Assessment of the cell-mediated immunity induced by alphavirus replicon-vectored DNA vaccines against classical swine fever in a mouse model.

We have previously shown that an alphavirus replicon-vectored DNA vaccine (pSFV1CS-E2) encoding the E2 glycoprotein of classical swine fever virus (CSFV) completely protected the immunized pigs from lethal challenge. These animals developed only low or moderate level viral-specific antibody titers before challenge, implying that cell-mediated immunity (CMI) probably played an important role in the protective immunity against CSFV conferred by the DNA vaccine. In this study, the CMI induced by pSFV1CS-E2 and its derivative pSFV1CS-E2-UL49 encoding a fusion protein of CSFV E2 and pseudorabies virus (PRV) VP22 was evaluated in a mouse model by lymphoproliferation assays based on CFSE or WST-8, intracellular cytokine staining, and cytokine ELISA. The results showed that both vaccines induced CSFV-specific lymphoproliferative responses and cytokine production, and pSFV1CS-E2-UL49 induced stronger lymphoproliferative responses and higher cytokine levels than pSFV1CS-E2. These findings suggest that the alphavirus replicon-delivered DNA vaccines are capable of inducing CMI, and PRV VP22 is able to enhance the immunogenicity of the co-delivered antigen.

Identification of a conserved linear B-cell epitope at the N-terminus of the E2 glycoprotein of Classical swine fever virus by phage-displayed random peptide library.

The E2 protein of Classical swine fever virus (CSFV) is an important envelope glycoprotein, which is responsible for inducing protective immune response in swine. Four antigenic domains, A-D, have been mapped on the E2 protein. The present study describes the identification of a linear B-cell epitope at the N-terminus of the E2 protein by screening a phage-displayed random 12-peptide library with the neutralizing monoclonal antibody (mAb) HQ06 directed against the E2 protein. HQ06 was found to bind to the phages displaying a consensus motif LFDGSNP, which is highly homologous to (772)LFDGTNP(778) of the CSFV polyprotein, locating on the border between antigenic domains B/C and A of the E2 protein. Considering that HQ06 showed reactivity with the motif (772)LFDGTNP(778) expressed as GST fusion in Western blot and indirect ELISA, we propose that the motif (772)LFDGTNP(778) represents a linear B-cell epitope of the E2 protein. The motif (773)FDGTNP(778) is the minimal requirement for the reactivity as demonstrated by analysis of the reactivity of HQ06 with several truncated peptides derived from the motif. Alignment of amino acid sequences from a number of CSFV isolates indicated that the epitope is well conserved among different subgroups of CSFV. Substitutions of the individual residues within the epitope (773)FDGTNP(778) demonstrated that residues (773)F, (775)G, and (778)P constitute the core of the epitope. The identified epitope will be useful for development of diagnostic assays and epitope-based marker vaccines against CSFV.

[Differences in glycosylation of the E2 protein between virulent Shimen strain and a virulent C-strain of classical swine fever virus].

The E2 envelope glycoprotein of virulent Shimen strain and avirulent C-strain of Classical swine fever virus (CSFV) has 5 and 6 potential glycosylation sites, respectively, and the potential glycosylation site 986N is unique to C-strain. To study the differences in glycosylation between the virus pair, the E2 genes (removing signal sequence and transmembrane anchor regions) of the two strains fused with the melittin signal sequence were expressed in the Sf9 insect cells. The recombinant E2 proteins were secreted into the medium of Sf9 cells in dimer form with different molecular weight (MW). Deglycosylation of the recombinant E2 proteins by endo H and PNGase F showed that the deglycosalated Shimen-E2 and HCLV-E2 have the same MW, indicating that the different MW between Shimen-E2 and HCLV-E2 proteins came from different glycosylation. Site-directed mutagenesis in the potential glycosylation site at 986N demonstrated that the mutated Shimen-E2 protein had the same MW as the wild-type HCLV-E2 protein, while the mutated HCLV-E2 had the same MW as the wild-type Shimen-E2 protein. We suggest that the different MW between Shimen-E2 and HCLV-E2 is resulted from the different glycosylation on 986 N glycosylation site.