Porcine reproductive and respiratory syndrome (PRRS) caused by the PRRS virus (PRRSV) is an important swine disease worldwide. PRRSV has a limited tropism for certain cells, which may at least in part be attributed to the expression of the necessary cellular molecules serving as the virus receptors or factors on host cells for virus binding or entry. However, these molecules conferring PRRSV infection have not been fully characterized. Here we show the identification of non-muscle myosin heavy chain 9 (MYH9) as an essential factor for PRRSV infection using the anti-idiotypic antibody specific to the PRRSV glycoprotein GP5. MYH9 physically interacts with the PRRSV GP5 protein via its C-terminal domain and confers susceptibility of cells to PRRSV infection. These findings indicate that MYH9 is an essential factor for PRRSV infection and provide new insights into PRRSV-host interactions and viral entry, potentially facilitating development of control strategies for this important swine disease.

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P orcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically important viruses affecting the swine industry worldwide, resulting in significant economic losses each year (1-3). PRRSV is a small, enveloped, linear, single positive-stranded RNA virus and a member of the order Nidovirales, family Arteriviridae (4). Current vaccination strategies cannot effectively control PRRSV infection because of the high antigenic heterogeneity (5, 6), the replication in and destruction of lung alveolar macrophages (7-9), and the observed antibody-dependent enhancement of PRRSV (10, 11). Therefore, it is imperative to study PRRSV pathogenesis mechanisms so that more effective control measures can be developed.Heme oxygenase-1 (HO-1) is the rate-limiting enzyme of heme degradation, and it functions to catabolize free heme into biliverdin, carbon monoxide, and iron. HO-1 and its end products have antioxidant, anti-inflammatory, and antiviral properties, and it is known to be a pivotal cytoprotective enzyme (12). Upregulation of HO-1 expression suppresses replication of a number of viruses, including hepatitis C virus (HCV), HIV-1, hepatitis B virus (HBV), and influenza virus (13-17). Our previous work showed that PRRSV significantly downregulates HO-1

Porcine reproductive and respiratory syndrome virus (PRRSV) is a continuous threat to the pork industry as it continues to cause significant economic loss worldwide. Currently, vaccination strategies provide very limited protection against PRRSV transmission. Consequently, there is an urgent need to develop new antiviral strategies. Platycodin D (PD) is one of the major bioactive triterpenoid saponins derived from Platycodon grandiflorum, a traditional Chinese medicine used as an expectorant for pulmonary diseases and a remedy for respiratory disorders. Here, we demonstrate that PD exhibits potent activity against PRRSV infection in Marc-145 cells and primary porcine alveolar macrophages. PD exhibited broad-spectrum inhibitory activities in vitro against high pathogenic type 2 PRRSV GD-HD strain and GD-XH strain as well as classical CH-1a and VR2332 strains. PD at concentrations ranging 1–4 μM significantly inhibited PRRSV RNA synthesis, viral protein expression and progeny virus production in a dose-dependent manner. EC50 values of PD against four tested PRRSV strains infection in Marc-145 cells ranged from 0.74 to 1.76 μM. Mechanistically, PD inhibited PRRSV replication by directly interacting with virions therefore affecting multiple stages of the virus life cycle, including viral entry and progeny virus release. In addition, PD decreased PRRSV- and LPS-induced cytokine (IFN-α, IFN-β, IL-1α, IL-6, IL-8 and TNF-α) production in PAMs. Altogether, our findings suggested that PD is a potent inhibitor of PPRSV infection in vitro. However, further in vivo studies are necessary to confirm PD as a potential novel and effective PPRSV inhibitor in swine.

Hepatitis E virus (HEV) causes liver disease in humans and is thought to be a zoonotic infection, with domestic animals, including swine and rabbits, being a reservoir. One of the proteins encoded by the virus is the capsid protein. This is likely the major immune-dominant protein and a target for vaccination. Four monoclonal antibodies (MAbs), three novel, 1E4, 2C7, and 2G9, and one previously characterized, 1B5, were evaluated for binding to the capsid protein from genotype 4 swine HEV. The results indicated that DFCP, PSRPF, and EPTV peptides on the capsid protein comprised minimal amino acid sequence motifs recognized by 1E4, 2C7, and 2G9, respectively. The data suggested that 2C7 and 2G9 epitopes were partially exposed on the surface of the capsid protein. Truncated genotype 4 swine HEV capsid protein (sp239, amino acids 368 to 606) can exist in multimeric forms. Preincubation of swine HEV with 2C7, 2G9, or 1B5 before addition to HepG2 cells partially blocked sp239 cell binding and inhibited swine HEV infection. The study indicated that 2C7, 2G9, and 1B5 partially blocked swine HEV infection of rabbits better than 1E4 or normal mouse IgG. The cross-reactivity of antibodies suggested that capsid epitopes recognized by 2C7 and 2G9 are common to HEV strains infecting most host species. Collectively, MAbs 2C7, 2G9, and 1B5 were shown to recognize three novel linear neutralizing B-cell epitopes of genotype 4 HEV capsid protein. These results enhance understanding of HEV capsid protein structure to guide vaccine and antiviral design. Genotype 3 and 4 HEVs are zoonotic viruses. Here, genotype 4 HEV was studied due to its prevalence in human populations and pig herds in China. To improve HEV disease diagnosis and prevention, a better understanding of the antigenic structure and neutralizing epitopes of HEV capsid protein are needed. In this study, the locations of three novel linear B-cell recognition epitopes within genotype 4 swine HEV capsid protein were characterized. Moreover, the neutralizing abilities of three MAbs specific for this protein, 2C7, 2G9, and 1B5, were studied and Collectively, these findings reveal structural details of genotype 4 HEV capsid protein and should facilitate development of applications for the design of vaccines and antiviral drugs for broader prevention, detection, and treatment of HEV infection of diverse human and animal hosts.

Porcine reproductive and respiratory syndrome (PRRS) is of great concern to the swine industry due to pandemic outbreaks of the disease, current ineffective vaccinations, and a lack of efficient antiviral strategies. In our previous study, a PRRSV Nsp9-specific nanobody, Nb6, was successfully isolated, and the intracellularly expressed Nb6 could dramatically inhibit PRRSV replication in MARC-145 cells. However, despite its small size, the application of Nb6 protein in infected cells is greatly limited, as the protein itself cannot enter the cells physically. In this study, a trans-activating transduction (TAT) peptide was fused with Nb6 to promote protein entry into cells. TAT-Nb6 was expressed as an inclusion body in Escherichia coli, and indirect enzyme-linked immunosorbent assays and pulldown assays showed that E. coli-expressed TAT-Nb6 maintained the binding ability to E. coli-expressed or PRRSV-encoded Nsp9. We demonstrated that TAT delivered Nb6 into MARC-145 cells and porcine alveolar macrophages (PAMs) in a dose- and time-dependent manner, and TAT-Nb6 efficiently inhibited the replication of several PRRSV genotype 2 strains as well as a genotype 1 strain. Using a yeast two-hybrid assay, Nb6 recognition sites were identified in the C-terminal part of Nsp9 and spanned two discontinuous regions (Nsp9aa454–551 and Nsp9aa599–646). Taken together, these results suggest that TAT-Nb6 can be developed as an antiviral drug for the inhibition of PRRSV replication and controlling PRRS disease. IMPORTANCE The pandemic outbreak of PRRS, which is caused by PRRSV, has greatly affected the swine industry. We still lack an efficient vaccine, and it is an immense challenge to control its infection. An intracellularly expressed Nsp9-specific nanobody, Nb6, has been shown to be able to inhibit PRRSV replication in MARC-145 cells. However, its application is limited, because Nb6 cannot physically enter cells. Here, we demonstrated that the cell-penetrating peptide TAT could deliver Nb6 into cultured cells. In addition, TAT-Nb6 fusion protein could suppress the replication of various PRRSV strains in MARC-145 cells and PAMs. These findings may provide a new approach for drug development to control PRRS.

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BackgroundPorcine reproductive and respiratory syndrome virus (PRRSV) could lead to pandemic diseases and huge financial losses to the swine industry worldwide. Curcumin, a natural compound, has been reported to serve as an entry inhibitor of hepatitis C virus, chikungunya virus and vesicular stomatitis virus. In this study, we investigated the potential effect of curcumin on early stages of PRRSV infection.ResultsCurcumin inhibited infection of Marc-145 cells and porcine alveolar macrophages (PAMs) by four different genotype 2 PRRSV strains, but had no effect on the levels of major PRRSV receptor proteins on Marc-145 cells and PAMs or on PRRSV binding to Marc-145 cells. However, curcumin did block two steps of the PRRSV infection process: virus internalization and virus-mediated cell fusion.ConclusionsOur results suggested that an inhibition of genotype 2 PRRSV infection by curcumin is virus strain-independent, and mainly inhibited by virus internalization and cell fusion mediated by virus. Collectively, these results demonstrate that curcumin holds promise as a new anti-PRRSV drug.