Humoral immune response to Plasmodium falciparum merozoite surface protein 1 C-terminal region based hybrid nucleic acid vaccines in mice

Objective To analyze humoral immune response to nucleic acid vaccines (VR1012/TPA/ HG-MSP1-17 for intracellular expression or VR1012/HG-MSP1-17 for secretion) which contain Plasmodium falciparum Merozoite surface protein 1 (MSP1) 17 block gene and gene fragment of several T cell epitopes from MSA1, MSA2, RESA, IL-1 and TT and to monitor the effect of DNA-immune sera on parasite inhibition. Methods BALB/c or C57BL/6 mice received three intramuscular immunizations with 200μg/100μl or 100μg/100μl of VR1012/HG-MSP1-17 or VR1012/TPA/HG-MSP1-17 per mouse each time. HG or MSP1-17 antibodies were monitored by indirect ELISA. The effect of immune sera on parasite inhibition was monitored by in vitro inhibition assays. Results BALB/c and C57BL/6 mice immunized with 100μg/100μl of VR1012/HG-MSP1-17 per mouse gave significantly HG and MSP1-17 antibodies, but the levels of antibodies were not high. BALB/c mice immunized with 200μg/100μl of VR1012/HG-MSP1-17 per mouse gave higher HG antibodies but no change in MSP1-17 antibodies. BALB/c immunized with 200μg/100μl of VR1012/TPA/HG-MSP1-17 per mouse gave low level of HG antibodies and no MSP1-17 antibodies. Sera from the mice immunized with 200μg/100μl VR1012/HG-MSP1-17 could significantly inhibit Plasmodium falciparum growth. Conclusion VR1012/HG-MSP1-17 is more immunogenic than VR1012/TPA/HG-MSP1-17. The sera of VR1012/HG-MSP1-17 immunized mice could inhibit parasite growth prominently.