BVDV Npro protein mediates the BVDV induced immunosuppression through interaction with cellular S100A9 protein.

The innate immune response is a vital part of the body's antiviral defense system. The innate immune response is initiated by various receptor interactions, including danger associated molecular patterns (DAMPs). The S100A9 is a member of the DAMPs protein family and, is released by activated phagocytic cells such as neutrophils, monocytes, macrophages or endothelial cells, and S100A9 induces its effect through TLR4/MyD88 pathway. Bovine viral diarrhea virus (BVDV) is one of the major devastating disease in the cattle industry worldwide. It shows its effect through immunosuppression and develops persistent infection in calves born from infected cows. The current study revealed that BVDV potentially induced immunosuppression by the interaction of BVDV Npro protein with cellular S100A9 protein. The Inhibition of S100A9 protein expression by small interfering RNA (siRNA) enhanced the virus replication in infected cells. Overexpression of bovine S100A9 enhanced the ncpBVDV2a 1373 mediated Type-I interferon production. A co-immunoprecipitation experiment demonstrated a strong interaction between ncp BVDV2a 1373 Npro protein and cellular S100A9 protein. This suggested that BVDV Npro reduced the S100A9 protein availability/activity in infected cells, resulting in reduced Type-I interferon production. A further study of S100A9-BVDV interaction will be need for better understanding of BVDV pathophysiology.

The effect of bovine viral diarrhea virus (BVDV) strains on bovine monocyte-derived dendritic cells (Mo-DC) phenotype and capacity to produce BVDV.

BACKGROUND: Dendritic cells (DC) are important antigen presentation cells that monitor, process, and present antigen to T cells. Viruses that infect DC can have a devastating impact on the immune system. In this study, the ability of bovine viral diarrhea virus (BVDV) to replicate and produce infectious virus in monocyte-derived dendritic cells (Mo-DC) and monocytes was studied. The study also examined the effect of BVDV infection on Mo-DC expression of cell surface markers, including MHCI, MHCII, and CD86, which are critical for DC function in immune response. METHODS: Peripheral blood mononuclear cells (PBMCs) were isolated from bovine blood through gradient centrifugation. The adherent monocytes were isolated from PBMCs and differentiated into Mo-DC using bovine recombinant interleukin-4 (IL-4) and granulocyte-macrophage colony-stimulating factor (GMCSF). To determine the effect of BVDV on Mo-DC, four strains of BVDV were used including the severe acute non-cytopathic (ncp) BVDV2a-1373; moderate acute ncp BVDV2a 28508-5; and a homologous virus pair [i.e., cytopathic (cp) BVDV1b TGAC and ncp BVDV1b TGAN]. The Cooper strain of bovine herpesvirus 1 (BHV1) was used as the control virus. Mo-DC were infected with one of the BVDV strains or BHV-1 and were subsequently examined for virus replication, virus production, and the effect on MHCI, MHCII, and CD86 expression. RESULTS: The ability of monocytes to produce infectious virus reduced as monocytes differentiated to Mo-DC, and was completely lost at 120 hours of maturation. Interestingly, viral RNA increased throughout the course of infection in Mo-DC, and the viral non-structural (NS5A) and envelope (E2) proteins were expressed. The ncp strains of BVDV down-regulated while cp strain up-regulated the expression of the MHCI, MHCII, and CD86 on Mo-DC. CONCLUSIONS: The study revealed that the ability of Mo-DC to produce infectious virus was reduced with its differentiation from monocytes to Mo-DC. The inability to produce infectious virus may be due to a hindrance of virus packaging or release mechanisms. Additionally, the study demonstrated that ncp BVDV down-regulated and cp BVDV up-regulated the expression of Mo-DC cell surface markers MHCI, MHCII, and CD86, which are important in the mounting of immune responses.

Comparative humoral immune response against cytopathic or non-cytopathic bovine viral diarrhea virus infection.

Bovine viral diarrhea virus (BVDV) infection causes immune dysfunction. The current study investigated the effect of cytopathic (cp) or noncytopathic (ncp) strains of BVDV on immunomodulation by the levels of total serum immunoglobulin G (IgG), the IgG1, IgG2, BVDV neutralizing antibodies and total white blood cell (WBC) count. Twenty (20) BVDV seronegative dairy calves (5-6 months old) were divided in two groups of ten. The animals were infected with either a cp or ncp virus isolated from the same animal (ncp BVDV1b-TGAN or cp BVDV1b-TGAC). One group of 10 was infected with ncp TGAN while the other group of 10 was infected with cp TGAC. Calves infected with cp BVDV had a significant decrease in total IgG as well as IgG1 concentration at 7 days post infection (DPI) that recovered by 21 DPI (total IgG) and 35 DPI (IgG1), respectively. There was no effect of ncp BVDV infection on total IgG concentration in the first 7 days of infection (DOI); however, IgG1 concentration was significantly reduced and IgG2 concentration was significantly increased at 7 DOI. At 35 DPI, ncp TGAN-infected calves had significantly higher total IgG, IgG1 as well as IgG2 compared to cp TGAC-infected calves. Ncp BVDV induced higher BVDV homologous and heterologous neutralizing antibodies compared to the cp BVDV strain. Calves infected with ncp BVDV had significantly reduced WBC counts at 7 DPI that recovered by 14 DPI. Overall, these findings indicate that humoral immunosuppression occurs early following BVDV infection with the largest effect on IgG1 levels.

Bovine viral diarrhea virus multiorgan infection in two white-tailed deer in southeastern South Dakota.

The susceptibility of wild ruminants, especially cervids, to bovine viral diarrhea virus (BVDV) has remained an enigma. Two white-tailed deer (Odocoileus virginianus) were submitted to the Animal Disease Research and Diagnostic Laboratory (ADRDL) in the fall of 2003 by the South Dakota Game Fish and Parks for chronic wasting disease (CWD) testing. Both animals were CWD negative. The animals were necropsied and histopathology, viral antigen detection, and virus isolation were performed. A noncytopathic (NCP) BVDV was isolated from the lungs and several other tissues of both animals. Formalin-fixed ear notches from both animals were positive for BVDV antigen by immunohistochemistry. The BVDV isolates were typed with the use of polymerase chain reaction in 5' untranslated region (UTR) and one isolate was typed a Type 2a and the other a Type 1b. Future field surveys to determine the incidence of BVDV along with experimental studies to determine if white-tailed deer fawns can be persistently infected with BVDV are needed.

Both cytopathic and non-cytopathic bovine viral diarrhea virus (BVDV) induced autophagy at a similar rate.

Autophagy is a cellular process that maintains cellular homeostasis by the proteolytic recycling of cytoplasm. Autophagy occurs at basal levels in almost all cells. It is upregulated in cellular stress including starvation, oxidative stress or during infection. Several viruses including flavivirus have developed strategies to subvert or use autophagy for their efficient replication. Bovine viral diarrhea virus (BVDV) is a member of the Flaviviridae family and the pestivirus virus group. BVDV is responsible for significant economic loss in cattle industry worldwide. A unique characteristic of BVDV is the well-characterized genetic changes that can result in two different phenotypes (biotypes) in cell culture: cytopathic (cp) or non-cytopathic (ncp) effects. The ncp viruses are the most prevalent and important for clinical disease. This study was carried out to determine the effect of different BVDV phenotypes using the virus pair, cp TGAC and ncp TGAN in autophagy induction, as well as to investigate the role of autophagy in BVDV induced cytopathic effect. RESULTS: showed that both biotypes (cp and ncp) of BVDV induced autophagy in immortal Madin-Darby bovine kidney (MDBK) cell line as well as primary bovine turbinate (Bt) cells following infection. There was no significant difference between cp or ncp strains of BVDV in autophagosome formation (p<0.05) in either MDBK or Bt cells. The autophagy inhibiting drug, 3-methyladenine (3MA) significantly reduced autophagy (p<0.05) as well as viral replication. While autophagy inducing drug rapamycin significantly enhanced autophagy as well as viral replication. The co-localization study using, BVDV NS5A, Erns and E1 proteins with autophagy marker, light chain-3 (LC3) revealed that BVDV replication was associated with autophagosomes. This study revealed that both cp and ncp strains of BVDV induced autophagy at similar level and used autophagy machinery for their replication.

Characterization of the cytopathic BVDV strains isolated from 13 mucosal disease cases arising in a cattle herd.

Bovine viral diarrhea virus (BVDV) is a positive single stranded RNA virus belonging to the Pestivirus genus of the Flaviviridae family. BVDV has a wide host range that includes most ruminants. Noncytopathic (ncp) BVDV may establish lifelong persistent infections in calves following infection of the fetus between 40 and 120 days of gestation. Cytopathic (cp) BVDV strains arise from ncp strains via mutations. The most common cp mutations are insertions of RNA derived from either host or a duplication of viral sequences into the region of the genome coding for the NS2/3 protein. Superinfection of a persistently infected animal with a cp virus can give rise to mucosal disease, a condition that is invariably fatal. A herd of 136 bred 3-year old cows was studied. These cows gave birth to 41 PI animals of which 23 succumbed to mucosal disease. In this study, we characterized the ncp and cp viruses isolated from 13 of these animals. All viruses belonged to the BVDV type 2a genotype and were highly similar. All the cp viruses contained an insertion in the NS2/3 coding region consisting of the sequences derived from the transcript encoding a DnaJ protein named Jiv90. Comparison of the inserted DnaJ regions along with the flanking viral sequences in the insertion 3' end of the 13 cp isolates revealed sequence identities ranging from 96% to 99% with common borders. This suggested that one animal likely developed a cp virus that then progressively spread to the other 12 animals. Interestingly, when the inserted mammalian gene replicated within viral genome, it showed conservation of the same conserved motifs between the different species, which may indicate a role for these motifs in the insertion function within the virus genome. This is the first characterization of multiple cp bovine viral diarrhea virus isolates that spread in a herd under natural conditions.

Bovine viral diarrhea virus outbreak in a beef cow herd in South Dakota.

CASE DESCRIPTION: 136 pregnant beef cows were purchased in the fall of 2003. The following spring, 128 cows calved as expected; 8 cows were believed to have aborted with the fetuses unavailable for evaluation. Of the 128 calves born, 8 died within 2 weeks after birth and 9 were born with congenital abnormalities. CLINICAL FINDINGS: Cows and their calves were evaluated for bovine viral diarrhea virus (BVDV) infection. Forty-four of 120 calves, but 0 cows, tested positive for BVDV antigen by immunohistochemical staining of ear notch specimens. TREATMENT AND OUTCOME: Five BVDV test-positive calves died shortly after weaning, and the remaining 39 BVDV test-positive calves were moved to an isolated feedlot and retested for BVDV at 5 to 6 months of age; 36 had positive results, which indicated that they were persistently infected (PI) with BVDV, whereas 3 had negative results, which indicated that they were transiently infected with BVDV at the time of the first test. All PI calves were infected with the same BVDV type 2a strain. As yearlings, 17 of the 36 PI calves died peracutely with lesions consistent with mucosal disease, 6 died without gross lesions, and 2 were euthanized because of chronic ill thrift. The remaining 11 PI calves appeared healthy and were sold for slaughter. Screening of the following year's calf crop for BVDV by use of immunohistochemical staining of ear-notch specimens yielded negative results for all calves. CLINICAL RELEVANCE: Introduction of BVDV into a naïve cow herd resulted in a loss of 44% of the calf crop subsequent to reproductive loss, poor thrift, and mucosal disease.