Antibody responses to infections with strains of Plasmodium falciparum expressing diverse forms of merozoite surface protein 2

Individuals living in areas where Plasmodium falciparum is endemic experien ce numerous episodes of infection. These episodes map or may not be symptom atic, with the outcome depending on a combination of parasite and host fact ors, several of which are poorly understood. One factor is believed to be t he particular alleles of several parasite proteins to which the host is cap able of mounting protective immune responses. We report a study examining a ntibody responses to MSP2 in 15 semi-immune teenagers and adults living in the Khanh-Hoa area of southern-central Vietnam, where P. falciparum is high ly endemic; subjects were serially infected with multiple strains of P. fal ciparum. The MSP2 alleles infecting these subjects were determined by nucle otide sequencing. A total of 62 MSP2 genes belonging to both dimorphic fami lies were identified, of which 33 contained distinct alleles, with 61% of t he alleles being detected once. Clear changes in the repertoire occurred be tween infections. Most infections contained a mixture of parasites expressi ng MSP2 alleles from both dimorphic families. Two examples of reinfection w ith a strain expressing a previously encountered allele were detected. Sign ificant changes in antibody levels to various regions of MSP2 were detected over the course of the experiment. There was no clear relation between the infecting form of MSP2 and the ensuing antibody response. This study highl ights the complexity of host-parasite relationship for this important human pathogen.