Plasmodium berghei XAT: Protective 155/160kDa antigens are located in parasitophorous vacuoles of schizont-stage parasite

The protective effect of CD40 ligand-CD40 signalling is limited during the early phase of Plasmodium infection

γδ T cells are essential for eliminating Plasmodium berghei XAT. Because administration of the agonistic anti-CD40 antibody can induce elimination of P. berghei XAT parasites in γδ T cell-deficient mice, we considered that γδ T cells might activate dendritic cells via CD40 signalling during infection. Here we report that administration of the anti-CD40 antibody to γδ T cell-deficient mice 3-10 days post-P. berghei XAT infection could eliminate the parasites. Our data suggest that dendritic cell activation via γδ T cells expressing CD40 ligand is critical during the early phase of infection.

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.