Abstract
BackgroundPlasmodium falciparum antigenic diversity and polymorphism confuses the issue of antimalarial vaccine development. Merozoite surface protein (MSP)-1 and -2 are two highly polymorphic vaccine candidates. Characterisation of their precise polymorphism in endemic regions may facilitate the design of an effective vaccine.MethodsIsolates obtained in 52 Gabonese children presenting with uncomplicated malaria were genotyped by nested-PCR of msp-1 block 2, and msp-2 block 3, to analyze both parasite population polymorphism and clone fluctuations.ResultsTwenty-five and 19 different alleles were respectively obtained for msp-1 and msp-2 loci, the RO33 family of msp-1 being poorly polymorphic. Four cases of non-random distribution of alleles were reported of the FC27, and/or 3D7 families of msp-2. All but two isolates were composed of more than one genotype, and the multiplicity of infection (MOI) was 4.0. Neither parasite density nor age was related to MOI. Clone fluctuations were studied for ten subjects who were sampled again at reappearance of parasites in blood. Disappearance and reappearance of alleles were observed following treatment, suggesting difficulties in assessing polymorphism and in distinguishing reinfection from recrudescence.ConclusionP. falciparum polymorphism is extensive in Southeast Gabon, and most of infections are composed of multiple clones. The fluctuation of clones contributes to parasite diversity.
Highlights
Plasmodium falciparum antigenic diversity and polymorphism confuses the issue of antimalarial vaccine development
One main limitation to the development of a vaccine against Plasmodium falciparum is the antigenic diversity related to P. falciparum polymorphism
Perhaps as part of an immune evasion mechanism, msp-119 and msp-2 DNA sequences include variable blocks generating antigenically diverse forms [4,5]. The polymorphism at these two loci is mainly assessed by the number of repeats [6,7,8], which can be used to distinguish by size the different alleles after PCR amplification
Summary
Plasmodium falciparum antigenic diversity and polymorphism confuses the issue of antimalarial vaccine development. Merozoite surface protein (MSP)-1 and -2 are two highly polymorphic vaccine candidates. Merozoite surface protein (MSP)-1 and MSP-2 are two proteins causing immune response in humans [1,2,3,4] and are prime vaccine candidates. Perhaps as part of an immune evasion mechanism, msp-119 and msp-2 DNA sequences include variable blocks generating antigenically diverse forms [4,5]. The polymorphism at these two loci is mainly assessed by the number of repeats [6,7,8], which can be used to distinguish by size the different alleles after PCR amplification. Strain-specific immunity is largely responsible for protective immunity (page number not for citation purposes)
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