Genomic similarity and antibody-dependent enhancement of immune serum potentially affect the protective efficacy of commercial MLV vaccines against NADC30-like PRRSV

Development a high-sensitivity sandwich ELISA for determining antigen content of porcine circovirus type 2 vaccines

Porcine circovirus type 2 (PCV2) is intensely prevalent in global pig farms. The PCV2 vaccine is an important means of preventing and controlling PCV2. The quality control of PCV2 vaccines is predominantly based on detection techniques such as animal testing and neutralizing antibody titration. Measuring the content of effective proteins in vaccines to measure vaccine efficacy is an excellent alternative to traditional methods, which can greatly accelerate the development speed and testing time of vaccines. In this study, we screened a monoclonal antibody (mAb) that can effectively recognize not only the exogenous expression of PCV2 Cap protein but also PCV2 virus. The double antibody sandwich ELISA (DAS-ELISA) was developed using this mAb that specifically recognize PCV2 Cap. The minimum protein content detected by this method is 3.5 ng/mL. This method can be used for the quality control of PCV2 inactivated vaccine and subunit vaccine, and the detection results are consistent with the results of mice animal experiments. This method has the advantages of simple operation, good sensitivity, high specificity and wide application. It can detect the effective antigen Cap protein content of various types of PCV2 vaccines, which not only shorten the vaccine inspection time but also save costs.

PRRSV degrades MDA5 via dual autophagy receptors P62 and CCT2 to evade antiviral innate immunity

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major economically devastating pathogen that has evolved various strategies to evade innate immunity. Downregulation of antiviral interferon largely promotes PRRSV immunoevasion by utilizing cytoplasmic melanoma differentiation-associated gene 5 (MDA5), a receptor that senses viral RNA. In this study, the downregulated transcription and expression levels of porcine MDA5 in PRRSV infection were observed, and the detailed mechanisms were explored. We found that the interaction between P62 and MDA5 is enhanced due to two factors: the phosphorylation modification of the autophagic receptor P62 by the upregulated kinase CK2α and the K63 ubiquitination of porcine MDA5 catalyzed by the E3 ubiquitinase TRIM21 in PRRSV-infected cells. As a result of these modifications, the classic P62-mediated autophagy is triggered. Additionally, porcine MDA5 interacts with the chaperonin containing TCP1 subunit 2 (CCT2), which is enhanced by PRRSV nsp3. This interaction promotes the aggregate formation and autophagic clearance of MDA5-CCT2-nsp3 independently of ubiquitination. In summary, enhanced MDA5 degradation occurs in PRRSV infection via two autophagic pathways: the binding of MDA5 with the autophagy receptor P62 and the aggrephagy receptor CCT2, leading to intense innate immune suppression. The research reveals a novel mechanism of immune evasion in PRRSV infection and provides fundamental insights for the development of new vaccines or therapeutic strategies.

Natural compound Sanggenon C inhibits porcine reproductive and respiratory syndrome virus replication in piglets

Porcine reproductive and respiratory syndrome virus is one of the main pathogens threatening the global pig industry, and there is still a lack of effective therapeutic drugs. Sanggenon C is a flavanone Diels-Alder adduct compound extracted from the root bark of the mulberry genus, which has blood pressure-reducing, anti-atherosclerotic, anti-oxidative, and anti-inflammatory effects. In our previous study, Sanggenon C was confirmed to significantly inhibit PRRSV replication in vitro. However, its antiviral potential to inhibit PRRSV infection in vivo has not been evaluated in piglets. Here, the antiviral effect of Sanggenon C was evaluated in PRRSV-challenged piglets based on assessments of rectal temperature, viral load, pathological changes of lung tissue and secretion of inflammatory cytokines. The results showed that Sanggenon C treatment relieved the clinical symptoms, reduced the viral loads in the lungs and bloods, alleviated the pathological damage of lung tissue, decreased the secretion of inflammatory cytokines, and shorten the excretion time of virus from the oral and nasal secretions and feces of piglets after PRRSV infection. The results indicated that Sanggenon C is a promising anti-PRRSV drug, which provides a new strategy for the prevention and control of PRRS in clinical practice.