A blood stage fraction of Plasmodium berghei induces protective and long lasting immune response in BALB/c mice.

Incorporation of the parasite's subcellular fractions in subunit vaccines can be a possible approach for formulation of vaccine against malaria. In this study, the immunogenicity and protective efficacy of 10,000g fraction of blood stage Plasmodium berghei was evaluated in mouse model. This fraction induced higher levels of anti-parasite antibodies and provided complete and long lasting protection as compared to whole parasite antigens. Antiserum raised against it was immunoadsorbed on CNBr activated sepharose-4B to elute antigens from this fraction. Eluted antigens were characterized electrophoretically, and after lyophilization these were designated as ML-I (having 55, 64, 66, and 74kDa proteins), ML-II (having 51, 64, 66, and 72kDa proteins) and ML-III (having only 47kDa protein) sub-fractions. Mice were immunized with these sub-fractions and immune responses induced by various immunization regimens were evaluated and compared with that of 10,000g fraction. These sub-fractions imparted partial protection except ML-III, which was non-protective. 10,000g fraction as a whole provided complete protection and generated significantly higher level of IL-2 and IFN-γ in immune mice. ML-I produced significant amount of IL-1 and IL-4 as compared to ML-II. Enhanced level of malaria-specific IgG1 was produced by ML-II, but IgG2a was significantly higher in ML-I immunized mice. Conclusively, this study identifies 10,000g fraction as a promising blood stage vaccine candidate and suggests that a vaccine based upon multiple antigens may be more efficacious as compared to single antigen based formulations.