Efficacy of a live attenuated highly pathogenic PRRSV vaccine against a NADC30-like strain challenge: implications for ADE of PRRSV

Background Porcine reproductive and respiratory syndrome virus (PRRSV) infection can cause severe reproductive failure in sows and respiratory distress in pigs of all ages, leading to major economic losses. To date, there are still no effective strategies to prevent and control PRRSV. Antibody-dependent enhancement (ADE), a phenomenon in which preexisting non-neutralizing antibodies or sub-neutralizing antibodies facilitate virus entry and replication, may be a significant obstacle in the development of effective vaccines for many viruses, including PRRSV. However, the contribution of ADE to PRRSV infection remains controversial, especially in vivo. Whether attenuated PRRSV vaccines prevent or worsen subsequent disease in pigs infected by novel PRRSV strains requires more research. In the present study, in vivo experiments were conducted to evaluate ADE under different immune statuses, which were produced by waiting different lengths of time after vaccination with a commercially available attenuated highly pathogenic PRRSV (HP-PRRSV) vaccine (JXA1-R) before challenging the pigs with a novel heterologous NADC30-like strain. Results Piglets that were vaccinated before being challenged with PRRSV exhibited lower mortality rates, lower body temperatures, higher bodyweight gain, and lower viremia. These results demonstrate that vaccination with JXA1-R alleviated the clinical signs of PRRSV infection in all vaccinated groups. Conclusions The obtained data indicate that the attenuated vaccine test here provided partial protection against the NADC30-like strain HNhx. No signs of enhanced PRRSV infection were observed under the applied experimental conditions. Our results provide some insight into the molecular mechanisms underlying vaccine-induced protection or enhancement in PRRSV.

Porcine Reproductive and Respiratory Syndrome Virus Structural Protein GP3 Regulates Claudin 4 To Facilitate the Early Stages of Infection

ABSTRACT Claudins (CLDN) are a family of proteins that represent the most important components of tight junctions, where they establish the paracellular barrier that controls the flow of molecules in the intercellular space between epithelial cells. Several types of viruses make full use of CLDN to facilitate entry into cells. Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important pathogens in the swine industry. In this study, we found that CLDN4 functions as an anti-PRRSV factor by blocking its absorption during the early stages of infection. The small extracellular loop (ECL2) of CLDN4 restricted the viral particles outside cells by binding to GP3. A novel function of GP3-mediated regulation of CLDN4 transcription was suggested. CLDN4 can be decreased through downregulating the level of CLDN4 transcription by ubiquitinating the transcription factor, SP1. The mechanism by which highly pathogenic PRRSV infects the epithelium was proposed. Importantly, ECL2 was found to block PRRSV absorption and infection and neutralize the virus. A more in-depth understanding of PRRSV infection is described, and novel therapeutic antiviral strategies are discussed. IMPORTANCE In the present study, the role of CLDN4 in PRRSV infection was studied. The results showed that CLDN4 blocked absorption into cells and restricted extracellular viral particles via the interaction between the CLDN4 small extracellular loop, ECL2, and the viral surface protein GP3. GP3 was found to downregulate CLDN4 through ubiquitination of the transcription factor SP1 to facilitate viral entry. The mechanism by which highly pathogenic PRRSV infects the epithelium is suggested. A novel function of GP3 in regulating gene transcription was discovered. Moreover, ECL2 could block PRRSV absorption and infection, as well as neutralizing the virus in the supernatant, which may lead to the development of novel therapeutic antiviral strategies.

Cellular microRNA miR-c89 inhibits replication of porcine reproductive and respiratory syndrome virus by targeting the host factor porcine retinoid X receptor β

MicroRNAs (miRNAs) play critical roles in the complex networks of virus–host interactions. Our previous research showed that porcine reproductive and respiratory syndrome virus (PRRSV) infection markedly upregulates miR-c89 expression, suggesting that miR-c89 may play an important role in PRRSV infection. The present study sought to determine the function of miR-c89 and its molecular mechanism during PRRSV infection. Using quantitative reverse transcription PCR (RT-qPCR) verification, we demonstrated that both highly pathogenic PRRSV and low-pathogenic PRRSV infection induced miR-c89 expression. The overexpression of miR-c89 significantly suppressed the replication of a variety of PRRSV strains, regardless of the timing of infection. Further, miR-c89 can directly target the 3′UTR of porcine retinoid X receptor β (RXRB) mRNA in a sequence-specific manner. Knockdown affected RXRB expression, as siRNA can suppress the replication of a variety of PRRSV strains. This work not only provides new insights into PRRSV–cell interactions, but also highlights the potential for the use of miR-c89 in the development of new antiviral strategies to combat PRRSV infection.

Complete Genome Sequence of a Recombinant NADC30-Like Strain, SCnj16, of Porcine Reproductive and Respiratory Syndrome Virus in Southwestern China

ABSTRACTThe NADC30-like strains of porcine reproductive and respiratory syndrome virus (PRRSV) are characterized by a 131-amino-acid deletion in nonstructural protein 2 (NSP2). Here, we report the complete genome sequence of a recombinant NADC30-like PRRSV strain, SCnj16, that exhibits the molecular marker of the Chinese highly pathogenic PRRSV (HP-PRRSV) in NSP2.

Development and Application of an RT-PCR to Differentiate the Prevalent NA-PRRSV Strains in China

Background: PRRSV features with genetic diversity and high mutation which leads to the emergence of a multiple of circulating virus strains with different virulence. North American (genotype 2) PRRSV (NA-PRRSV) can be divided into classical PRRSV (C-PRRSV), highly pathogenic PRRSV (HP-PRRSV), and NADC30-like PRRSV (NL-PRRSV) according to their genomic characteristics and pathogenicity. So far, the above three subtypes of NA-PRRSV are now circulating in China. Objective and Method: In this study, a reverse transcript polymerase chain reaction (RT-PCR) was established to simultaneously differentiate three subtypes of NA-PRRSV. The established RT-PCR can be applied to PRRSV-infected samples originated from both supernatant of cell culture and pig tissues and showed specificity exclusively to PRRSV. The sensitivity of RT-PCR showed the minimum RNA detection was 0.04ng/µl. Result and Conclusion: The established RT-PCR was next used to differentiate the subtypes of 29 NA-PRRSV isolated in 2016 and the results showed that HP-PRRSV is still the dominant circulating virus strain in the presence of NADC30-like PRRSV in Henan province.

NADC30-Like Porcine Reproductive and Respiratory Syndrome in China

NADC30-like porcine reproductive and respiratory syndrome virus (PRRSV) has widely spread in China and become locally dominant virus strain in some provinces. Although they are not pathogenic as highly pathogenic PRRSV (HP-RRRSV) that outbreaks since 2006, NADC30-like PRRSVs distinguished themselves by high incidence of recombination with other virus strains which lead to change of virulence. The outbreaks of NADC30-like PRRSV in the vaccinated pig herds suggested that current commercial PRRSV vaccines cannot provide complete protection to the infection. In this review, we have described in detail the current situation of NADC30 PRRSV including epidemiology, genomic characterization, pathogenicity, and efficacy of current commercial vaccines in China.