Immunogenicity and immunizing protection effect of GAMA gene DNA vaccine on Plasmodium berghei

To explore the effect of immunogenicity and immunizing protection of GAMA gene DNA vaccine, which was related with merozoite, ookinete and sporozoite invasion.

Gene fragments were obtained using PCR technique and eukaryotic expression vector (containing immunostimulatory sequence) was built. BALB/c mice were divided into PBS control group, empty vector control group and study group and were immunized at week 0, 3 and 6 respectively. Blood was collected 2 weeks after each immunization and serum was separated to detect the IgG, IgG1 and IgG2a levels. Spleen of mice was obtained for preparation of splenic mononuclear cell and the cytokine IL-4 and IFN-γ levels were detected. Indirect immunofluorescence and western blot were employed to verify the specificity of antiserum. Sporozoite and merozoite invasion were used respectively to detect the immune protective effect 2 weeks after the third immunization. Ookinete conversion rate in vitro and oocyst numbers of mosquito stomach were observed to evaluate the transmission-blocking levels.

In GAMA DNA vaccine group: antiserum could be combined with recombinant protein specifically and green fluorescence signals of merozoite, ookinete and sporozoite were observable, while specific fragments and fluorescence signals were not observable in empty vector group. Compared with control group, specific IgG in DNA vaccine immunity group significantly increased (P < 0.01), and IgG1 and IgG2a all increased (P < 0.01). IL-4, IFN-γ content in study group significantly increased, compared with control group (P < 0.01). GAMA DNA vaccine immunity could not obviously block the erythrocyte-stage infection (caused by sporozoite invasion); compared with control group, liver worm load was slightly reduced (P < 0.05), and antiserum ookinete numbers (cultured in vitro) had no significant difference with oocyst numbers of mosquito stomach in DNA vaccine group.

GAMA has good antigenicity, which could stimulate the body to produce specific immune responses; while DNA vaccine immunity could not play a good protective effect, the effect of which is only limited to the slight reduction of liver worm load, and has no obvious erythrocyte-stage protective effect and transmission-blocking effect. Therefore, trying other immunization strategies for further research on the value of GAMA (as multi-stage antigen vaccine and multi-stage combined vaccine components of the life-cycle of plasmodium) is necessary.