TEMPORAL VARIATION OF THE MEROZOITE SURFACE PROTEIN-2 GENE OF PLASMODIUM-FALCIPARUM

Extensive polymorphism of key parasite antigens is likely to hamper th e effectiveness of subunit vaccines against Plasmodium falciparum infe ction. However, little is known about the extent of the antigenic repe rtoire of naturally circulating strains in different areas where malar ia is endemic. To address this question,,ve conducted a study in which blood samples were collected from parasitemic individuals living with in a small hamlet in Western Irian Jaya and Subjected to PCR amplifica tion using primers that would allow amplification of the gene encoding merozoite surface protein-2 (MSP2). We determined the nucleotide sequ ence of the amplified product and compared the deduced amino acid sequ ences to sequences obtained from samples collected in the same hamlet 29 months previously. MSP2 genes belonging to both major allelic famil ies were observed at both time points. In the Case of the FC27 MSP2 fa mily, we observed that the majority of individuals were infected by pa rasites expressing the same form of MSP2. Infections with parasites ex pressing 3D7 MSP2 family alleles were more heterogeneous. No MSP2 alle les observed at the earlier time point were detectable at the later ti me point, either for the population as a whole or for individuals who were assayed at both time points. We examined a subset of the infected patients by using blood samples taken between the two major surveys. In no patients could we detect reinfection by a parasite expressing a previously encountered form of MSP2. Our results are consistent with t he possibility that infection induces a form of strain-specific immune response against the MSP2 antigen that biases against reinfection by parasites bearing identical forms of MSP2.