No caspase activation but overexpression of Bcl-2 in bovine cells infected with noncytopathic bovine virus diarrhoea virus

Downregulation of the Long Noncoding RNA IALNCR Targeting MAPK8/JNK1 Promotes Apoptosis and Antagonizes Bovine Viral Diarrhea Virus Replication in Host Cells

Bovine viral diarrhea virus (BVDV) is the causative agent of the bovine viral diarrhea-mucosal disease, which is a leading cause of economic losses in the cattle industry worldwide. To date, many underlying mechanisms involved in BVDV-host interactions remain unclear, especially the functions of long noncoding RNAs (lncRNAs). In our previous study, the lncRNA expression profiles of BVDV-infected Madin-Darby bovine kidney (MDBK) cells were obtained by RNA-seq, and a significantly downregulated lncRNA IALNCR targeting MAPK8/JNK1 (a key regulatory factor of apoptosis) was identified through the lncRNA-mRNA coexpression network analysis. In this study, the function of IALNCR in regulating apoptosis to affect BVDV replication was further explored. Our results showed that BVDV infection-induced downregulation of the lncRNA IALNCR in the host cells could suppress the expression of MAPK8/JNK1 at both the mRNA and protein levels, thereby indirectly promoting the activation of caspase-3, leading to cell-autonomous apoptosis to antagonize BVDV replication. This was further confirmed by the small interfering RNA (siRNA)-mediated knockdown of the lncRNA IALNCR. However, the overexpression of the lncRNA IALNCR inhibited apoptosis and promoted BVDV replication. In conclusion, our findings demonstrated that the lncRNA IALNCR plays an important role in regulating host antiviral innate immunity against BVDV infection. IMPORTANCE Bovine viral diarrhea-mucosal disease caused by BVDV is an important viral disease in cattle, causing severe economic losses to the cattle industry worldwide. The molecular mechanisms of BVDV-host interactions are complex. To date, most studies focused only on how BVDV escapes host innate immunity. By contrast, how the host cell regulates anti-BVDV innate immune responses is rarely reported. In this study, a significantly downregulated lncRNA, with a potential function of inhibiting apoptosis (inhibiting apoptosis long noncoding RNA, IALNCR), was obtained from the lncRNA expression profiles of BVDV-infected cells and was experimentally evaluated for its function in regulating apoptosis and affecting BVDV replication. We demonstrated that downregulation of BVDV infection-induced lncRNA IALNCR displayed antiviral function by positively regulating the MAPK8/JNK1 pathway to promote cell apoptosis. Our data provided evidence that host lncRNAs regulate the innate immune response to BVDV infection.

Autophagy induced by bovine viral diarrhea virus infection counteracts apoptosis and innate immune activation

Bovine viral diarrhea virus (BVDV) is an important pathogen of cattle that plays a complex role in disease. There are two biotypes of BVDV: non-cytopathic (NCP) and cytopathic (CP). One strategy that has been used to treat or prevent virus-associated diseases is the modulation of autophagy, which is used by the innate immune system to defend against viral infection; however, at present, the interplay between autophagy and BVDV remains unclear. Madin-Darby bovine kidney cells stably expressing microtubule-associated protein 1 light chain 3B (LC3B) with green fluorescent protein (GFP) (GFP-LC3-MDBK cells) and autophagy-deficient MDBKs (shBCN1-MDBK cells) were constructed. Then MDBK, GFP-LC3-MDBK and shBCN1-MDBK cells were infected with CP or NCP BVDV strains. The LC3-II turnover rate was estimated by western blot, autophagosomes were visualized by confocal microscopy, and ultrastructural analysis was performed using electron microscopy. Autophagy flux was observed using chloroquine as an inhibitor of the autophagic process. The influence of autophagy on BVDV replication and release was investigated using virus titration, and its effect on cell viability was also studied. The effect of BVDV-induced autophagy on the survival of BVDV-infected host cell, cell apoptosis, and interferon (IFN) signalling was studied by flow cytometric analysis and quantitative RT-(q)PCR using shBCN1-MDBK cells. we found that infection with either CP or NCP BVDV strains induced steady-state autophagy in MDBK cells, as evident by the increased number of double- or single-membrane vesicles, the accumulation of GFP- microtubule-associated protein 1 light chain 3 (LC3) dots, and the conversion of LC3-I (cytosolic) to LC3-II (membrane-bound) forms. The complete autophagic process was verified by monitoring the LC3-II turnover ratio, lysosomal delivery, and proteolysis. In addition, we found that CP and NCP BVDV growth was inhibited in MDBK cells treated with high levels of an autophagy inducer or inhibitor, or in autophagy deficient-MDBK cells. Furthermore, our studies also suggested that CP and NCP BVDV infection in autophagy-knockdown MDBK cells increased apoptotic cell death and enhanced the expression of the mRNAs for IFN-α, Mx1, IFN-β, and OAS-1 as compared with control MDBK cells. Our study provides strong evidence that BVDV infection induces autophagy, which facilitates BVDV replication in MDBK cells and impairs the innate immune response. These findings might help to illustrate the pathogenesis of persistent infection caused by BVDV.

Bovine Viral Diarrhea Virus Infections

Bovine viral diarrhea virus (BVDV) continues to be of economic significance to the livestock industry in terms of acute disease and fetal loss. Many of the lesions relating to BVDV infection have been well described previously. The virus is perpetuated in herds through the presence of calves that are persistently infected. Relationships between various species and biotypes of BVDV and host defenses are increasingly understood. Understanding of the host defense mechanisms of innate immunity and adaptive immunity continues to improve, and the effects of the virus on these immune mechanisms are being used to explain how persistent infection develops. The noncytopathic biotype of BVDV plays the major role in its effects on the host defenses by inhibiting various aspects of the innate immune system and creation of immunotolerance in the fetus during early gestation. Recent advances have allowed for development of affordable test strategies to identify and remove persistently infected animals. With these improved tests and removal strategies, the livestock industry can begin more widespread effective control programs.

Apoptosis in Bovine viral diarrhea virus (BVDV)-induced mucosal disease lesions: a histological, immunohistological, and virological investigation

Cattle persistently infected with a noncytopathic Bovine viral diarrhea virus (BVDV) are at risk of developing fatal "mucosal disease" (MD). The authors investigated the role of various apoptosis pathways in the pathogenesis of lesions in animals suffering from MD. Therefore, they compared the expression of caspase-3, caspase-8, caspase-9, and Bcl-2L1 (Bcl-x) in tissues of 6 BVDV-free control animals, 7 persistently infected (PI) animals that showed no signs of MD (non-MD PI animals), and 11 animals with MD and correlated the staining with the localization of mucosal lesions. Caspase-3 and -9 staining were markedly stronger in MD cases and were associated with mucosal lesions, even though non-MD PI animals and negative controls also expressed caspase-9. Conversely, caspase-8 was not elevated in any of the animals analyzed. Interestingly, Bcl-x also colocalized with mucosal lesions in the MD cases. However, Bcl-x was similarly expressed in tissues from all 3 groups, and thus, its role in apoptosis needs to be clarified. This study clearly illustrates ex vivo that the activation of the intrinsic, but not the extrinsic, apoptosis pathway is a key element in the pathogenesis of MD lesions observed in cattle persistently infected with BVDV. However, whether direct induction of apoptosis in infected cells or indirect effects induced by the virus are responsible for the lesions observed remains to be established.

Characterization of apoptosis pathways (intrinsic and extrinsic) in lymphoid tissues of calves inoculated with non-cytopathic bovine viral diarrhoea virus genotype-1

Previous studies have shown that activation of effector caspase-3 is associated with the apoptosis of lymphocytes occurring during infection with bovine viral diarrhoea virus (BVDV); however, the regulation of the apoptosis pathways that induce cell death via activation of effector caspase-3 has not yet been clarified. The aim of this study was to examine immunohistochemically the expression of cleaved caspase (CCasp)-8 (initiator caspase of the extrinsic pathway), CCasp9 (initiator caspase of the intrinsic pathway) and Bcl-2 (an anti-apoptotic marker) in gut-associated lymphoid tissue (GALT) of the ileum from calves inoculated with a non-cytopathic strain of BVDV genotype-1. CCasp8 had similar expression to that of CCasp3. In interfollicular T-cell areas there was moderate apoptosis and evidence of moderate activation of initiator caspase-8. In B-cell follicles there was marked lymphocyte apoptosis and evidence of intense caspase-8 activation, highlighting the potentially major role of the extrinsic pathway in lymphocyte apoptosis in the GALT during BVDV infection. Additionally, there was a significant decrease in the number of CCasp9(+) cells from the start of the experiment and this was linked to inactivation of caspase-9. Therefore, the intrinsic pathway may play only a minor role in the induction of lymphocyte apoptosis. Finally, the observed overexpression of Bcl-2 protein could play a major role in protecting lymphocytes in the T-cell areas against apoptosis, while low levels of Bcl-2 expression could be associated with the follicular lymphocyte apoptosis occurring during BVDV infection.

Neuropathologic Study of Border Disease Virus in Naturally Infected Fetal and Neonatal Small Ruminants and Its Association With Apoptosis

The present study describes the pathologic changes and cellular apoptosis in the central nervous system (CNS) of fetal and neonatal small ruminants infected with border disease virus (BDV), as demonstrated by immunohistochemistry and in situ hybridization. Abortions of ewes and goats were observed, as were births of lambs and kids with poor survival rates and nervous signs. Lesions included cerebellar hypoplasia, porencephaly, hydranencephaly, and nonsuppurative meningoencephalomyelitis with hypomyelinogenesis. Viral antigens and RNA were present in neuropil, glial, and neuronal cells, especially in periventricular areas, cerebellum, and brainstem. TUNEL positivity and labeling of anti-bax and anti-caspases 3, 8, and 9 were detected in BDV-infected CNSs, especially in glial and neuronal cells. The double immunostaining and TUNEL assay revealed that in BDV-infected animals, not only were BDV-infected glial and neuronal cells undergoing apoptosis, but so were uninfected cells in close vicinity of BDV-infected cells. The expression of activated caspases 3, 8, 9; bax; and TUNEL in glial and neuronal cells of the infected fetal and neonatal kids were significantly ( P < .05) higher than those of the infected fetal and neonatal lambs. Yet, the expression of bcl-2 in the CNSs of the infected fetal and neonatal lambs was higher ( P < .05) in neuronal and glial cells than in those of the infected fetal and neonatal kids. The results suggest that cell death in the BDV-infected CNS is induced by intrinsic and extrinsic cascades of apoptotic pathways.

Bovine viral diarrhea virus NS4B protein is an integral membrane protein associated with Golgi markers and rearranged host membranes

Background

Very little is known about BVDV NS4B, a protein of approximately 38 kDa. However, a missense mutation in NS4B has been implicated in changing BVDV from a cytopathic to noncytopathic virus, suggesting that NS4B might play a role in BVDV pathogenesis. Though this is one possible function, it is also likely that NS4B plays a role in BVDV genome replication. For example, BVDV NS4B interacts with NS3 and NS5A, implying that NS4B is part of a complex, which contains BVDV replicase proteins. Other possible BVDV NS4B functions can be inferred by analogy to hepatitis C virus (HCV) NS4B protein. For instance, HCV NS4B remodels host membranes to form the so-called membranous web, the site for HCV genome replication. Finally, HCV NS4B is membrane-associated, implying that HCV NS4B may anchor the virus replication complex to the membranous web structure. Unlike its HCV counterpart, we know little about the subcellular distribution of BVDV NS4B protein. Further, it is not clear whether NS4B is localized to host membrane alterations associated with BVDV infection.

Results

We show first that release of infectious BVDV correlates with the kinetics of BVDV genome replication in infected cells. Secondly, we found that NS4B subcellular distribution changes over the course of BVDV infection. Further, BVDV NS4B is an integral membrane protein, which colocalizes mainly with the Golgi compartment when expressed alone or in the context of BVDV infection. Additionally, BVDV induces host membrane rearrangement and these membranes contain BVDV NS4B protein. Finally, NS4B colocalizes with replicase proteins NS5A and NS5B proteins, raising the possibility that NS4B is a component of the BVDV replication complex. Interestingly, NS4B was found to colocalize with mitochondria suggesting that this organelle might play a role in BVDV genome replication or cytopathogenicity.

Conclusion

These results show that BVDV NS4B is an integral membrane protein associated with the Golgi apparatus and virus-induced membranes, the putative site for BVDV genome replication. On the basis of NS4B Colocalization with NS5A and NS5B, we conclude that NS4B protein is an integral component of the BVDV replication complex.

Apoptosis in lymphoid tissues of calves inoculated with non-cytopathic bovine viral diarrhea virus genotype 1: activation of effector caspase-3 and role of macrophages

The mechanisms responsible for lymphocyte apoptosis in bovine viral diarrhoea have not yet been clarified. Previous work suggests that bovine viral diarrhea virus (BVDV) is only directly responsible for the destruction of a small number of lymphocytes. The aim of this study was to clarify, in vivo, the role of macrophages in lymphocyte destruction through indirect mechanisms linked to the biosynthetic activation of these immunocompetent cells on ileal Peyer's patches, as well as the distribution and quantification of apoptosis. Eight colostrum-deprived calves were inoculated intranasally with a non-cytopathic strain of BVDV genotype 1 and killed in batches of two at 3, 6, 9 and 14 days post-inoculation (p.i.). The progressive depletion of Peyer's patches was found to be due to massive lymphocyte apoptosis, with an increase in cleaved caspase-3 and TUNEL-positive cells. Lymphoid depletion was accompanied, from 3 days p.i., by a significant rise in macrophage numbers both in lymphoid follicles and in interfollicular areas. Some macrophages showed signs of viral infection, together with subcellular changes indicative of phagocyte activation and, in some cases, of secretory activity. However, the number of macrophages that showed positive immunostaining for tumour necrosis factor-α and interleukin-1α, cytokines with a proven ability to induce apoptosis, remained low throughout the experiment in lymphoid follicles, where most apoptotic cells were found. These results thus appear to rule out a major involvement of macrophages and macrophage-secreted chemical mediators in the apoptosis of follicular B lymphocytes during BVDV infection.

Expression of the NS3 protease of cytopathogenic bovine viral diarrhea virus results in the induction of apoptosis but does not block activation of the beta interferon promoter

Bovine viral diarrhea virus (BVDV; genus Pestivirus) can exist as two biotypes, cytopathogenic (CP) and non-cytopathogenic (NCP). The CP form differs from NCP by the continual expression of free non-structural protein 3 (NS3). CP BVDV infection of cultured cells induces apoptosis, whereas NCP BVDV infection has been reported to block the induction of beta interferon (IFN-beta). To investigate the viral mechanisms underlying these effects, NS3 or NS2-3 proteins of NCP and CP BVDV biotypes, together with the cognate NS3 co-factor NS4A, were expressed in cells, and their effect on apoptosis and induction of IFN-beta was investigated. Expression of NS3/4A resulted in increased activity of caspase-9 and caspase-3, indicating induction of the intrinsic apoptosis pathway. Mutational analysis revealed that a protease-inactive NS3/4A was unable to induce apoptosis, suggesting that NS3 protease activity is required for initiation of apoptosis during CP BVDV infection. The ability of NS2-3 to modulate activation of the IFN-beta promoter was also investigated. These studies confirmed that, unlike the related hepatitis C virus and GB virus-B, BVDV proteases are unable to inhibit TLR3- and RIG-I-dependent activation of the IFN-beta promoter. These data suggest that BVDV NS3/4A is responsible for regulating the levels of cellular apoptosis and provide new insights regarding the viral elements associated with CP biotype pathogenesis.

Activation and modulation of antiviral and apoptotic genes in pigs infected with classical swine fever viruses of high, moderate or low virulence

The immune response to CSFV and the strategies of this virus to evade and suppress the pigs’ immune system are still poorly understood. Therefore, we investigated the transcriptional response in the tonsils, median retropharyngeal lymph node (MRLN), and spleen of pigs infected with CSFV strains of similar origin with high, moderate, and low virulence. Using a porcine spleen/intestinal cDNA microarray, expression levels in RNA pools prepared from infected tissue at 3 dpi (three pigs per virus strain) were compared to levels in pools prepared from uninfected homologue tissues (nine pigs). A total of 44 genes were found to be differentially expressed. The genes were functionally clustered in six groups: innate and adaptive immune response, interferon-regulated genes, apoptosis, ubiquitin-mediated proteolysis, oxidative phosphorylation and cytoskeleton. Significant up-regulation of three IFN-γ-induced genes in the MRLNs of pigs infected with the low virulence strain was the only clear qualitative difference in gene expression observed between the strains with high, moderate and low virulence. Real-time PCR analysis of four response genes in all individual samples largely confirmed the microarray data at 3 dpi. Additional PCR analysis of infected tonsil, MRLN, and spleen samples collected at 7 and 10 dpi indicated that the strong induction of expression of the antiviral response genes chemokine CXCL10 and 2′–5′ oligoadenylate synthetase 2, and of the TNF-related apoptosis-inducing ligand (TRAIL) gene at 3 dpi, decreased to lower levels at 7 and 10 dpi. For the highly and moderately virulent strains, this decrease in antiviral and apoptotic gene expression coincided with higher levels of virus in these immune tissues.

Increase in proto-oncogene mRNA transcript levels in bovine lymphoid cells infected with a cytopathic type 2 bovine viral diarrhea virus

Infection of susceptible animals with bovine viral diarrhea viruses (BVDV) can result in an array of disease symptoms that are dependent in part on the strain of infecting virus and the physiological status of the host. BVDV are lymphotrophic and exist as two biotypes. Cytopathic BVDV kill cells outright while noncytopathic strains can readily establish persistent infections. The molecular mechanisms behind these different affects are unknown. To gain a better understanding of the mechanisms of disease, serial analysis of gene expression (SAGE), a powerful method for global gene expression analysis, was employed to examine gene expression changes in BVDV-infected BL3 cells, a bovine B-cell lymphosarcoma cell line. SAGE libraries were constructed from mRNA derived from BL3 cells that were noninfected or infected with the cytopathic BVDV2 strain 296c. Annotation of the SAGE data showed the expression of many genes that are characteristic of B cells and integral to their function. Comparison of the SAGE databases also revealed a number of genes that were differentially expressed. Of particular interest was the increased numbers of transcripts encoding proto-oncogenes (c-fos, c-jun, junB, junD) in 296c-infected cells, all of which are constituents of the AP-1 transcriptional activation complex. Real-time RT-PCR confirmed these results and indicated that the actual increases were larger than that predicted by SAGE. In contrast, there was no corresponding increase in protein levels, but instead a significant decrease of c-jun and junB protein levels in the infected BL3 cells was observed. Rather than an increase in transcription of these genes, it appeared that these proto-oncogenes transcripts accumulated in the BVDV2-infected cells.

Cytoplasmic vacuolization responses to cytopathic bovine viral diarrhoea virus

Bovine Viral Diarrhea Virus (BVDV) is a positive sense, single-stranded RNA virus which exhibits two biotypes in standard cell culture systems. The cytopathic strains of this virus (cpBVDV) induce dramatic cytoplasmic vacuolization in cell cultures, while infection with the non-cytopathic (NCP-BVDV) strains produces no overt changes in the host cells. Our results show that extensive cytoplasmic vacuolization is the earliest morphological change in response to cpBVDV infection in MDBK cells. Cells with extensive vacuolization showed no co-existing chromatin condensation, caspase activation, or loss of membrane integrity. In addition, the caspase inhibitor (zVAD-fmk), although improving cell viability of infected cells from 6.7+/-2.2% to 18.8+/-2.2%, did not prevent vacuolization. On the ultrastructural level, the virus-induced cytoplasmic vacuoles are single membrane structures containing organelles and cellular debris, which appear capable of fusing with other vacuoles and engulfing surrounding cytoplasmic materials. LysoTracker Red which marks lysosomes did not stain the virus-induced cytoplasmic vacuoles. In addition, this lysosomal dye could be observed in the cytoplasm of vacuolized cells, suggesting a lysosomal abnormality. Our data demonstrate that cpBVDV induced a novel cell death pathway in MDBK cells that is primarily associated with lysosomal dysfunction and the formation of phagocytic cytoplasmic vacuoles, and this mode of cell death is different from apoptosis and necrosis.

Activation of cell signaling pathways is dependant on the biotype of bovine viral diarrhea viruses type 2

Bovine viral diarrhea virus (BVDV), a pestivirus of the Flaviviridae family, is an economically important cattle pathogen with a worldwide distribution. Besides the segregation into two distinct species (BVDV1/BVDV2) two different biotypes, a cytopathic (cp) and a noncytopathic (ncp) biotype, are distinguished based on their behavior in epithelial cell cultures. One of the most serious forms of BVDV infection affecting immunocompetent animals of all ages is severe acute BVD (sa BVD) which is caused by highly virulent ncp BVDV2 strains. Previous studies revealed that these highly virulent ncp viruses cause cell death in a lymphoid cell line (BL3) which is not clearly associated with typical apoptotic changes (e.g. PARP cleavage) observed after infection with cp BVDV. To further characterize the underlying molecular mechanisms, we first analyzed the role of the mitochondria and caspases as key mediators of apoptosis. Compared to infection with cp BVDV2, infection with highly virulent ncp BVDV2 resulted in a delayed and less pronounced disruption of the mitochondrial transmembrane potential (DeltaPsi(m)) and a weaker activation of the caspase cascade. In contrast, infection with low virulence ncp BVDV2 showed no significant differences from the uninfected control cells. Since different pro- and anti-apoptotic cellular signaling pathways may become activated upon virus infection, we compared the effect of different BVDV2 strains on cellular signaling pathways in BL3 cells. Stress-mediated p38 MAPK phosphorylation was detected only in cells infected with cp BVDV2. Interestingly, infection with highly virulent ncp BVDV2 was found to influence the phosphoinositide 3-kinase (PI3K)-Akt pathway. This indicates that BL3 cells respond differently to infection with BVDV depending on virulence and biotype.

Practical significance of heterogeneity among BVDV strains: Impact of biotype and genotype on U.S. control programs

In the early 1990s research groups in North America noted that a newly recognized severe acute form of bovine viral diarrhea virus infection, referred to as hemorrhagic syndrome or severe acute BVDV (SA BVDV), was associated with a genetically distinct subgroup of BVDV strains. This new subgroup was named BVDV genotype 2 or BVDV2. All BVDV strains previously characterized in the literature belonged to a separate genotype, BVDV1. However, not all strains identified as BVDV2 were associated with severe acute infections. If I did this deletion, I did not mean to do it. I think it was already here, though. I see there are some other big edits that I did not do; fine. Hollis subsequent surveys of BVDV strains isolated from clinical submissions to diagnostic laboratories and contaminated fetal calf serum suggested that the ratio of BVDV2 to BVDV1 strains in the U.S. approached 50%. Further, while antigenic cross reactivity is seen between BVDV1 and BVDV2 strains, a log or more difference is typically observed in titers against viruses from different genotypes. These observations prompted vaccine manufacturers in North America to produce vaccines against BVDV that contained antigens from both BVDV1 and BVDV2 strains. Under experimental conditions, these new vaccines offered improved protection against type 2 strains, however field data are still insufficient to assess their efficacy in practice. The BVDV genotypes may also be segregated into subgenotypes. Two subgenotypes of both BVDV1 (BVDV1a and BVDV1b) and BVDV2 (BVDV2a and BVDV2b) have been reported in North American. BVDV2a predominates with BVDV2b isolation a rare event. In contrast, BVDV1a and BVDV1b are both commonly isolated. Antigenic differences observed between strains from the BVDV1a and BVDV1b subgenotypes have led to the suggestion that protection may be improved by inclusion of strains from both BVDV1a and BVDV1b in vaccines in addition to BVDV2. The cost to benefit ratio of this proposal is currently a matter of debate.

Modulation of PKR activity in cells infected by bovine viral diarrhea virus

Bovine viral diarrhea virus is an important animal pathogen. The cytopathic and noncytopathic biotypes of the virus are associated with distinct pathologic entities. A striking difference between the two biotypes is viral RNA accumulation in infected cells. Viral dsRNA is thought to activate protein kinase PKR; an important mediator of innate immunity. In this study, we investigated PKR activation and its consequences in BVDV-infected cells. Infection with cp BVDV was found to induce PKR activation, eIF2alpha phosphorylation, translation inhibition and NF-kappaB activation. In contrast, PKR activity and eIF2alpha phosphorylation were not induced during infection with the ncp BVDV. In addition, cells infected with ncp BVDV showed no PKR phosphorylation in response to infection with the unrelated poliovirus whereas uninfected ncp BVDV cells when infected with poliovirus showed high levels of phosphorylated PKR. Cells infected with ncp BVDV failed to respond to synthetic dsRNA (poly I:C) treatment with NF-kappaB activation. However, the NF-kappaB response to bacterial lipopolysaccarides (LPS) was normal in these cells, suggesting a specific suppression of antiviral response signaling in ncp BVDV infected cells. These results indicate that ncp BVDV has evolved specific mechanisms to prevent activation of PKR and its antiviral effectors, most likely to facilitate the establishment and maintenance of persistent infection.