Bergamottin Inhibits PRRSV Replication by Blocking Viral Non-Structural Proteins Expression and Viral RNA Synthesis

The porcine reproductive and respiratory syndrome virus (PRRSV) causes economic losses in the swine industry worldwide. However, current vaccines cannot provide effective protection against PRRSV, and PRRSV-specific treatments for infected herds are still unavailable. In this study, we found that bergamottin showed strong inhibitory effects against PRRSV replication. Bergamottin inhibited PRRSV at the stage of the replication cycle. Mechanically, bergamottin promoted the activation of IRF3 and NF-κB signaling, leading to the increased expression of proinflammatory cytokines and interferon, which inhibited viral replication to some extent. In addition, bergamottion could reduce the expression of the non-structural proteins (Nsps), leading to the interruption of replication and transcription complex (RTC) formation and viral dsRNA synthesis, ultimately restraining PRRSV replication. Our study identified that bergamottin possesses potential value as an antiviral agent against PRRSV in vitro.

Testable Candidate Immune Correlates of Protection for Porcine Reproductive and Respiratory Syndrome Virus Vaccination

Porcine reproductive and respiratory syndrome virus (PRRSV) is an on-going problem for the worldwide pig industry. Commercial and experimental vaccinations often demonstrate reduced pathology and improved growth performance; however, specific immune correlates of protection (CoP) for PRRSV vaccination have not been quantified or even definitively postulated: proposing CoP for evaluation during vaccination and challenge studies will benefit our collective efforts towards achieving protective immunity. Applying the breadth of work on human diseases and CoP to PRRSV research, we advocate four hypotheses for peer review and evaluation as appropriate testable CoP: (i) effective class-switching to systemic IgG and mucosal IgA neutralizing antibodies is required for protective immunity; (ii) vaccination should induce virus-specific peripheral blood CD4+ T-cell proliferation and IFN-γ production with central memory and effector memory phenotypes; cytotoxic T-lymphocytes (CTL) proliferation and IFN-γ production with a CCR7- phenotype that should migrate to the lung; (iii) nursery, finishing, and adult pigs will have different CoP; (iv) neutralizing antibodies provide protection and are rather strain specific; T cells confer disease prevention/reduction and possess greater heterologous recognition. We believe proposing these four CoP for PRRSV can direct future vaccine design and improve vaccine candidate evaluation.

Major Vault Protein Inhibits Porcine Reproductive and Respiratory Syndrome Virus Infection in CRL2843CD163 Cell Lines and Primary Porcine Alveolar Macrophages

Porcine reproductive and respiratory syndrome (PRRS), a significant viral infectious disease that commonly occurs among farmed pigs, leads to considerable economic losses to the swine industry worldwide. Major vault protein (MVP) is a host factor that induces type Ⅰ interferon (IFN) production. In this study, we evaluated the effect of MVP on PRRSV infection in CRL2843^CD163 cell lines and porcine alveolar macrophages (PAMs). Our results showed that MVP expression was downregulated by PRRSV infection. Adenoviral overexpression of MVP inhibited PRRSV replication, whereas the siRNA knockdown of MVP promoted PRRSV replication. In addition, MVP knockdown has an adverse effect on the inhibitive role of MVP overexpression on PRRSV replication. Moreover, MVP could induce the expression of type Ⅰ IFNs and IFN-stimulated gene 15 (ISG15) in PRRSV-infected PAMs. Based on these results, MVP may be a potential molecular target of drugs for the effective prevention and treatment of PRRSV infection.

Lipopolysaccharide Downregulates CD163 Expression to Inhibit PRRSV Infection via TLR4-NF-κB Pathway

Porcine reproductive and respiratory syndrome virus (PRRSV) has been recognized to induce proinflammatory cytokine production and modulate the host interferon (IFN) system. Proinflammatory cytokines and type I IFNs contribute to the prevention of viral infection. Lipopolysaccharide (LPS), a specific agonist to Toll-like receptor 4 (TLR4), provokes signal transduction and activates immune response in vivo and in vitro. Here we identified LPS inhibited PRRSV infection in porcine alveolar macrophages (PAMs) and in Marc-145 cells. To investigate the possible mechanism, we found TLR4-NF-κB pathway was obviously activated in LPS-treated PAMs at the early stage of PRRSV infection. As a result, the expression of proinflammatory cytokines was strongly induced following LPS and PRRSV co-treatment. Due to the enhanced proinflammatory response, CD163 expression was significantly reduced and a disintegrin and metalloproteinase 17 was activated, which promotes the cleavage of membrane CD163. Ultimately, CD163 down-regulation led to the suppression of PRRSV replication. Our data demonstrate that LPS has an impact on PRRSV infection via inflammation response, which provides a new insight of inflammation-mediated antiviral immunity and a new strategy to control PRRSV infection.

Peptide nanofiber hydrogel adjuvanted live virus vaccine enhances cross-protective immunity to porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is prevalent in swine farms worldwide and is a major source of economic loss and animal suffering. Rapid genetic variation of PRRSV makes it difficult for current vaccines to confer protection against newly emerging strains. We recently demonstrated that a novel peptide nanofiber hydrogel (H9e) could act as a potent adjuvant for killed H1N1 vaccines. Therefore, the objective of this study was to evaluate H9e as an adjuvant for PRRSV modified live virus (MLV) vaccines. Pigs were vaccinated with Ingelvac PRRSV MLV with or without H9e adjuvant before being challenged with the VR-2332 (parental vaccine strain) or MN184A (genetically diverse strain) PRRSV. Pigs vaccinated with MLV+H9e had higher levels of circulating vaccine virus. More importantly, pigs vaccinated with MLV+H9e had improved protection against challenge by both PRRSV strains, as demonstrated by reduced challenge-induced viremia compared with pigs vaccinated with MLV alone. Pigs vaccinated with MLV+H9e had lower frequency of T-regulatory cells and IL-10 production but higher frequency of Th/memory cells and IFN-γ secretion than that in pigs vaccinated with MLV alone. Taken together, our studies suggest that the peptide nanofiber hydrogel H9e, when combined with the PRRSV MLV vaccine, can enhance vaccine efficacy against two different PRRSV strains by modulating both host humoral and cellular immune responses.

Plasmids expressing porcine interferon gamma up-regulate pro-inflammatory cytokine and co-stimulatory molecule expression which are suppressed by porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) suppresses the pro-inflammatory immune response following infection of myeloid antigen-presenting cells. A reduced pro-inflammatory immune response modulates PRRSV replication, clinical disease, and persistent infection of the virus. Numerous efforts have been made to enhance the pro-inflammatory immune response to PRRSV, but only a few attempts have so far elicited satisfactory results. The present study aims to evaluate in vitro the potential of plasmids expressing porcine interferon gamma (pcDNA-IFNγ) to enhance the expression of pro-inflammatory immune parameters in PRRSV-inoculated monocytes. Naïve blood monocytes from eight PRRSV-seronegative pigs were inoculated with PRRSV and subsequently transfected with pcDNA-IFNγ or pcDNA (empty plasmid vector) and stimulated with lipopolysaccharide (LPS). The mRNA expression levels of IFNγ, interleukin-1 beta (IL-1β), IL-10, IL-12p40, tumor necrosis factor alpha (TNFα), transforming growth factor beta (TGFβ), CD80, and CD86 were evaluated by real-time PCR. The IFNγ, IL-10, and TNFα protein production was determined by ELISA. Compared with PRRSV-inoculated monocyte control, transfection with pcDNA-IFNγ, but not pcDNA, significantly enhanced IFNγ, TNFα, CD80, and CD86 mRNA expression, and IFNγ and TNFα protein production. A slight increase in IL-1β and IL-12p40 mRNA expression was also observed. Neither pcDNA-IFNγ nor pcDNA transfection affected IL-10 and TGFβ expression. Our results thus suggest that pcDNA-IFNγ may be an effective immunostimulator for potentiating the pro-inflammatory immune response to PRRSV.