DNA immunization with Plasmodium falciparum serine repeat antigen: regulation of humoral immune response by coinoculation of cytokine expression plasmid.

We immunized mice with plasmid expressing the 47-kDa amino-terminal domain of the Plasmodium falciparum serine repeat antigen (SERA) using gene gun and investigated humoral immune response to SERA antigen. Significant SERA-specific IgG was observed in BALB/c mice after immunization three times with SERA expression plasmid. Furthermore, these levels were increased by the coinoculation of cytokine (IFN-gamma, IL-4, GM-CSF, or IL-12) expression plasmid. In respect to the SERA-specific Ig subclasses, coinoculation of IFN-gamma, GM-CSF, or IL-12 expression plasmid increased the levels of SERA-specific IgG2a, and these were much higher than that in mice immunized with SERA expression plasmid alone. In contrast to the SERA-specific IgG2a, coinoculation of any cytokine expression plasmid did not change the levels of SERA-specific IgG1. These results indicate that cytokine expression plasmid enhances and regulates humoral immune response elicited by SERA DNA immunization.