Immunization against malaria with a recombinant protein.

We have expressed in bacteria the C-terminal part of Plasmodium yoelii merozoite surface protein-1 (MSP1) containing the two epidermal growth factor-like domains. The protein, either alone or fused to glutathione S-transferase, was highly effective as a vaccine and protected mice against challenge infection. Reduction and alkylation abolished the protection obtained with the protein. This shows for the first time the absolute requirement of the disulphide-bonded conformation for immunogenicity. In a short term experiment, mice were protected against a massive challenge. The immunity was effective at the time of merozoite release/reinvasion. Recombinant protein based on this part of MSP1 may be suitable as a vaccine against malaria.