Antigenic analysis of classical swine fever virus E2 glycoprotein using pig antibodies identifies residues contributing to antigenic variation of the vaccine C-strain and group 2 strains circulating in China

Abstract

BackgroundGlycoprotein E2, the immunodominant protein of classical swine fever virus (CSFV), can induce neutralizing antibodies and confer protective immunity in pigs. Our previous phylogenetic analysis showed that subgroup 2.1 viruses branched away from subgroup 1.1, the vaccine C-strain lineage, and became dominant in China. The E2 glycoproteins of CSFV C-strain and recent subgroup 2.1 field isolates are genetically different. However, it has not been clearly demonstrated how this diversity affects antigenicity of the protein.ResultsAntigenic variation of glycoprotein E2 was observed not only between CSFV vaccine C-strain and subgroup 2.1 strains, but also among strains of the same subgroup 2.1 as determined by ELISA-based binding assay using pig antisera to the C-strain and a representative subgroup 2.1 strain QZ-07 currently circulating in China. Antigenic incompatibility of E2 proteins markedly reduced neutralization efficiency against heterologous strains. Single amino acid substitutions of D705N, L709P, G713E, N723S, and S779A on C-strain recombinant E2 (rE2) proteins significantly increased heterologous binding to anti-QZ-07 serum, suggesting that these residues may be responsible for the antigenic variation between the C-strain and subgroup 2.1 strains. Notably, a G713E substitution caused the most dramatic enhancement of binding of the variant C-strain rE2 protein to anti-QZ-07 serum. Multiple sequence alignment revealed that the glutamic acid residue at this position is conserved within group 2 strains, while the glycine residue is invariant among the vaccine strains, highlighting the role of the residue at this position as a major determinant of antigenic variation of E2. A variant Simpson's index analysis showed that both codons and amino acids of the residues contributing to antigenic variation have undergone similar diversification.ConclusionsThese results demonstrate that CSFV vaccine C-strain and group 2 strains circulating in China differ in the antigenicity of their E2 glycoproteins. Systematic site-directed mutagenesis of the antigenic units has revealed residues that limit cross-reactivity. Our findings may be useful for the development of serological differential assays and improvement of immunogenicity of novel classical swine fever vaccines.

Plant‐made E2 glycoprotein single‐dose vaccine protects pigs against classical swine fever

“…The virus neutralization test (VNT) to determine neutralizing antibody titre in serum samples was carried out as previously described (Chen et al, 2010). Briefly, 50 lL of 100 TCID 50 CSFV Brescia strain were mixed with an equal volume of twofold serially diluted pig sera in a 96-well plate and incubated at 37°C for 1 h before 100 lL of DMEM containing 1 9 10 5 /mL SK6 cell, 10% FBS and 1X antibiotic-antimycotic was added to all wells in 96-well plates.…”

Genetic evolution of classical swine fever virus under immune environments conditioned by genotype 1-based modified live virus vaccine

“…and reports of disease outbreaks by CSFV genotype 1 have been limited to Central and South America (Postel et al., ; Silva et al., ). One suggested reason for a global switch in predominant viral genotype is that all CSFV vaccine strains target genotype 1 (Chen et al., ).…”

Glycoprotein E2 of classical swine fever virus expressed by baculovirus induces the protective immune responses in rabbits

“…The CSFV-2.1E2 vaccine did not produce complete protection, as indicated by the fever exhibited by two rabbits from this group and the presence of viral RNA in the spleen. Previous phylogenetic analysis showed that subgroup 2.1 viruses branched away from subgroup 1.1, the vaccine C-strain lineage [22]. The C-strain is an attenuated virus through repeated passages of virulent strain Shimen in rabbits.…”

“…Commercially available vaccines based on C-strain are effective and provide complete protection against the three groups of CSFV but could not offer differentiability of infected from vaccinated animals [20,21]. The CSFV vaccine C-strain and subgroup 2.1 strains of the glycoprotein E2 have antigenic variations that are primarily determined by an amino acid sequence (702-731 aa) [22]. The commercial CSFV E2 subunit vaccines BAYOVAC ® CSF Marker and Porcilis ® Pesti are derived from genotype 1; these vaccines do not completely protect against the heterologous strain of genotype 2.1, which may be related to antigenic variations among different genotypes [3,21].…”