| Foot-and-mouth disease (FMD) is a kind of airborne and violent infectious disease with wide animal hosts. It is also infectious to human beings and follows with extensive interest as a zoonosis. Once FMD occurs, all the infected and exposed animals would be subjected to slaughter ("OIE Manual", 1996). An economic devastation might result from the massive animal death and the economic sanction from other countries on account of the FMD. Therefore, prevention of FMD is the only way to solve the problem. Although the conventional vaccines made by chemically inactivated whole viral particle have been efficiently controlled FMD in many countries, it was found to cause outbreaks of FMD by release of incompletely inactivated virus from the vaccine. Attempts to produce safer vaccines for FMD have been made on the synthesized peptides or bacterially expressed proteins contain viral epitopes. Although antibodies induced by these peptides or protein are able to efficiently neutralize the FMD virus in experimental animals, protection of livestock from virus challenge are not successful. However, DNA vaccines provide arr alternative because of its immunogenecity and significant advantages over conventional inactivated virus vaccine, in particular having none of the risks associated with the high security requirements for working with live virus.The FMD was caused by foot-and-mouth disease virus (FMDV), which is a member of the picornavirus family. The virus particle contains 60 copies of each of four structural proteins that designated VP1, 2, 3 and 4, respectively. They comprise the viral capsid named P1. The non-replicating DNA vaccine, encoding P1 and the processing (3C) proteinase, was reported to produce detectable antiviral immune response. On the contrast, the replicating DNA vaccine with the entire FMDV genome, undergoing amplification in susceptible cells, gave rise to a stronger immune response. Unfortunately, both DNA vaccines only partially (20%) protect swine from a highly virulent FMD challenge, which may due to the rapid inhibition of host cell protein synthesis mediated by the viral processing (3C) protease or the leader (L) protease. These two viral proteases were reported to induce cleavage of translation initiation factors eIF4A or eIF4G within host cells and the cleavage may result in host cells apoptosis.Therefore, many scientists focus their researching interests on DNA vaccine encoding epitopes. A recent study showed that swines inoculated with DNA vaccine containing FMDV Site 1 were 100 per cent protected against the viral infection. Site 1, the predominant site, encodes two VP1 epitopes, which was able to protect animals from viral attack The two epitopes are located at the positions from residues 141 to 160 and from 200 to 213 of VP1, respectively. However, the plasmid DNA encoding epitopes from Site 1 combination with other four sites on PI was far from clear. Those four sites, like site 1, containing B-cell epitopes, were also defined on the type O virion through monoclonal antibody escape mutantstudies. Site 3, encoding residues 40 to 60 of VP1, has been shown to modulate the function of epitopes encoded by site l(Parry et al.,1990). Moreover, Site 2(encoding residues 70 to 78 and 131 to 134 of VP2), Site 4 (encoding residues 56 to 58 on VP3) and site 5 (encoding residue 149) also made function differently.Here, we synthesized a multiple-epitopes gene (SG) according to the sequence of the five sites and the sequence encoding T-cell epitope (T site) of VP1 according to the sequence of type O FMDV in GENEBANK (accession no. X00871). Linkers, comprised of glycine and serine, were used to avoid the interference resulted from the direct ligation between each epitope or production of new epitopes. A plasmid DNA, designated pVAX-SG, was generated by cloning SG gene into EcoR I and Xba I sites of pVAX1 vector under control of the cytomegalovirus promoter. To determine the correct expression of B-cell epitopes encoded by pVAX-SG, the plasmid was transfected into PK1 cells and BHL-21 c...
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