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

The role of major and minor structural proteins of porcine reproductive and respiratory syndrome virus in induction of protective immunity

Introduction

Porcine reproductive and respiratory syndrome virus (PRRSV), an economically significant threat to the world pork production, is notoriously known for its heterogeneity, and therefore the current vaccines often fail to provide efficient cross-protection against diverse PRRSV strains.

Methods

By making chimeric viruses using HP-PRRSV-2 lineage 8 (JXwn06) and lineage 1 NADC30-like strains (CHsx1401) as model organisms, the recently results have shown that the viral structural protein-coding region is critical for induction of homologous immunity. In this study, the chimeric viruses were further constructed by exchanging the region coding for the minor (GP2/3/4) or major (GP5/M) structural proteins of JXwn06 on the backbone of CHsx1401 to generate two mutants CHsx1401-GP234JX and CHsx1401-GP5MJX.

Results

The subsequent animal experiment showed that all three chimeras could confer good protective immunity against the lethal challenge by HP-PRRSV strain JXwn06, and the survived pigs had much lower lung lesions, faster viremia clearance, and lower viral tissue load. However, the exchange of SP region as a whole performed better than either GP2/3/4 or GP5/M region alone, as the pigs in the latter groups showed transient fever following challenge and higher viral load in certain tissues, highlighting a synergistic role. Interestingly, as compared to the group CHsx1401-GP234JX, the group CHsx1401-GP5MJX showed excellent viremia clearance, comparable to the SP group.

Discussion

Our results in this report revealed the important role of ORFs2-4 and ORFs5-6 regions in induction of protective immunity and have important implications in understanding viral pathogenesis and further vaccine development.

Genetic variation and recombination analysis of the GP5 gene of the porcine reproductive and respiratory syndrome virus in Thailand

Introduction

Porcine reproductive and respiratory syndrome (PRRS) is a significant threat to the global swine industry, and its prevalence in Thailand spans over two decades.

Methods

To understand the genetic variation and recombination of the PRRS virus (PRRSV) GP5 gene in Thailand, we retrieved 726 GP5 gene sequences from the NCBI database. Phylogenetic trees were constructed using the neighbor-joining (NJ) and maximum likelihood (ML) methods, and recombination analysis was performed.

Results

Homology analysis was conducted on 83 PRRSV-1 and 83 PRRSV-2 strains. Phylogenetic analysis revealed the prevalence of both PRRSV-1 and PRRSV-2 strains in Thailand, with the latter exhibiting wider distribution. PRRSV-1 strains clustered into clades A, D, and H, while PRRSV-2 strains grouped into lineages 1, 5, and sublineage 8.7, further divided into 8.7/HP and 8.7/NA sublineages. Sublineage 8.7/NA strains accounted for a significant proportion of circulating PRRSV-2 strains. Homology analysis showed nucleotide and amino acid similarities ranging from 75.4 to 100.0% and 41.3 to 100.0% for PRRSV-1, and 78.6 to 100.0% and 70.8 to 100.0% for PRRSV-2 strains. Amino acid sequence alignments revealed mutations, insertions, and deletions in PRRSV-1 GP5, and key residue mutations in PRRSV-2 GP5 associated with biological functions. Recombination analysis identified two recombination events within PRRSV-2 sublineage 8.7 strains.

Discussion

These findings confirm the variability of the GP5 protein. This study enhances our understanding of PRRSV prevalence and genetic variation in Thailand, contributing valuable insights for PRRS prevention and control.

A chimeric porcine reproductive and respiratory syndrome virus 1 strain containing synthetic ORF2-6 genes can trigger T follicular helper cell and heterologous neutralizing antibody responses and confer enhanced cross-protection

The prevalence of porcine reproductive and respiratory syndrome virus 1 (PRRSV1) isolates has continued to increase in Chinese swine herds in recent years. However, no effective control strategy is available for PRRSV1 infection in China. In this study, we generated the first infectious cDNA clone (rHLJB1) of a Chinese PRRSV1 isolate and subsequently used it as a backbone to construct an ORF2-6 chimeric virus (ORF2-6-CON). This virus contained a synthesized consensus sequence of the PRRSV1 ORF2-6 gene encoding all the envelope proteins. The ORF2-6 consensus sequence shared > 90% nucleotide similarity with four representative strains (Amervac, BJEU06-1, HKEU16 and NMEU09-1) of PRRSV1 in China. ORF2-6-CON had replication efficacy similar to that of the backbone rHLJB1 virus in primary alveolar macrophages (PAMs) and exhibited cell tropism in Marc-145 cells. Piglet inoculation and challenge studies indicated that ORF2-6-CON is not pathogenic to piglets and can induce enhanced cross-protection against a heterologous SD1291 isolate. Notably, ORF2-6-CON inoculation induced higher levels of heterologous neutralizing antibodies (nAbs) against SD1291 than rHLJB1 inoculation, which was concurrent with a higher percentage of T follicular helper (Tfh) cells in tracheobronchial lymph nodes (TBLNs), providing the first clue that porcine Tfh cells are correlated with heterologous PRRSV nAb responses. The number of SD1291-strain-specific IFNγ-secreting cells was similar in ORF2-6-CON-inoculated and rHLJB1-inoculated pigs. Overall, our findings support that the Marc-145-adapted ORF2-6-CON can trigger Tfh cell and heterologous nAb responses to confer improved cross-protection and may serve as a candidate strain for the development of a cross-protective PRRSV1 vaccine.