ORF1a of highly pathogenic PRRS attenuated vaccine virus plays a key role in neutralizing antibody induction in piglets and virus neutralization in vitro

Epidemiological investigation and pathogenicity of porcine reproductive and respiratory syndrome virus in Sichuan, China

Porcine reproductive and respiratory syndrome virus type 2 (PRRSV-2) lineage 8 was first detected in mainland China in 2006 and has since rapidly spread to become the primary epidemic strain in the country. In this study, samples such as lung tissue, hilar lymph nodes, abortion fetuses, and blood were collected from large-scale pig farms across 11 prefecture-level cities in Sichuan province between 2019 and 2020 for antigen detection and PRRS virus isolation. The antigen detection results indicated that the positive rate of HP-PRRSV (JXA1-Like strain) was 44.74% (51/114), NADC30-Like PRRSV was 17.54% (20/114), and classical PRRSV (VR2332-Like strain) was 37.72% (43/114). The predominant strain was HP-PRRSV. Positive samples were further inoculated into Marc-145 cells for virus isolation and identification, leading to the isolation of a new JXA1-Like PRRSV strain named SCSN2020. The strain was characterized by RT-qPCR, indirect immunofluorescence assay (IFA), plaque purification, electron microscopy, and whole genome sequencing. The total length of the viral genome was determined to be approximately 15,374 bp. A comparison of the SCSN2020 genome with VR2332 revealed that both strains had the same discontinuous 30-amino acid deletion on the Nsp2 gene. ORF5 genotyping classified the SCSN2020 strain as sublineage 8.7, with a whole genome sequence identity of 99.34% with JXA1. Furthermore, we evaluated the pathogenicity of the SCSN2020 strain in 28-day-old piglets and observed persistent fever from day 4 to day 10, weight loss started on day 7, dyspnea and severe lung lesions began started on day 14. The results of this study highlight the current PRRSV epidemic situation in Sichuan province and provide a scientific reference for subsequent prevention and control measures.

Lineage 1 Porcine Reproductive and Respiratory Syndrome Virus Attenuated Live Vaccine Provides Broad Cross-Protection against Homologous and Heterologous NADC30-Like Virus Challenge in Piglets

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen that endangers the swine industry worldwide. Recently, lineage 1 PRRSVs, especially NADC30-like PRRSVs, have become the major endemic strains in many pig-breeding countries. Since 2016, NADC30-like PRRSV has become the predominant strain in China. Unfortunately, current commercial vaccines cannot provide sufficient protection against this strain. Here, an attenuated lineage 1 PRRSV strain, named SD-R, was obtained by passaging an NADC30-like PRRSV strain SD in Marc-145 cells for 125 passages. Four-week-old PRRSV-free piglets were vaccinated intramuscularly with 105.0TCID50 SD-R and then challenged intramuscularly (2 mL) and intranasally (2 mL) with homologous NADC30-like PRRSV SD (1 × 105.0TCID50/mL) and heterologous NADC30-like PRRSV HLJWK108-1711 (1 × 105.0TCID50/mL). The results showed that antibodies against specific PRRSVs in 5 of 5 immunized piglets were positive after a 14-day post-vaccination and did not develop fever or clinical diseases after NADC30-like PRRSV challenges. Additionally, compared with challenge control piglets, vaccinated piglets gained significantly more weight and showed much milder pathological lesions. Furthermore, the viral replication levels of the immunized group were significantly lower than those of the challenge control group. These results demonstrate that lineage 1 PRRSV SD-R is a good candidate for an efficacious vaccine, providing complete clinical protection for piglets against NADC30-like PRRSVs.

Minor and major envelope proteins of PRRSV play synergistic roles in inducing heterologous neutralizing antibodies and conferring cross protection

High genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV) isolates is a major obstacle for the development of effective PRRS vaccines. A chimeric highly pathogenic PRRSV2 (HP-PRRSV2) strain containing the consensus sequence of ORF2-6 genes was constructed in our previous study, which could induce broadly neutralizing antibodies (bnAbs) and confer satisfied cross protection against virulent NADC30-like isolate. To further elucidate the roles of minor and major envelope proteins encoded by ORF2-4 and ORF5-6 genes in conferring cross protection, two chimeric HP-PRRSV2 strains (rJS-ORF2-4-CON and rJS-ORF5-6-CON) containing consensus sequences of ORF2-4 or ORF5-6 were constructed and rescued in this study. The rJS-ORF5-6-CON strain has similar replication efficiency as the backbone HP-PRRSV2 rJSTZ1712-12 virus, while rJS-ORF2-4-CON has significantly lower in vitro and in vivo replication efficiency comparing to rJS-ORF5-6-CON. Animal inoculation indicated that both rJS-ORF2-4-CON and rJS-ORF5-6-CON did not cause obvious clinical signs in piglets and could induce heterologous nAbs after immunization. Challenge with a virulent heterologous NADC30-like SD17-38 isolate showed that even though both immunized groups presented lower viremia, faster virus elimination, less fever and alleviated lung gross lesions when compared with the only challenged pigs, rJS-ORF2-4-CON and rJS-ORF5-6-CON could not confer enough cross protection. Considering the bnAbs and satisfied cross protection induced by the chimeric virus containing ORF2-6 consensus sequence, our results support that minor and major envelope proteins play synergistic roles in inducing broader nAbs and conferring better cross protection.

The Antiviral Effect of Isatis Root Polysaccharide against NADC30-like PRRSV by Transcriptome and Proteome Analysis

(1) Background: In recent years, the porcine reproductive and respiratory syndrome virus (PRRSV) has become a virulent pathogen that has caused devastating diseases and economic losses worldwide in the swine industry. IRPS has attracted extensive attention in the field of virology. However, it is not clear that IRPS has an antiviral effect on PRRSV at gene and protein levels. (2) Methods: We used transcriptomic and proteomic analysis to investigate the antiviral effect of IRPS against PRRSV. Additionally, a microbiome was used to explore the effects of IRPS on gut microbes. (3) Results: IRPS significantly extenuated the pulmonary pathological lesions and inflammatory response. We used transcriptomic and proteomic analysis to investigate the antiviral effect of IRPS against PRRSV. In the porcine model, 1669 differentially expressed genes (DEGs) and 370 differentially expressed proteins (DEPs) were identified. Analysis of the DEG/DEP-related pathways indicated immune-system and infectious-disease (viral) pathways, such as the NOD-like receptor (NLR) signaling pathway, toll-like receptor (TLR) signaling pathway, and Influenza A-associated signaling pathways. It is noteworthy that IRPS can inhibit NLR-dependent gene expression, then reduce the inflammatory damage. IRPS could exert beneficial effects on the host by regulating the structure of intestinal flora. (4) Conclusions: The antiviral effect of IRPS on PRRSV can be directly achieved by omics techniques. Specifically, the antiviral mechanism of IPRS can be better elucidated by screening target genes and proteins using transcriptome and proteome sequencing, and then performing enrichment and classification according to DEGs and DEPs.

Immunogenic and antigenic analysis of recombinant NSP1 and NSP11 of PRRS virus

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) is an enveloped RNA virus in the order Nidovirales, family Arteriviridae, genus Betaarterivirus. Antibodies against nonstructural proteins (NSPs) from this virus can be found in pigs starting 4 days postinfection and they remain detectable for several months.

Objective

The goal of this study was to evaluate the immunogenicity and antigenic properties of recombinant proteins NSP1 and NSP11 expressed in Escherichia coli cells, as well as to assess the neutralization activity that they elicit.

Methods

We obtained the complete ORF‐1 genes coding for NSP1 and NSP11 from PRRSV using the VR‐2332 strain. Cloning was performed with the pET23a(+) vector with a histidine tag (His6), linearized by restriction enzyme digestion; the expression of the NSP1 and NSP11 clones was induced in OverExpress C41(DE3) chemically competent cells. Recombinant proteins were used to generate hyperimmune sera and we perform serological assays to confirm neutralizing antibodies.

Results

The expressed recombinant NSP1 and NSP11 were found to be immunogenic when injected in pigs, as well as demonstrated higher specificity in recognition of antigen in field sera from pigs positive infected with PRRSV. Furthermore, both NSP1 and NSP11 recombinant proteins elicited PRRSV neutralizing antibodies.

Conclusions

In this study, we demonstrated the immune humoral response to NSP 1 and NSP11, and neutralizing‐antibody response to PRRSV VR2332 strain in sera from hyperimmunized pigs.

Porcine Reproductive and Respiratory Syndrome Virus: Immune Escape and Application of Reverse Genetics in Attenuated Live Vaccine Development

Porcine reproductive and respiratory syndrome virus (PRRSV), an RNA virus widely prevalent in pigs, results in significant economic losses worldwide. PRRSV can escape from the host immune response in several processes. Vaccines, including modified live vaccines and inactivated vaccines, are the best available countermeasures against PRRSV infection. However, challenges still exist as the vaccines are not able to induce broad protection. The reason lies in several facts, mainly the variability of PRRSV and the complexity of the interaction between PRRSV and host immune responses, and overcoming these obstacles will require more exploration. Many novel strategies have been proposed to construct more effective vaccines against this evolving and smart virus. In this review, we will describe the mechanisms of how PRRSV induces weak and delayed immune responses, the current vaccines of PRRSV, and the strategies to develop modified live vaccines using reverse genetics systems.

Immunity against a Japanese local strain of porcine reproductive and respiratory syndrome virus decreases viremia and symptoms of a highly pathogenic strain

Background

The type 2 highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) has spread throughout countries of southeast Asia, where it has caused severe economic losses. Even countries presently free of PRRSV are at high risk for infection and spread of this virus. Some of these countries, including Japan, have broad epidemics of the local type 2 PRRSV, creating chronic pathogenicity in the domestic pig population. The present study aimed to evaluate the protective efficacy of immunity by infection with a Japanese field isolate, EDRD1, against heterologous challenge with a Vietnamese HP-PRRSV field strain. To this end, four groups of PRRSV-negative crossbreed piglets were used for a challenge study. Groups 1 and 2 were inoculated with EDRD1 via the intranasal route. After 26 days, Groups 2 and 3 were inoculated with HP-PRRSV via the same route. Group 4 served as an uninfected control. Blood and oral fluid samples were taken every 3–4 days after HP-PRRSV challenge; on day 16 post-challenge, all pigs were euthanized, and examined pathologically.

Results

The nucleotide sequence analysis of nonstructural protein 2 gene of EDRD1 and comparison with Vietnamese HP-PRRSV showed that the 39 amino acid deletion sites of EDRD1 was nearly in the same region as the 29 amino acid deletion sites of HP-PRRSV. Immunity conferred by inoculation with EDRD1 dramatically reduced viral load in the sera and tissues besides viral shedding (Group 2) compared with those in pigs infected only with HP-PRRSV (Group 3). The clinical signs and rectal temperature were significantly reduced, and the average daily weight gain was significantly improved in the EDRD1-inoculated pigs (Group 2) compared with the Group 3 pigs. Notably, no viral RNA was detected in various organs of the Group 2 pigs 16 days post-infection with HP-PRRSV, except in one pig. Therefore, the immunity induced by EDRD1 and its genetically close field isolates may play a role in reducing viremia caused by HP-PRRSV.

Conclusions

The results of the present study demonstrate that pigs are highly protected against heterologous Vietnamese HP-PRRSV challenge by immunity against a Japanese local strain, EDRD1.

Intradermal co-inoculation of codon pair deoptimization (CPD)-attenuated chimeric porcine reproductive and respiratory syndrome virus (PRRSV) with Toll like receptor (TLR) agonists enhanced the protective effects in pigs against heterologous challenge

The objective of this study was to assess protective efficacy of vaccination using CPD-attenuated chimeric PRRSV and Toll like receptor (TLR) agonists (HSP70 c-terminal domain and HSPX) as adjuvants through different inoculation routes. In this study, a chimeric PRRSV composed of two field isolates was synthesized and attenuated by CPD in NSP1 as described in the previous study. The infection of the CPD-attenuated chimeric PRRSV to pigs of 3 weeks-old showed no clinical signs without pathological lesions in necropsy, while it induced improved cross immunity between its parent strains. The TLR agonists were expressed in E. coli and purified to be used. In challenge experiment, pigs of 3 weeks-old were vaccinated using the CPD-attenuated chimeric virus with the prepared TLR agonists through intramuscular or intradermal route, following heterologous challenge after 4 weeks of vaccination. In results, intramuscular or intradermal inoculation of the CPD-attenuated chimeric virus demonstrated excellent protective efficacy against heterologous challenges. Importantly, intradermal inoculation with the TLR agonists enhanced protective effects as shown in the significantly increased level of PRRSV-specific IFN-γ-SCs and cytokines in sera, and the significant reduction of pathological lesion and viral load in lung. This study suggested that the intradermal inoculation of CPD-attenuated chimeric PRRSV plus TLR agonists should be more effective for protection of pigs against diverse PRRS field viruses.

Nsp2 and GP5-M of Porcine Reproductive and Respiratory Syndrome Virus Contribute to Targets for Neutralizing Antibodies

Porcine reproductive and respiratory syndrome virus (PRRSV) is characterized by its genetic variation and limited cross protection among heterologous strains. Even though several viral structural proteins have been regarded as inducers of neutralizing antibodies (NAs) against PRRSV, the mechanism underlying limited cross-neutralization among heterologous strains is still controversial. In the present study, examinations of NA cross reaction between a highly pathogenic PRRSV (HP-PRRSV) strain, JXwn06, and a low pathogenic PRRSV (LP-PRRSV) strain, HB-1/3.9, were conducted with viral neutralization assays in MARC-145 cells. None of the JXwn06-hyperimmuned pigs' sera could neutralize HB-1/3.9 in vitro and vice versa. To address the genetic variation between these two viruses that are associated with limited cross-neutralization, chimeric viruses with coding regions swapped between these two strains were constructed. Viral neutralization assays indicated that variations in nonstructural protein 2 (nsp2) and structural proteins together contribute to weak cross-neutralization activity between JXwn06 and HB-1/3.9. Furthermore, we substituted the nsp2-, glycoprotein2 (GP2)-, GP3-, and GP4-coding regions together, or nsp2-, GP5-, and membrane (M) protein-coding regions simultaneously between these two viruses to construct chimeric viruses to test cross-neutralization reactivity with hyperimmunized sera induced by their parental viruses. The results indicated that the swapped nsp2 and GP5-M viruses increased the neutralization reactivity with the donor strain antisera in MARC-145 cells. Taken together, these results show that variations in nsp2 and GP5-M correlate with the limited neutralization reactivity between the heterologous strains HP-PRRSV JXwn06 and LP-PRRSV HB-1/3.9.

Targeted-pig trial on safety and immunogenicity of serum-derived extracellular vesicles enriched fractions obtained from Porcine Respiratory and Reproductive virus infections

The Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is the etiological agent of one of the most important swine diseases with a significant economic burden worldwide. Unfortunately, available vaccines are partially effective highlighting the need of novel approaches. Previously, antigenic viral proteins were described in serum-derived extracellular vesicles (EVs) from pigs previously infected with PRRSV. Here, a targeted-pig trial was designed to determine the safety and immunogenicity of such extracellular vesicles enriched fractions. Our results showed that immunizations with EV-enriched fractions from convalescence animals in combination with montanide is safe and free of virus as immunizations with up-to two milligrams of EV-enriched fractions did not induce clinical symptoms, adverse effects and detectable viral replication. In addition, this vaccine formulation was able to elicit specific humoral IgG immune response in vaccinated animals, albeit variably. Noticeably, sera from vaccinated animals was diagnosed negative when tested for PRRSV using a commercial ELISA test; thus, indicating that this new approach differentiates vaccinated from infected animals. Lastly, after priming animals with EV-enriched fractions from sera of convalescence animals and boosting them with synthetic viral peptides identified by mass spectrometry, a distinctive high and specific IFN-γ response was elicited. Altogether, our data strongly suggest the use of serum EV-enriched fractions as a novel vaccine strategy against PRRSV.

Adaptions of field PRRSVs in Marc-145 cells were determined by variations in the minor envelope proteins GP2a-GP3

The recent rapid evolution of PRRSVs has resulted in certain biological characteristic changes, such as the fact that an increasing number of field PRRSVs can be isolated from PAMs but not from Marc-145 cells. In this study, we first isolated Marc-145-unadaptive field PRRSV strains from PAMs; sequence analysis showed that these PRRSVs belong to the HP-PRRSV (lineage 8) branch or NADC30-Like (lineage 1) branch. We further found major variations in ORF2-4 regions. To explore the viral adaptation mechanisms in detail, we constructed a full-length cDNA clone of MY-376, a Marc-145-unadaptive PRRSV. Construction of serially chimeric viruses of HuN4-F112 (a Marc-145-adaptive strain) and MY-376 demonstrated that variation in the minor envelope protein (GP2a and GP3) complex is a main determinant of PRRSV tropism for Marc-145 cells.