanced the inhibitory effect of nsp16 on IFN-β. Altogether these results indicate PEDV nsp16 negatively regulates innate immunity to promote viral proliferation. Findings from this study provides novel perspective to advance the understanding in the pathogenesis of PEDV.

PEDV and PDCoV Pathogenesis: The Interplay Between Host Innate Immune Responses and Porcine Enteric Coronaviruses

Enteropathogenic porcine epidemic diarrhea virus (PEDV) and porcine deltacoronavirus (PDCoV), members of the coronavirus family, account for the majority of lethal watery diarrhea in neonatal pigs in the past decade. These two viruses pose significant economic and public health burdens, even as both continue to emerge and reemerge worldwide. The ability to evade, circumvent or subvert the host’s first line of defense, namely the innate immune system, is the key determinant for pathogen virulence, survival, and the establishment of successful infection. Unfortunately, we have only started to unravel the underlying viral mechanisms used to manipulate host innate immune responses. In this review, we gather current knowledge concerning the interplay between these viruses and components of host innate immunity, focusing on type I interferon induction and signaling in particular, and the mechanisms by which virus-encoded gene products antagonize and subvert host innate immune responses. Finally, we provide some perspectives on the advantages gained from a better understanding of host-pathogen interactions. This includes their implications for the future development of PEDV and PDCoV vaccines and how we can further our knowledge of the molecular mechanisms underlying virus pathogenesis, virulence, and host coevolution.

Interferon Regulatory Factor 3-Mediated Signaling Limits Middle-East Respiratory Syndrome (MERS) Coronavirus Propagation in Cells from an Insectivorous Bat

Insectivorous bats are speculated to be ancestral hosts of Middle-East respiratory syndrome (MERS) coronavirus (CoV). MERS-CoV causes disease in humans with thirty-five percent fatality, and has evolved proteins that counteract human antiviral responses. Since bats experimentally infected with MERS-CoV do not develop signs of disease, we tested the hypothesis that MERS-CoV would replicate less efficiently in bat cells than in human cells because of its inability to subvert antiviral responses in bat cells. We infected human and bat (Eptesicus fuscus) cells with MERS-CoV and observed that the virus grew to higher titers in human cells. MERS-CoV also effectively suppressed the antiviral interferon beta (IFNβ) response in human cells, unlike in bat cells. To determine if IRF3, a critical mediator of the interferon response, also regulated the response in bats, we examined the response of IRF3 to poly(I:C), a synthetic analogue of viral double-stranded RNA. We observed that bat IRF3 responded to poly(I:C) by nuclear translocation and post-translational modifications, hallmarks of IRF3 activation. Suppression of IRF3 by small-interfering RNA (siRNA) demonstrated that IRF3 was critical for poly(I:C) and MERS-CoV induced induction of IFNβ in bat cells. Our study demonstrates that innate antiviral signaling in E. fuscus bat cells is resistant to MERS-CoV-mediated subversion.

Bats and Coronaviruses

Bats are speculated to be reservoirs of several emerging viruses including coronaviruses (CoVs) that cause serious disease in humans and agricultural animals. These include CoVs that cause severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), porcine epidemic diarrhea (PED) and severe acute diarrhea syndrome (SADS). Bats that are naturally infected or experimentally infected do not demonstrate clinical signs of disease. These observations have allowed researchers to speculate that bats are the likely reservoirs or ancestral hosts for several CoVs. In this review, we follow the CoV outbreaks that are speculated to have originated in bats. We review studies that have allowed researchers to identify unique adaptation in bats that may allow them to harbor CoVs without severe disease. We speculate about future studies that are critical to identify how bats can harbor multiple strains of CoVs and factors that enable these viruses to “jump” from bats to other mammals. We hope that this review will enable readers to identify gaps in knowledge that currently exist and initiate a dialogue amongst bat researchers to share resources to overcome present limitations.

Nucleocapsid protein from porcine epidemic diarrhea virus isolates can antagonize interferon-λ production by blocking the nuclear factor-κB nuclear translocation

Porcine epidemic diarrhea virus (PEDV) is a highly infectious pathogen that can cause severe diseases in pigs and result in enormous economic losses in the worldwide swine industry. Previous studies revealed that PEDV exhibits an obvious capacity for modulating interferon (IFN) signaling or expression. The newly discovered type III IFN, which plays a crucial role in antiviral immunity, has strong antiviral activity against PEDV proliferation in IPEC-J2 cells. In this study, we aimed to investigate the effect of PEDV nucleocapsid (N) protein on type III IFN-λ. We found that the N proteins of ten PEDV strains isolated between 2013 and 2017 from different local farms shared high nucleotide identities, while the N protein of the CV777 vaccine strain formed a monophyletic branch in the phylogenetic tree. The N protein of the epidemic strain could antagonize type III IFN, but not type I or type II IFN expression induced by polyinosinic-polycytidylic acid (poly(I:C)) in IPEC-J2 cells. Subsequently, we demonstrated that the inhibition of poly(I:C)-induced IFN-λ3 production by PEDV N protein was dependent on the blocking of nuclear factor-κB (NF-κB) nuclear translocation. These findings might help increase understanding of the pathogenesis of PEDV and its mechanisms for evading the host immune response.

The nucleocapsid proteins of mouse hepatitis virus and severe acute respiratory syndrome coronavirus share the same IFN-β antagonizing mechanism: attenuation of PACT-mediated RIG-I/ MDA5 activation

Coronaviruses (CoVs) are a huge threat to both humans and animals and have evolved elaborate mechanisms to antagonize interferons (IFNs). Nucleocapsid (N) protein is the most abundant viral protein in CoV-infected cells, and has been identified as an innate immunity antagonist in several CoVs, including mouse hepatitis virus (MHV) and severe acute respiratory syndrome (SARS)-CoV. However, the underlying molecular mechanism(s) remain unclear. In this study, we found that MHV N protein inhibited Sendai virus and poly(I:C)-induced IFN-β production by targeting a molecule upstream of retinoic acid-induced gene I (RIG-I) and melanoma differentiation gene 5 (MDA5). Further studies showed that both MHV and SARS-CoV N proteins directly interacted with protein activator of protein kinase R (PACT), a cellular dsRNA-binding protein that can bind to RIG-I and MDA5 to activate IFN production. The N–PACT interaction sequestered the association of PACT and RIG-I/MDA5, which in turn inhibited IFN-β production. However, the N proteins from porcine epidemic diarrhea virus (PEDV) and porcine reproductive and respiratory syndrome virus (PRRSV), which are also classified in the order Nidovirales, did not interact and counteract with PACT. Taken together, our present study confirms that both MHV and SARS-CoV N proteins can perturb the function of cellular PACT to circumvent the innate antiviral response. However, this strategy does not appear to be used by all CoVs N proteins.

Differential gene modulation of pattern-recognition receptor TLR and RIG-I-like and downstream mediators on intestinal mucosa of pigs infected with PEDV non S-INDEL and PEDV S-INDEL strains

Porcine epidemic diarrhea virus (PEDV) strains can be divided into non-S-INDEL and S-INDEL strains. PEDV pathogenesis is strain-specific, and studies in neonatal pigs have demonstrated that the PEDV non-S-INDEL strains are more pathogenic than the PEDV S-INDEL strains. RNA viruses, including PEDV, can interact with a large number of pattern recognition receptors (PRRs) in the intestinal mucosa, including toll-like receptors (TLRs) and RIG-I-like receptors (RLRs). We investigated the differential gene modulation of TLRs, RIG-I, and downstream mediators on the intestinal mucosa of neonatal pigs infected with PEDV S-INDEL and non-S-INDEL strains. Ten five-day-old piglets were inoculated orally with 10 ml of 10⁴ TCDI₅₀/ml of either PEDV non-S-INDEL or S-INDEL strains. PEDV S-INDEL infection induced pro-inflammatory cytokines through the non-canonical NF-κB signaling pathway by activating RIG-I. In contrast, PEDV non-S-INDEL infection suppressed the induction of pro-inflammatory cytokines and type 1 interferon production by down-regulation of TLRs and downstream signaling molecules.

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Differential gene modulation of TLR and RIG-I-like receptors and downstream mediators.

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PEDV S-INDEL induces pro-inflammatory cytokines through non-canonical NF-κB signaling pathway.

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PEDV S-INDEL pro-inflammatory cytokines activation is RIG-I dependent.

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PEDV non-S-INDEL suppresses the induction of pro-inflammatory cytokines and type 1 interferon.

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PEDV non-S-INDEL effect is mediated by down-regulation of TLRs and its downstream-signaling molecules.

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PEDV S-INDEL and PEDV non-S-INDEL cause differential modulation on innate immune response pathways.

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Differential modulation could be translated into differences in pathogenesis and clinical outcomes.

Inhibition of NF-κB activity by the porcine epidemic diarrhea virus nonstructural protein 1 for innate immune evasion

Porcine epidemic diarrhea virus emerged in the US is known to suppress the type I interferons response during infection. In the present study using porcine epithelial cells, we showed that PEDV inhibited both NF-κB and proinflammatory cytokines. PEDV blocked the p65 activation in infected cells and suppressed the PRD II-mediated NF-κB activity. Of the total of 22 viral proteins, nine proteins were identified as NF-κB antagonists, and nsp1 was the most potent suppressor of proinflammatory cytokines. Nsp1 interfered the phosphorylation and degradation of IκBα, and thus blocked the p65 activation. Mutational studies demonstrated the essential requirements of the conserved residues of nsp1 for NF-κB suppression. Our study showed that PEDV inhibited NF-κB activity and nsp1 was a potent NF-κB antagonist for suppression of both IFN and early production of pro-inflammatory cytokines.

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PEDV inhibits type I IFNs and NF-κB-mediated pro-inflammatory cytokines.

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PEDV blocks p65 nuclear translocation in virus-infected cells.

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Among 22 viral proteins, nsp1, nsp3, nsp5, nsp7, nsp14, nsp15, nsp16, ORF3, and E are NF-κB antagonists.

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Nsp1 suppresses pro-inflammatory cytokines and p65 activation by blocking IκBα phosphorylation.

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The conserved residues of nsp1 are crucial for NF-κB suppression.

Transmissible gastroenteritis virus does not suppress IFN-β induction but is sensitive to IFN in IPEC-J2 cells

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TGEV infection would delay IFN-β production in IPEC-J2 cells.

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TGEV replication and IFN-β production have a similar trend in IPEC-J2 cells.

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The antiviral activity of IFN-I during TGEV infection is limited.

Coronaviruses tend to efficiently evade innate immune sensing. Alpha-coronaviruses interfere with the type I interferon (IFN) response in various ways, ensuring the limited activation of IFN responses. Transmissible gastroenteritis virus (TGEV), an Alphacoronavirus genera virus, is an important pathogen that mainly infects piglet, but little is known about the activation of the host immune response. We show that TGEV induces a delayed activation of the IFN response in intestinal epithelial cells. Briefly, IFN-β expression induced by TGEV infection is delayed with respect to that induced by poly(I:C) transfection. In addition, some of the IFN-stimulated genes (ISGs) were up-regulated in the early infection stage without obvious expression of IFN-β. Moreover, we show that activation of IFN responses induced by poly(I:C) could inhibit viral replication in the early infection stage, but failed in the late infection stage in IPEC-J2 cells. Finally, the activation of IFN responses induced by TGEV infection cannot inhibit viral replication. Taken together, this study provides a preliminary analysis of an interaction between TGEV and IFN-β responses of intestinal epithelial cells.