Highly pathogenic porcine reproductive and respiratory syndrome virus GP5 B antigenic region is not a neutralizing antigenic region.

In 2006, highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) caused great economic losses emerged in China and continues to be a threat for the pig industry. B antigenic region (AR) ((37)SHL/FQLIYNL(45)) of GP5 was considered to be a major linear neutralizing AR in PRRSV classical strains. However, peptide-purified antibodies against this AR did not neutralize PRRSV in a recent report. Compared with classical PRRSV, one amino acid mutation (L/F(39)→ I(39)) was found in B AR of HP-PRRSV. To study the ability of B AR of HP-PRRSV to induce neutralizing antibody (NA) in vitro and in vivo, rabbit antisera against B AR with and without the mutation and pig hyperimmune sera with high titer of NAs against HP-PRRSV were prepared. Immunofluorescence assays (IFA) showed that the two rabbit antisera both had reactivity to classical PRRSV CH-1a and HP-PRRSV HuN4 with no observable difference in IFA titer. However, antisera did not have neutralizing activity against classical PRRSV CH-1a and HP-PRRSV HuN4. No correlation was observed between the levels of anti-B AR peptide antibodies and NAs in pig hyperimmune sera that were detected by indirect ELISA and virus neutralization, respectively. B AR peptide-specific serum antibodies had no neutralizing activity and, GST-B fusion protein could not inhibit neutralization of NAs in pig hyperimmune sera. Based on these findings, we conclude that B AR of HP-PRRSV is not a neutralizing AR of HP-PRRSV GP5.

Isolation of serotype 2 porcine teschovirus in China: evidence of natural recombination.

Porcine teschovirus (PTV), the pathogen of porcine polioencephalomyelitis, is a member of the family Picornaviridae. In this study, a new PTV strain (designated as JF613) was isolated from pigs in China. It was confirmed by the specific CPE on susceptible cells, RT-PCR and nucleotide sequencing. Analysis of its amino acids sequence of complete polyprotein indicated that the isolate belongs to serotype 2. Genetic recombination is a well-known phenomenon for picornavirus which has been demonstrated in many other members of the family, but it remains so far unclear whether recombination occurs in PTV. To detect possible recombination events, 30 sequences of complete coding regions of PTV strains accessible in GenBank were examined. Putative recombinant sequence was identified with the use of SimPlot program. The result showed that the genomic sequence of our isolate exhibited highest similarities with strains of serotypes 2 and 5, respectively, in two crossover regions, suggesting the recombination event in PTV. Then the mosaic structure of viral genome was confirmed by bootscanning and genetic algorithm for recombination detection (GARD). This represents the first PTV-2 isolate in China. Furthermore, our study provided the first evidence of natural recombination in PTV and indicated that homologous recombination may be a driving force in PTV evolution.