Lymphocytopathogenic activity in vitro correlates with high virulence in vivo for BVDV type 2 strains: Criteria for a third biotype of BVDV

Enhanced pathogenicity and synergistic effects of co-infection with bovine viral diarrhea virus 1 and HoBi-like virus in cattle and guinea pigs

Introduction

The Bovine Viral Diarrhea Virus 1 (BVDV1) and HoBi-like virus (BVDV3), both within the same genus, share genomic homology and exhibit low antigenic cross-reactivity despite presenting similar clinical manifestations. In 2021, a bovine respiratory disease complex (BRDC) outbreak on two cattle farms in the Inner Mongolia Autonomous Region of China resulted in ten fatalities.

Methods

Metagenomic and metatranscriptomic analyses were used to identify viral agents, including a co-infection case. A genetic evolution analysis assessed the relationships with related strains. Experimental infections in guinea pigs and calves evaluated the pathogenicity of the viruses.

Results

Phylogenetic analysis of the BVDV3 isolate IM2201 revealed close relatedness to Brazilian strains, with 97.06% nucleotide homology to the highly virulent strain SV478/07. Experimental co-infection in guinea pigs resulted in more severe clinical signs, including fever, cough, diarrhea, and significant pathological changes, and led to a higher mortality rate (40%) compared to no mortality from single-virus infections with BVDV1 or BVDV3. Similarly, co-infected cattle exhibited more severe clinical signs, including bloody diarrhea and rectal temperatures exceeding 40°C, along with persistent viremia and nasal viral shedding from 7 to 21 days post-infection. Blood analysis revealed significant reductions in white blood cell counts, particularly in co-infected cattle.

Discussion

This study highlights the enhanced pathogenicity and synergistic effects of BVDV1 and BVDV3 co-infection, exacerbating disease severity.

Integrative Transcriptomics and Proteomics Analysis Reveals Immune Response Process in Bovine Viral Diarrhea Virus-1-Infected Peripheral Blood Mononuclear Cells

Bovine viral diarrhea virus (BVDV) causes bovine viral diarrhea-mucosal disease, inflicting substantial economic losses upon the global cattle industry. Peripheral blood mononuclear cells (PBMCs) are the central hub for immune responses during host-virus infection and have been recognized as crucial targets for BVDV infection. In order to elucidate the dynamics of host-BVDV-1 interaction, this study harnessed RNA-seq and iTRAQ methods to acquire an extensive dataset of transcriptomics and proteomics data from samples of BVDV-1-infected PBMCs at the 12-h post-infection mark. When compared to mock-infected PBMCs, we identified 344 differentially expressed genes (DEGs: a total of 234 genes with downregulated expression and 110 genes with upregulated expression) and 446 differentially expressed proteins (DEPs: a total of 224 proteins with downregulated expression and 222 proteins with upregulated expression). Selected DEGs and DEPs were validated through quantitative reverse transcriptase-polymerase chain reaction and parallel reaction monitoring. Gene ontology annotation and KEGG enrichment analysis underscored the significant enrichment of DEGs and DEPs in various immunity-related signaling pathways, including antigen processing and presentation, complement and coagulation cascades, cytokine-cytokine receptor interaction, and the NOD-like receptor signaling pathway, among others. Further analysis unveiled that those DEGs and DEPs with downregulated expression were predominantly associated with pathways such as complement and coagulation cascades, the interleukin-17 signaling pathway, cytokine-cytokine receptor interaction, the PI3K-Akt signaling pathway, the tumor necrosis factor signaling pathway, and the NOD-like receptor signaling pathway. Conversely, upregulated DEGs and DEPs were chiefly linked to metabolic pathways, oxidative phosphorylation, complement and coagulation cascades, and the RIG-I-like receptor signaling pathway. These altered genes and proteins shed light on the intense host-virus conflict within the immune realm. Our transcriptomics and proteomics data constitute a significant foundation for delving further into the interaction mechanism between BVDV and its host.

New Insights into the Role and Therapeutic Potential of Heat Shock Protein 70 in Bovine Viral Diarrhea Virus Infection

Bovine viral diarrhea virus (BVDV), a positive-strand RNA virus of the genus Pestivirus in the Flaviviridae family, is the causative agent of bovine viral diarrhea-mucosal disease (BVD-MD). BVDV's unique virion structure, genome, and replication mechanism in the Flaviviridae family render it a useful alternative model for evaluating the effectiveness of antiviral drugs used against the hepatitis C virus (HCV). As one of the most abundant and typical heat shock proteins, HSP70 plays an important role in viral infection caused by the family Flaviviridae and is considered a logical target of viral regulation in the context of immune escape. However, the mechanism of HSP70 in BVDV infection and the latest insights have not been reported in sufficient detail. In this review, we focus on the role and mechanisms of HSP70 in BVDV-infected animals/cells to further explore the possibility of targeting this protein for antiviral therapy during viral infection.

Non-cytopathic bovine viral diarrhoea virus 2 induces autophagy to enhance its replication

BACKGROUND

Bovine viral diarrhoea virus (BVDV) is an important viral pathogen that has an economic impact on the livestock industry worldwide. Autophagy is one of the earliest cell-autonomous defence mechanisms against microbial invasion, and many types of viruses can induce autophagy by infecting host cells.

OBJECTIVES

The aim of this study was to identify the role of autophagy in the pathogenesis of non-cytopathic (ncp) BVDV2 infection.

METHODS

Madin-Darby bovine kidney (MDBK) cells were treated with ncp BVDV2, rapamycin, or 3-methyladenine (MA) and ncp BVDV2 and then incubated at 37°C for 24 h. Cells were harvested, and the effects of autophagy were determined by transmission electron microscopy (TEM), confocal laser microscopy, western blotting and qRT-PCR. Apoptotic analysis was also performed using western blotting and flow cytometry.

RESULTS

In ncp BVDV2-infected MDBK cells, more autophagosomes were observed by TEM, and the number of microtubule-associated protein 1 light chain 3B (LC3B) with green fluorescent protein puncta was also increased. The ncp BVDV2-infected cells showed significantly enhanced conversion of LC3-I to LC3-II, as well as upregulation of autophagy-related proteins, including ATG5 and Beclin 1, and substantial degradation of p62/SQSTM1. These results are similar to those induced by rapamycin, an autophagy inducer. E2 protein expression, which is associated with viral replication, increased over time in ncp BVDV2-infected cells. Inhibition of autophagy by 3-MA in ncp BVDV2-infected MDBK cells downregulated the expressions of LC3-II, ATG5 and Beclin 1 and prevented the degradation of p62/SQSTM1. Moreover, the expressions of phosphorylated Akt and procaspase-3 were significantly increased in ncp BVDV2-infected cells. In addition, the mRNA level of protein kinase R (PKR) was significantly reduced in ncp BVDV2-infected cells.

CONCLUSIONS

Our results demonstrate that ncp BVDV2 infection induced autophagy in MDBK cells via anti-apoptosis and PKR suppression. Therefore, autophagy may play a role in establishing persistent infection caused by ncp BVDV.

Bovine viral diarrhea virus compromises Neutrophil's functions in strain dependent manner

Bovine viral diarrhea virus (BVDV) infection is a major problem that results in economically important diseases of the cattle industry worldwide. The two major consequences of this disease are persistent infection and immune dysfunction. A number of studies have been done to determine the underline mechanisms of BVDV-induced immune dysfunction, in particular targeting antigen-presenting cells, T- and B- cells and cytokine gene expression. However, little research has focused Eon the effect of BVDV on neutrophils. Neutrophils are one of the predominant leukocytes circulating in blood and are considered the first line of defense in the innate immune system along with macrophages. Neutrophils not only eliminate the invading bacteria but also activate innate as well as adaptive immune responses. Therefore, compromised neutrophil function would affect both arms of immune system and caused immune suppression. In the current study, we used virus strains from both BVDV-1 and BVDV-2 species. Including a highly virulent non-cytopathic type 2a BVDV (ncp BVDV2a-1373), moderately virulent non-cytopathic type 2a (ncp BVDV2a 28508-5), and a pair of non-cytopathic type 1b BVDV (ncp BVDV1b TGAN) and cytopathic type 1b BVDV (cp BVDV1b TGAC) strain isolated from a case of mucosal disease. The highly virulent ncp BVDV2a-1373 significantly increased neutrophil apoptosis. However, none of the other BVDV strains affected neutrophil viability. All BVDV strains used significantly reduced CD18 and L-selectin expression on neutrophils as well as their oxidative burst and neutrophil extracellular traps (NET) activity. Cp BVDV significantly reduced neutrophil's phagocytic activity but ncp BVDV did not have any effect on it. On the other hand, ncp BVDV significantly increased neutrophil's CD14 expression and chemotactic activity while cp BVDV did not show any effect either on neutrophil's CD14 expression or on chemotactic activity. In conclusion, BVDV affected neutrophils variability and functional activity in strain dependent manner. Results of the current study will further help in understanding the pathophysiology of different BVDV strains.

The Effect of Bovine Viral Diarrhea Virus (BVDV) Strains and the Corresponding Infected-Macrophages' Supernatant on Macrophage Inflammatory Function and Lymphocyte Apoptosis

Bovine viral diarrhea virus (BVDV) is an important viral disease of cattle that causes immune dysfunction. Macrophages are the key cells for the initiation of the innate immunity and play an important role in viral pathogenesis. In this in vitro study, we studied the effect of the supernatant of BVDV-infected macrophage on immune dysfunction. We infected bovine monocyte-derived macrophages (MDM) with high or low virulence strains of BVDV. The supernatant recovered from BVDV-infected MDM was used to examine the functional activity and surface marker expression of normal macrophages as well as lymphocyte apoptosis. Supernatants from the highly virulent 1373-infected MDM reduced phagocytosis, bactericidal activity and downregulated MHC II and CD14 expression of macrophages. Supernatants from 1373-infected MDM induced apoptosis in MDBK cells, lymphocytes or BL-3 cells. By protein electrophoresis, several protein bands were unique for high-virulence, 1373-infected MDM supernatant. There was no significant difference in the apoptosis-related cytokine mRNA (IL-1beta, IL-6 and TNF-a) of infected MDM. These data suggest that BVDV has an indirect negative effect on macrophage functions that is strain-specific. Further studies are required to determine the identity and mechanism of action of these virulence factors present in the supernatant of the infected macrophages.

PD-1-Mediated PI3K/Akt/mTOR, Caspase 9/Caspase 3 and ERK Pathways Are Involved in Regulating the Apoptosis and Proliferation of CD4+ and CD8+ T Cells During BVDV Infection in vitro

Acute infection of bovine viral diarrhea virus (BVDV) is associated with immune dysfunction and can cause peripheral blood lymphopenia and lymphocyte apoptosis. Our previous study has confirmed that programmed death-1 (PD-1) blockade inhibits peripheral blood lymphocyte (PBL) apoptosis and restores proliferation and anti-viral immune functions of lymphocytes after BVDV infection in vitro. However, the immunomodulatory effects of PD-1 pathway on major PBL subsets are unclear and their underlying molecular mechanisms need to be further studied. Therefore, in this study, we examined PD-1 expression in bovine PBL subsets after BVDV infection in vitro and analyzed the effects of PD-1 blockade on the apoptosis and proliferation of CD4⁺ and CD8⁺ T cells and expression of PD-1 downstream signaling molecules. The results showed that PD-1 expression was enhanced on CD4⁺ and CD8⁺ T cells, but not on CD21⁺ B cells after cytopathic (CP) BVDV (strain NADL) and non-cytopathic (NCP) BVDV (strain KD) infection in vitro and PD-1 blockade significantly reduced the apoptosis of CD4⁺ and CD8⁺ T cells after these two strains infection. Remarkably, PD-1 blockade significantly increased the proliferation of CD4⁺ and CD8⁺ T cells after CP BVDV infection, but only significantly increased the proliferation of CD4⁺ T cells after NCP BVDV infection. In addition, we confirmed that PD-1-mediated PI3K/Akt/mTOR, caspase 9/caspase 3 and ERK pathways are involved in regulating the apoptosis and proliferation of CD4⁺ and CD8⁺ T cells during BVDV infection in vitro. Notably, ERK is involved in the regulation mechanism PD-1 mediated only when the cells are infected with CP BVDV. Our findings provide a scientific basis for exploring the molecular mechanism of immune dysfunction caused by acute BVDV infection.

In vitro method to evaluate virus competition between BVDV-1 and BVDV-2 strains using the PrimeFlow RNA assay

Bovine viral diarrhea viruses (BVDV), segregated in BVDV-1 and BVDV-2 species, lead to substantial economic losses to the cattle industry worldwide. It has been hypothesized that there could be differences in level of replication, pathogenesis and tissue tropism between BVDV-1 and BVDV-2 strains. Thus, this study developed an in vitro method to evaluate virus competition between BVDV-1 and BVDV-2 strains. To this end the competitive dynamics of BVDV-1a, BVDV-1b, and BVDV-2a strains in cell cultures was evaluated by a PrimeFlow RNA assay. Similar results were observed in this study, as was observed in an earlier in vivo transmission study. Competitive exclusion was observed as the BVDV-2a strains dominated and excluded the BVDV-1a and BVDV-1b strains. The in vitro model developed can be used to identify viral variations that result in differences in frequency of subgenotypes detected in the field, vaccine failure, pathogenesis, and strain dependent variation in immune responses.

PD-1 blockade inhibits lymphocyte apoptosis and restores proliferation and anti-viral immune functions of lymphocyte after CP and NCP BVDV infection in vitro

Bovine viral diarrhea virus (BVDV) is an important virus that can cause extensive economic losses in both dairy and beef industry worldwide. Acute infection with BVDV results in peripheral blood lymphopenia, apoptosis and immunosuppression. Up-regulated programmed death-1 (PD-1) expression induces functional exhaustion of lymphocytes, inhibition of proliferation and apoptosis of lymphocytes during acute and chronic viral infections, such as HIV and HCV. However, there are no reports showing the role of PD-1 in peripheral blood lymphopenia, apoptosis and immunosuppression after acute BVDV infection. Accordingly, we measured the mRNA and protein expression of PD-1 and programmed death-ligand 1 (PD-L1) in peripheral blood mononuclear cells (PBMCs) infected with BVDV, and analyzed the effects of PD-1 blockade on immune-associated function and activity in peripheral blood lymphocytes (PBLs). The results showed that both cytopathic (CP) BVDV (strain NADL) and non-cytopathic (NCP) BVDV (strain KD) infection stimulated the mRNA and protein expression of PD-1 and PD-L1 significantly. The upregulation of PD-1/PD-L1 was accompanied by the decreased PBLs proliferation and increased apoptosis. Additionally, PD-1 blockade restored proliferation, inhibited apoptosis, increased IFN-γ production and decreased BVDV load. Remarkably, the PD-1/PD-L1 interaction has a more substantial effect on the immunoregulation of inhibiting proliferation induced by CP BVDV infection. Our findings confirm that PD-1 plays a vital role in peripheral blood lymphopenia and apoptosis caused by acute BVDV infection, and provide new insights into exploring the immunopathological mechanisms of BVDV or other members of the Flaviviridae family, and a potential therapeutic strategy to control BVDV infection.

In Vitro and In Vivo Characterization of a Typical and a High Pathogenic Bovine Viral Diarrhea Virus Type II Strains

Non-cytopathic (ncp) type 2 bovine viral diarrhea virus (BVDV-2) is widely prevalent in Argentina causing high mortality rates in cattle herds. In this study, we characterized an Argentinean ncp BVDV-2 field isolate (98-124) compared to a high-virulence reference strain (NY-93), using in silico analysis, in vitro assays, and in vivo infections of colostrum-deprived calves (CDC) to compare pathogenic characters and virulence. In vitro infection of bovine peripheral blood mononuclear cells (PBMC) with BVDV 98-124 induced necrosis shortly after infection while NY-93 strain increased the apoptotic rate in infected cells. Experimental infection of CDC (n = 4 each) with these strains caused an enteric syndrome. High pyrexia was detected in both groups. Viremia and shedding were more prolonged in the CDC infected with the NY-93 strain. In addition, NY-93 infection elicited a severe lymphopenia that lasted for 14 days, whereas 98-124 strain reduced the leukocyte counts for 5 days. All infected animals had a diminished lymphoproliferation activity in response to a mitogen. Neutralizing and anti-NS3 antibodies were detected 3 weeks after infection in all infected calves. Virulence was associated with a more severe clinical score, prolonged immune-suppression, and a greater window for transmission. Studies of apoptosis/necrosis performed after in vitro PBMC infection also revealed differences between both strains that might be correlated to the in vivo pathogenesis. Our results identified 98-124 as a low-virulence strain.

Forsythoside A Inhibits BVDV Replication via TRAF2-Dependent CD28-4-1BB Signaling in Bovine PBMCs

Bovine viral diarrhea virus (BVDV), the causative agent of bovine viral diarrhea/mucosal disease (BVD/MD), is an important pathogen of cattle and other wild animals throughout the world. BVDV infection typically leads to an impaired immune response in cattle. In the present study, we investigated the effect of Forsythoside A (FTA) on BVDV infection of bovine peripheral blood mononuclear cells (PBMCs). We found that Forsythoside A could not only promote proliferation of PBMCs and T cells activation but also inhibit the replication of BVDV as well as apoptosis induced by BVDV. FTA treatment could counteract the BVDV-induced overproduction of IFN-γ to maintain the immune homeostasis in bovine PBMCs. At same time, FTA can enhance the secretion of IL-2. What's more, BVDV promotes the expression of CD28, 4-1BB and TRAF-2, which can be modulated by FTA. Our data suggest that FTA protects PBMCs from BVDV infection possibly via TRAF2-dependent CD28-4-1BB signaling, which may activate PBMCs in response to BVDV infection. Therefore, this aids in the development of an effective adjuvant for vaccines against BVDV and other specific FTA-based therapies for preventing BVDV infection.

Bovine Viral Diarrhea Virus Type 2 Impairs Macrophage Responsiveness to Toll-Like Receptor Ligation with the Exception of Toll-Like Receptor 7

Bovine viral diarrhea virus (BVDV) is a member of the Flaviviridae family. BVDV isolates are classified into two biotypes based on the development of cytopathic (cp) or non-cytopathic (ncp) effects in epithelial cell culture. BVDV isolates are further separated into species, BVDV1 and 2, based on genetic differences. Symptoms of BVDV infection range from subclinical to severe, depending on strain virulence, and may involve multiple organ systems and induction of a generalized immunosuppression. During BVDV-induced immune suppression, macrophages, critical to innate immunity, may have altered pathogen recognition receptor (PRR) signaling, including signaling through toll-like receptors (TLRs). Comparison of BVDV 2 strains with different biotypes and virulence levels is valuable to determining if there are differences in host macrophage cellular responses between viral phenotypes. The current study demonstrates that cytopathic (cp), noncytopathic (ncp), high (hv) or low virulence (lv) BVDV2 infection of bovine monocyte-derived macrophages (MDMΦ) result in differential expression of pro-inflammatory cytokines compared to uninfected MDMΦ. A hallmark of cp BVDV2 infection is IL-6 production. In response to TLR2 or 4 ligation, as might be observed during secondary bacterial infection, cytokine secretion was markedly decreased in BVDV2-infected MDMΦ, compared to non-infected MDMΦ. Macrophages were hyporesponsive to viral TLR3 or TLR8 ligation. However, TLR7 stimulation of BVDV2-infected MDMΦ induced cytokine secretion, unlike results observed for other TLRs. Together, these data suggest that BVDV2 infection modulated mRNA responses and induced a suppression of proinflammatory cytokine protein responses to TLR ligation in MDMΦ with the exception of TLR7 ligation. It is likely that there are distinct differences in TLR pathways modulated following BVDV2 infection, which have implications for macrophage responses to secondary infections.

Immune response to bovine viral diarrhea virus--looking at newly defined targets

Bovine viral diarrhea virus (BVDV) has long been associated with a wide variety of clinical syndromes and immune dysregulation, many which result in secondary bacterial infections. Current understanding of immune cell interactions that result in activation and tolerance are explored in light of BVDV infection including: depletion of lymphocytes, effects on neutrophils, natural killer cells, and the role of receptors and cytokines. In addition, we review some new information on the effect of BVDV on immune development in the fetal liver, the role of resident macrophages, and greater implications for persistent infection.

Noncytopathic bovine viral diarrhea virus 2 impairs virus control in a mouse model

Bovine viral diarrhea virus (BVDV) is an economically important pathogen that causes development of mild to severe clinical signs in wild and domesticated ruminants. We previously showed that mice could be infected by BVDV. In the present study, we infected mice intraperitoneally with non-cytopathic (ncp) BVDV1 or ncp BVDV2, harvested the blood and organs of the infected mice at days 4, 7, 10 and 14 postinfection (pi), and performed immunohistochemical analyses to confirm BVDV infection. Viral antigens were detected in the spleens of all infected mice from days 4 through 14 and were also found in the mesenteric lymph nodes, gut-associated lymphoid tissue (GALT), heart, kidney, intestine, and bronchus-associated lymphoid tissue (BALT) of some infected mice. In ncp BVDV2-infected mice, flow cytometric analysis revealed markedly fewer CD4(+) and CD8(+) T lymphocytes and lower expression of costimulatory molecules CD80 (B7-1) and CD86 (B7-2) and major histocompatibility complex (MHC) class II (I-A/I-E) than those in ncp BVDV1-infected mice. Production of the cytokines interleukin (IL)-6 and monocyte chemotactic protein (MCP)-1 was higher in the plasma of ncp BVDV2-infected mice than that in that of ncp BVDV1-infected mice. Our results demonstrate that ncp BVDV1 and ncp BVDV2 interact differently with the host innate immune response in vivo. These findings highlight an important distinction between ncp BVDV1 and ncp BVDV2 and suggest that ncp BVDV2 impairs the host's ability to control the infection and enhances virus dissemination.

Experimental infection with cytopathic bovine viral diarrhea virus in mice induces megakaryopoiesis in the spleen and bone marrow

Here, we infected mice with cytopathic bovine viral diarrhea virus 1 (cp BVDV1) by oral inoculation and investigated the effects of infection by histopathological, immunohistochemical (IHC), hematological methods. Twelve mice were infected, and samples were obtained at day 2, 5, and 9 postinfection (pi). Most of the infected mice exhibited clinical signs of illness such as reduced movement, crouching, loose feces, loss of appetite, and reduced water intake. Blood samples from six mice were positive for BVDV based on reverse transcription polymerase chain reaction (RT-PCR). Blood analysis also revealed thrombocytopenia and lymphopenia. Viral antigens were detected in the spleen (12/12), bone marrow (12/12), and/or mesenteric lymph nodes (4/12) of all infected mice by IHC analysis. The spleens showed significant histopathological changes including (i) substantially increased numbers of megakaryocytes, (ii) lymphocyte depletion, and (iii) hemorrhages. The bone marrow also had an increased number of megakaryocytes, although this increase was not as strong as it was in the spleen. Severe lymphoid depletion was observed in the mesenteric lymph nodes. Viral infections were present in the lymphocytes but not detected in megakaryocytes of the spleen, bone marrow, or mesenteric lymph nodes. These results suggest that the increased numbers of megakaryocytes may be a direct result of BVDV infection. BVDV infection in mice following oral inoculation of cp BVDV1 leads to megakaryopoiesis in the spleen and bone marrow to replenish the platelets.

Acute infection with bovine viral diarrhea virus of low or high virulence leads to depletion and redistribution of WC1(+) γδ T cells in lymphoid tissues of beef calves

The objective of this study was to determine the abundance and distribution of γδ T lymphocytes in lymphoid tissue during acute infection with high (HV) or low virulence (LV) non-cytopathic bovine viral diarrhea virus (BVDV) in beef calves. This study was performed using tissue samples from a previous experiment in which thirty beef calves were randomly assigned to 1 of 3 groups: LV [n=10; animals inoculated intranasally (IN) with LV BVDV-1a (strain SD-1)], HV [n=10; animals inoculated IN with HV BVDV-2 (strain 1373)], and control (n=10; animals inoculated with cell culture medium). On day 5 post inoculation, animals were euthanized, and samples from spleen and mesenteric lymph nodes (MLN) were collected to assess the abundance of WC1(+) γδ T cells. A higher proportion of calves challenged with BVDV showed signs of apoptosis and cytophagy in MLN and spleen samples compared to the control group. A significantly lower number of γδ T cells was observed in spleen and MLN from calves in HV and LV groups than in the control calves (P<0.05). In conclusion, acute infection with HV or LV BVDV resulted in depletion of WC1(+) γδ T cells in mucosal and systemic lymphoid tissues at five days after challenge in beef calves. This reduction in γδ T cells in the studied lymphoid tissues could be also due to lymphocyte trafficking to other tissues.

Analysis of mRNA expression for genes associated with regulatory T lymphocytes (CD25, FoxP3, CTLA4, and IDO) after experimental infection with bovine viral diarrhea virus of low or high virulence in beef calves

Immunosuppression caused by bovine viral diarrhea virus (BVDV) has been associated with lymphocyte depletion, leukopenia and impairment of leukocyte function; however, no work has been done on the relationship between BVDV and regulatory T lymphocytes (Tregs). The objective of this study was to compare the mRNA expression of genes associated with Tregs (CD25, FoxP3, CTLA4, and IDO), after experimental infection of beef calves with low (LV) or high (HV) virulence BVDV. Thirty BVDV-naïve calves were randomly assigned to three groups. Calves were intra-nasally inoculated with LV (n=10, strain SD-1) or HV (n=10, strain 1373) BVDV or BVDV-free cell culture medium (control, n=10). Quantitative RT-PCR was used to determine the expression of target genes in tracheo-bronchial lymph nodes and spleen on day 5 post-infection. The mRNA expression of CD25 was up-regulated in tracheo-bronchial lymph nodes of LV (P<0.05), but not in HV compared to the control group. The expression of FoxP3 and CTLA4 was not increased in tracheo-bronchial lymph nodes of either of the BVDV-inoculated groups. A dramatic up-regulation of IDO mRNA was observed in tracheo-bronchial lymph nodes of LV (P<0.05), but not HV compared to the control calves. In conclusion, experimental infection with BVDV did not provide evidence of Treg activation based on expression of FoxP3 and CTL4. Differential expression of CD25 and IDO mRNA on day 5 post-infection with HV or LV BVDV might reflect temporal differences in transcription occurring during the immune response elicited by these viral strains, or differences in viral infectivity of the host cells.

Expression of type I interferon-induced antiviral state and pro-apoptosis markers during experimental infection with low or high virulence bovine viral diarrhea virus in beef calves

The objective of this study was to compare the mRNA expression of host genes involved in type-I interferon-induced antiviral state (IFN-α, IFN-β, Mx-1, PKR, OAS-1 and ISG-15), and apoptosis (caspase-3, -8, and -9), after experimental infection of beef calves with low or high virulence noncytopathic (ncp) bovine viral diarrhea virus (BVDV) strains. Thirty BVDV-naïve, clinically normal calves were randomly assigned to three groups. Calves were intranasally inoculated with low (LV; n=10, strain SD-1) or high (HV; n=10, strain 1373) virulence ncp BVDV or BVDV-free cell culture medium (Control, n=10). Quantitative RT-PCR was used to determine the target gene expression in tracheo-bronchial lymph nodes and spleen 5 days after infection. Interferon-α and -β mRNA levels were up-regulated in tracheo-bronchial lymph nodes (P<0.05) in the HV group, but not in the LV group, compared with the control group. There was an up-regulation of type I interferon-induced genes in spleen and tracheo-bronchial lymph nodes of HV and LV groups, compared with the control group (P<0.01). mRNA levels of OAS-1 and ISG-15 were significantly higher in LV than HV calves (P<0.05). A significant up-regulation of caspase-8 and -9 was observed in tracheo-bronchial lymph nodes in the LV group (P=0.01), but not in the HV group. In conclusion, experimental infection with either high or low virulence BVDV strains induced a significant expression of the type I interferon-induced genes in beef calves. There was a differential expression of some interferon-induced genes (OAS-1 and ISG-15) and pro-apoptosis markers based on BVDV virulence and genotype.

The impact of BVDV infection on adaptive immunity

Bovine viral diarrhea virus (BVDV) causes immunosuppression of the adaptive immune response. The level of suppression of the adaptive immune response is strain dependent. The early events of antigen presentation require activation of toll-like receptors that results in the release of pro-inflammatory cytokines. Non-cytopathic (ncp) BVDV infection stimulates cytokines from macrophages in vitro but the effect of BVDV infection in vivo on macrophages or in vitro with monocytes is not clear. Antigen presentation is decreased and co-stimulatory molecules are down regulated. T-lymphocytes numbers are reduced following BVDV infection in a strain dependent manner. There is recruitment of lymphocytes to the bronchial alveolar space following cytopathic (cp) BVDV infection. Depletion of T-lymphocytes occurs in the lymphoid tissue and is strain dependent. BVDV cp T-lymphocyte responses appear to be primarily a T helper 1 response while the response following ncp BVDV induces a T helper 2 response. Cytotoxic T-lymphocytes (CTL), an important BVDV defense mechanism are compromised. The major neutralizing antigens are well characterized but cross-protection between strains is variable. PI animals have normal adaptive immune responses with the exception of the PI strain immunotolerance and mucosal disease may be a function of the level of gamma delta T cells.

Evaluation of the onset of protection induced by a modified-live virus vaccine in calves challenge inoculated with type 1b bovine viral diarrhea virus

OBJECTIVE

To evaluate onset of protection induced by modified-live virus (MLV) bovine viral diarrhea virus (BVDV) vaccine administered 7, 5, or 3 days before inoculation with type 1b BVDV (strain NY-1). Animals-40 calves.

PROCEDURES

Calves were assigned to 4 groups: an unvaccinated control group or groups vaccinated with MLV vaccine containing BVDV types 1a and 2 at 7, 5, or 3 days, before inoculation with NY-1 BVDV. Blood samples were collected for leukocyte counts, serum virus neutralization, and virus isolation (VI); nasal swab specimens (NSSs) were obtained for VI, and rectal temperatures were monitored for 14 days after inoculation.

RESULTS

No significant differences in leukocyte counts or rectal temperatures were detected after BVDV inoculation in vaccinated calves. Vaccinated calves had reduced viremia and viral shedding after inoculation, compared with results for unvaccinated calves. On day 5 after inoculation, a higher proportion of calves vaccinated 3 days before inoculation had positive VI from NSSs, compared with NSS VI results for calves vaccinated 5 and 7 days before inoculation. Unvaccinated calves had leukopenia on days 3, 5, and 6 and had higher rectal temperatures on days 7 and 8 after inoculation, compared with temperatures before inoculation. All unvaccinated calves had ≥ 1 positive VI result from NSSs 3 to 11 days after inoculation, and 4 became viremic.

CONCLUSIONS AND CLINICAL RELEVANCE

MLV BVDV vaccine prevented fever, viremia, and leukopenia in calves challenge inoculated with NY-1 BVDV. A high proportion of calves vaccinated 3 days before inoculation shed BVDV after inoculation.

Virus Distribution and Role of Thymic Macrophages During Experimental Infection With Noncytopathogenic Bovine Viral Diarrhea Virus Type 1

Thymic depletion, presence of viral antigen, and changes in distribution and cytokine production of thymic macrophages were investigated in calves experimentally infected with a noncytopathogenic bovine viral diarrhea virus type (BVDV) 1 strain. Ten clinically healthy colostrum-deprived calves were used. Eight calves were inoculated with the virus and two were used as uninfected controls. Calves were sedated and euthanized in batches between 3 and 14 days postinoculation. At necropsy, thymus samples were collected for structural, immunohistochemical, and ultrastructural study and TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling). From 6 days postinoculation, the thymic cortex was multifocally depleted with increased frequency of pyknosis and karyorrhexis, suggestive of apoptosis and confirmed by the TUNEL technique. Although the onset of lymphoid depletion was coincident with the detection of viral antigen by immunohistochemistry, the number of infected lymphocytes was very low through the experiment. There was an increase in number of macrophages in cortex and medulla, accompanied by ultrastructural changes indicative of phagocyte activation, and a decrease in cells expressing tumor necrosis factor-alpha (TNF-α) and IL-1α. These results suggest that the increase in number of these cells could be related to phagocytosis of cell debris and apoptotic lymphocytes. Furthermore, the results imply that, in contrast to the situation with classical swine fever virus, the lymphocyte apoptosis resulting from bovine viral diarrhea virus infection is not mediated by TNF-α or interleukin-1 alpha (IL-1α) production by virus-infected macrophages. This is the first study that describes this decrease in the number of thymic cells expressing TNF-α and IL-1α in cattle experimentally infected with bovine viral diarrhea virus type 1.

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.

Validation of endogenous reference genes for RT-qPCR normalisation in bovine lymphoid cells (BL-3) infected with Bovine Viral Diarrhoea Virus (BVDV)

Reverse transcription quantitative PCR (RT-qPCR) is a highly sensitive tool that can be used for accurate and reliable gene expression analysis; however, careful normalisation to a set of stably expressed endogenous reference genes is essential. Expression levels of many reference genes in RT-qPCR analyses can be extremely variable under different experimental conditions, producing potentially erroneous results (Bustin, 2002). This limitation can be overcome with a systematic evaluation of candidate reference genes to determine the most stable. In the present study eight candidate reference genes were evaluated in a bovine lymphoid (BL-3) cell culture system over seven different time points in response to three different Bovine Viral Diarrhoea Virus (BVDV) strains. Data were analysed using BestKeeper (Pfaffl et al., 2004), geNorm (Vandesompele et al., 2002), and NormFinder (Andersen et al., 2004) validation programs and results enable the candidate reference genes to be ranked from most to least stable. Quantification cycle (C(q)) variability was determined between samples, i.e. between treatment groups and time points, and variability was also observed between the three validation programs. The reference gene combination of beta-actin and hypoxanthine-guanine phosphoribosyl transferase (HPRT) was found to be the most stable in Norm Finder. BestKeeper and geNorm both demonstrated beta-microglobulin and tyrosine 3-monooxygenase/tryptophan 5-monooxygenase (YWHAZ) as the most stable. The determination of a stable set of reference genes in the BL-3 cell culture system facilitates analysis of expression levels for appropriate genes of interest. This study further emphasises the need to accurately validate candidate reference genes before use in gene expression RT-qPCR studies.

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.

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.