Pig BVDV-2 non-structural protein (Npro) links to cellular antiviral response in vitro

Current progress on innate immune evasion mediated by Npro protein of pestiviruses

Interferon (IFN), the most effective antiviral cytokine, is involved in innate and adaptive immune responses and is essential to the host defense against virus invasion. Once the host was infected by pathogens, the pathogen-associated molecular patterns (PAMPs) were recognized by the host pattern recognition receptors (PRRs), which activates interferon regulatory transcription factors (IRFs) and nuclear factor-kappa B (NF-κB) signal transduction pathway to induce IFN expression. Pathogens have acquired many strategies to escape the IFN-mediated antiviral immune response. Pestiviruses cause massive economic losses in the livestock industry worldwide every year. The immune escape strategies acquired by pestiviruses during evolution are among the major difficulties in its control. Previous experiments indicated that Erns, as an envelope glycoprotein unique to pestiviruses with RNase activity, could cleave viral ss- and dsRNAs, therefore inhibiting the host IFN production induced by viral ss- and dsRNAs. In contrast, Npro, the other envelope glycoprotein unique to pestiviruses, mainly stimulates the degradation of transcription factor IRF-3 to confront the IFN response. This review mainly summarized the current progress on mechanisms mediated by Npro of pestiviruses to antagonize IFN production.

Pestiviruses infection: Interferon-virus mutual regulation

Pestiviruses are a class of viruses that in some cases can cause persistent infection of the host, thus posing a threat to the livestock industry. Interferons (IFNs) are a group of secreted proteins that play a crucial role in antiviral defense. In this review, on the one hand, we elaborate on how pestiviruses are recognized by the host retinoic acid-inducible gene-I (RIG-I), melanoma-differentiation-associated protein 5 (MDA5), and Toll-like receptor 3 (TLR3) proteins to induce the synthesis of IFNs. On the other hand, we focus on reviewing how pestiviruses antagonize the production of IFNs utilizing various strategies mediated by self-encoded proteins, such as the structural envelope protein (E^rns) and non-structural protein (N^pro). Hence, the IFN signal transduction pathway induced by pestiviruses infection and the process of pestiviruses blockade on the production of IFNs intertwines into an intricate regulatory network. By reviewing the interaction between IFN and pestiviruses (based on studies on BVDV and CSFV), we expect to provide a theoretical basis and reference for a better understanding of the mechanisms of induction and evasion of the innate immune response during infection with these viruses.

75 years of bovine viral diarrhea virus: Current status and future applications of the use of directed antivirals

Bovine viral diarrhea virus (BVDV) was first reported 75 years ago and remains a source of major financial and production losses in the North American cattle industry. Currently, control methods in North America primarily center around biosecurity and vaccination programs; however, despite high levels of vaccination, the virus persists in the cattle herd due at least in part to the often-insidious nature of disease and the constant viremia and viral shedding of persistently infected animals which act as a reservoir for the virus. Continued development of targeted antivirals represents an additional tool for the prevention of BVDV-associated losses. Currently, in vivo studies of BVDV antivirals are relatively limited and have primarily been directed at the RNA-dependent RNA polymerase which represents the viral target with the highest potential for commercial development. Additional live animal studies have explored the potential of exogenous interferon treatment. Future research of commercial antivirals must focus on the establishment and validation of in vivo efficacy for compounds with demonstrated antiviral potential. The areas which provide the most viable economic justification for the research and development of antivirals drugs are the fed cattle sector, outbreak control, and wildlife or animals of high genetic value. With further development, targeted antivirals represent an additional tool for the management and control of BVDV in North American cattle herds.

Disruption of interferon-β production by the Npro of atypical porcine pestivirus

Atypical porcine pestivirus (APPV) is an emerging porcine virus that threatens global swine production. Pestiviruses can prevent interferon (IFN) production to avoid the host innate immune response, and the N^pro viral protein can play a critical role. Knowledge of the host immune response to APPV infection is limited. Here, we showed that the IFN-β production was suppressed by APPV-N^pro and the IFN regulatory factor 3 (IRF3) promoter activity stimulated by adaptor molecules of the IFN-β signaling pathway was also inhibited in the APPV-N^pro-expressed cells. The APPV-N^pro was able to interact with IRF3 and interfere the phosphorylation of IRF3, indicated that the IFN-β antagonism of APPV-N^pro mainly depended on blocking IRF3 activity. To identify the functional region of APPV-N^pro, a panel of truncated APPV-N^pro was constructed, and its influence on the IRF3 activation was investigated. The results showed that the N-terminal 31–51 amino acids of APPV-N^pro were mainly associated with inhibition of the IFN-β response. Taken together, this is the first study focusing on elucidating the function of APPV protein by revealing a novel mechanism of N^pro in disruption of host IFN-β production, which will enlighten future study in addressing APPV pathogenesis and immune evasion.

Transcriptional Profiling of Leucocyte Count Variation from Porcine Peripheral Blood Reveals Differential Gene Expression

Leucocytes have tremendous health-check importance related to the individual antiviral capacity of pigs and other mammals. However, the molecular mechanism of the immune response of blood leucocytes in pigs is not completely known. This study investigated the leucocyte-count variation before and after poly I:C stimulation in a Duroc–Erhualian F2 population. Pigs with increased and decreased differences in leucocyte counts were coded as increased responder (IR) and decreased responder (DR), respectively. Then, we used microarray technology to compare the gene-expression profiles of both groups of pigs. Transcriptomic analysis identified 129 differentially expressed genes (DEGs) in IR pigs and 136 DEGs in DR pigs. Forty-one common DEGs showed that both groups had similar expression patterns of immune responses. These results illustrated a differential expression in both groups. Furthermore, qPCR experiment was performed to verify the differential-expression profile. Functional annotation of the DEGs indicated that both IR and DR pigs were similar in several biological processes, including innate immune response, and also exhibited distinct differences in biological processes, molecular function, and pathways. These results provided insights into the mechanism underlying the antiviral capacity of pigs. Trial registration number is CAS Registry Number 24939-03-5.

Npro His49 and Erns Lys412 mutations in pig bovine viral diarrhea virus type 2 synergistically enhance the cellular antiviral response

Type I interferons are major components of the innate immune response of hosts, and accordingly, many viruses have evolved mechanisms to modulate the host response during infection. Bovine viral diarrhea virus (BVDV) nonstructural protein N^pro and structural protein E^rns play important roles in inhibiting type I interferon. The aim of this study was to explore the epistatic effects of amino acid mutations in N^pro and E^rns in porcine ST cells to characterize the immune response induced by BVDV-2. Plasmids with mutant amino acids His49 (H49), Glu22 (E22) in N^pro, and His300 (H300), Lys412 (K412) in E^rns which had been changed to Alanine (A) had similar effects on type I interferon production in MDBK and ST cells, but resulted in much greater ISG15, OAS, and Mx production in ST cells. The rescued vASH/N^proH49E^rnsK412 virus showed the best efficiency with respect to modulating antiviral cytokines, indicating that the amino acids N^pro H49 and E^rns K412 had highly synergistic effects in abolishing the ability to inhibit type I interferon. These findings have importance practical implications owing to the increasing prevalence of BVDV infections, including persistent infections, in domestic pigs.