The protective immune response induced by B cell epitope of classical swine fever virus glycoprotein E2

Classical swine fever virus (CSFV) envelope glycoprotein E2 is a major protective immunogen responsible for eliciting neutralizing antibodies and conferring protective immunity against the virus. Based on the core sequence (TAVSPTTLR, 829-837 aa) of the B cell linear epitope of the CSFV E2 protein identified by Lin et al., two oligonucleotides MF and MR were synthesized and used to construct by PCR a gene cassette encoding a 15 amino acid polypeptide M (CTAVSPTTLRTEVVK), which spans 828-842 amino acids of E2. The gene cassette was fused in-frame to 3' terminal of glutathione S transferase gene (GST) of the prokaryotic expression vector pGEX-6p-1, resulting in the recombinant plasmid pGEX-M. After transformation into Escherichia coli BL21 a soluble fusion protein GST-M with expected size of 28 kDa was expressed after inducing with isopropyl-beta-d-thiogalactoside (IPTG). Enzyme-linked immunosorbent assay (ELISA) and Western blot analysis showed that the purified GST-M had good reactivity with swine anti-CSFV serum and rabbit anti-CSFV E2 serum. Further vaccination trials showed that the fusion protein GST-M could elicit effectively immune response protecting rabbits and pigs from virulent challenge. This study showed a possibility for developing epitope-based vaccines against CSFV.