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Expression of disulphide-bridge-dependent conformational epitopes and immunogenicity of the carboxy-terminal 19 kDa domain of Plasmodium yoelii merozoite surface protein-1 in live attenuated Salmonella vaccine strains

Abstract:

The 19 kDa carboxy-terminal domain of Plasmodium yoelii merozoite surface protein-1 (MSP119) was expressed in Salmonella vaccine strains as a carboxy-terminal fusion to fragment C of tetanus toxin (TetC). This study demonstrates that antibodies that recognize disulphide-dependent conformational epitopes in native MSP1 react with the TetC-MSP119 fusion protein expressed in Salmonella. The proper folding of MSP119 polypeptide is dependent on both the Salmonella host strain and the protein to which the MSP119 polypeptide is fused. Serum from mice immunized with Salmonella typhimurium C5aroD expressing TetC-MSP119 recognized native MSP1 as shown by immunofluorescence with P. yoelii-infected erythrocytes. Antibody levels to MSP119 were highest in out-bred mice immunized with S. typhimurium C5aroD carrying pTECH2-MSP119 and antibody was mostly directed against reduction-sensitive conformational epitopes. However, antibody levels were lower than in BALB/c mice immunized with a glutathione S-transferase (GST)-MSP119 fusion protein in Freund's adjuvant, and which were protected against P. yoelii challenge infection. In challenge experiments with P. yoelii the Salmonella-immunized mice were not protected, probably reflecting the magnitude of the antibody response. The results of this study have important implications in the design of live multivalent bacterial vaccines against eukaryotic pathogens.