Immunogenicity of a 40kDa fragment of the 47kDa recombinant protein and DNA vaccine from Karp strain of Orientia tsutsugamushi.

In this study, the fragment of 47 kDa gene (301 bp-1428 bp) was cloned into a prokaryotic expression vector pBV220 to construct a recombinant plasmid pBV-47. The E. coli cells were transformed with pBV-47 and the transformants were induced to express the recombinant protein at 42 degrees C. The expression product (40 kDa) was detected by SDS-PAGE analysis and the 40kDa protein was recognized by mouse polyclonal antibodies against O. tsutsugamushi Karp strain in western blot analysis. The entire 47 kDa protein gene was inserted into an eukaryotic expression vector pcDNA3.1(+) to construct a recombinant plasmid pcDNA3.1/47 and Balb/c mice were immunized with recombinant pcDNA3.1/47, control vector pcDNA3.1, PBS buffer, 40 kDa protein, and recombinant pcDNA3.1/47 plus 40 kDa protein (pcDNA3.1/47/40), respectively. The results showed that spleen cells from pcDNA3.1/47/40-immunized mice gave higher proliferation than other groups. A significant IgG rise was detected in mice immunized with 40 kDa protein, but it was less strong than that in mice immunized with pcDNA3.1/47/40. The results suggested that immunization with pcDNA3.1/47 and 40 kDa protein simultaneously could induce a strong immune response.