IMMUNIZATION WITH A RECOMBINANT C-TERMINAL FRAGMENT OF PLASMODIUM-YOELII MEROZOITE SURFACE PROTEIN-1 PROTECTS MICE AGAINST HOMOLOGOUS BUT NOT HETEROLOGOUS P-YOELII SPOROZOITE CHALLENGE

It has been reported previously that immunization with recombinant pro tein containing the two epidermal growth factor (EGF)-like modules fro m merozoite surface protein 1 (MSP-1) of Plasmodium yoelii (strain YM) protects mice against a lethal blood-stage challenge with the same pa rasite strain. Since MSP-1 is expressed in both liver-and blood-stage schizonts and on the surface of merozoites, we evaluated the effective ness of immunization with recombinant proteins containing either the i ndividual or the two combined EGF-like modules in producing a protecti ve response against a sporozoite challenge. The recombinant protein ex pressing the combined EGF-like modules of the YM strain protected mice against a homologous sporozoite challenge, and sterile protection, as defined by the absence of detectable blood-stage parasites, was obser ved in the majority of the mice. In contrast, mice immunized with reco mbinant P. yoelii YM MSP-1 were pot protected against a heterologous c hallenge with sporozoites from strain 265 BY of P. yoelii. The lack of protection may be explained by differences identified in the amino ac id sequences of MSP-1 for the two strains. A recombinant protein conta ining the two EGF-like modules of MSP-1 from P. yoelii 265 BY was prod uced and used to immunize mice. These mice were protected against a ho mologous challenge with sporozoites of P. yoelii 265 BY. The results s uggest that a recombinant MSP-1 has potential as a vaccine against mal aria, but its efficacy may be limited by sequence polymorphism and sel ection of variants.