Plasmodium vivax: dimorphic DNA sequences from the MSP-1 gene code for regions that are immunogenic in natural infections.

The merozoite surface protein 1 gene of Plasmodium vivax (PvMSP-1) is becoming a solid genetic marker for studying the polymorphism of natural parasite populations from this prevalent human malaria. Indeed, a conserved and a variant PvMSP-1 gene segments have been amplified from total genomic parasite DNA obtained from isolates representing seven countries and three continents. Interestingly, the variant PvMSP-1 gene segment contains two highly conserved parental allele forms capable of limited genetic exchange at the sexual stage in the mosquito vector. This variant PvMSP-1 gene segment was amplified from 18 Colombian isolates to try to determine whether the same two parental allele forms were also present in this geographical area. Southern blot and DNA sequencing analyses confirmed their existence among the Colombian isolates. Moreover, expression of these two allele forms as recombinant proteins allowed us to demonstrate for the first time that this PvMSP-1 gene segment codes for amino acid sequences that are exposed on the surface of P. vivax schizonts and that are immunogenic in natural infections.