Cytotoxicity effect and transcriptome analysis of PCV3-infected cells revealed potential viral pathogenic mechanisms.

Porcine circovirus type 3 (PCV3) has become an important pathogen in the global swine industry and poses a threat to pig health, but its pathogenic mechanism remains unknown. In this study, we constructed an innovative, linear infectious clone of PCV3 for rescuing the virus, and explored the transcriptome of infected cells to gain insights into its pathogenic mechanisms. Subsequently, an in vivo experiment was conducted to evaluate the pathogenicity of the rescued virus in pig. PCV3 nucleic acid was distributed across various organs, indicating systemic circulation via the bloodstream and viremia. Immunohistochemical staining also revealed a significant presence of PCV3 antigens in the spleen, lungs, and lymph nodes, indicating that PCV3 had tropism for these organs. Transcriptome analysis of infected ST cells revealed differential expression of genes associated with apoptosis, immune responses, and cellular metabolism. Notably, upregulation of genes related to the hypoxia-inducible factor-1 pathway, glycolysis, and the AGE/RAGE pathway suggests activation of inflammatory responses, ultimately leading to onset of disease. These findings have expanded our understanding of PCV3 pathogenesis, and the interplay between PCV3 and host factors.

Enhancing expression of the classical swine fever virus glycoprotein E2 in yeast and its application to a blocking ELISA.

Classical swine fever virus (CSFV) infection is a severe swine disease, often causing large economic losses. A Pichia pastoris yeast-expressed CSFV glycoprotein E2 (yE2) has been shown to induce a protective immune response against the virus. To improve the expression level of yE2, the first codon of E2 gene, Arg (CGG), which is the least used in P. pastoris, was optimized to the most favorite codon AGA. The yield of E2 protein was remarkably increased in the codon optimized strain (N342). Three truncated E2 subunits encoding the N-terminal 330 (N330), 301 (N301), and 190 (N190) residues, respectively, were also constructed. The immunogenicity of each recombinant E2 subunits was confirmed by immunization of pigs, and all immunized groups demonstrated high neutralizing antibody titers after boost immunization, which lasted for a long period of time. In addition, a monoclonal antibody (MAb), 1B6, specific to yE2, was generated and shown to recognize CSFV-infected cells. A panel of swine sera were tested by peroxidase-conjugated MAb 1B6-based blocking enzyme-linked immunosorbent assay (ELISA) using N330 as coated antigen, and the assay demonstrated high sensitivity and specificity. The recombinant yE2 subunits may provide potential subunit vaccine candidates and useful diagnostic reagents for CSFV with easy manipulation and low cost.

Yeast expressed classical swine fever E2 subunit vaccine candidate provides complete protection against lethal challenge infection and prevents horizontal virus transmission.

Classical swine fever (CSF) caused by the classical swine fever virus (CSFV) is a highly contagious swine disease resulting in large economical losses worldwide. The viral envelope glycoprotein E(rns) and E2 are major targets for eliciting antibodies against CSFV in infected animals. A Pichia pastoris yeast expressed E2 protein (yE2) has been shown to induce a protective immune response against CSFV challenge. The purpose of this study is to determine the optimal dose of yE2 and its efficacy on the prevention of virus horizontal transmission. A yeast-expressed E(rns) (yE(rns)) protein was also included to evaluate its immunogenicity. The yE(rns) vaccinated pigs seroconverted to CSFV-E(rns)-specific antibody but no neutralizing antibody was detected and none survived after challenge infection, suggesting yE(rns) and yE2 retain correct immunogenicity but only the yE2 is able to induce a protective immune response. All three doses of yE2 (200, 300, and 400µg) could elicit high titers of neutralizing antibodies and protective responses after challenge. The yE2/200 group demonstrated a mild fever response but recovered soon, and none of the yE2/300 and yE2/400 pigs became febrile. The optimal dose of yE2 was recommended to be 300µg of the total amount of secreted proteins. In addition, the yE2 vaccine could cross-protect from all three genotypes of viruses. Further, the yE2 vaccine efficacy in preventing virus horizontal transmission was evaluated by cohabitation of unimmunized sentinels 3 days after challenge infection. All the sentinel pigs were alive and had no clinical symptoms confirming yE2 vaccine could confer a protective immune response and prevent horizontal transmission of CSFV.

Characterization of the monoclonal antibody against classical swine fever virus glycoprotein E(rns) and its application to an indirect sandwich ELISA.

Classical swine fever virus (CSFV) E(rns) is an envelope glycoprotein possessing RNase activity. The E(rns)-based enzyme-linked immunosorbent assay (ELISA) has been considered a discriminating diagnostic test for differentiating infected from vaccinated animals. The purpose of this study was to produce a specific monoclonal antibody (MAb) to E(rns) for further developing an indirect sandwich ELISA. The MAb CW813 was shown to specifically recognize both the monomer and dimer forms of Pichia pastoris yeast-expressed E(rns) (yE(rns)). The antigenic site recognized by MAb CW813 was mapped to the region of amino acid residues 101-160 of E(rns) where it was neither a neutralizing epitope nor essential to RNase activity. Furthermore, MAb CW813 was utilized as a capture antibody to develop a yE(rns)-based indirect sandwich ELISA for detecting swine antibody to E(rns). The assay demonstrated a high sensitivity and specificity that may provide an alternative method for developing a diagnostic kit with easy manipulation and low cost.

Yeast-expressed classical swine fever virus glycoprotein E2 induces a protective immune response.

Classical swine fever (CSF) is an economically important swine disease worldwide. The glycoprotein E2 of classical swine fever virus (CSFV) is a viral antigen that can induce a protective immune response against CSF. A recombinant E2 protein was constructed using the yeast Pichia pastoris expression system and evaluated for its vaccine efficacy. The yeast-expressed E2 (yE2) was shown to have N-linked glycosylation and to form homodimer molecules. Four 6-week-old specified-pathogen-free (SPF) piglets were intramuscularly immunized with yE2 twice at 3-week intervals. All yE2-vaccinated pigs could mount an anamnestic response after booster vaccination with neutralizing antibody titers ranging from 1:96 to 1:768. Neutralizing antibody titers at 10 weeks post booster vaccination ranged from 1:16 to 1:64. At this time, the pigs were subjected to challenge infection with a dose of 1x10(5)TCID(50) (50% tissue culture infective dose) virulent CSFV strain. At 1 week post challenge infection, all of the yE2-immunized pigs were alive and without symptoms or signs of CSF. Neutralizing antibody titers at this time ranged from 1:4,800 to 1:12,800 and even to 1:51,200 one week later. In contrast, the control pigs continuously exhibited signs of CSF and had to be euthanized because of severe clinical symptoms at 6 days post challenge infection. All of the yE2-vaccinated pigs were E(rns) antibody negative and had seroconverted against E(rns) by post challenge day 11, suggesting that yE2 is a potential DIVA (differentiating infected from vaccinated animals) vaccine. The yeast-expressed E2 protein retains correct immunogenicity and is able to induce a protective immune response against CSFV infection.