Restricted genetic diversity of Plasmodium falciparum major merozoite surface protein 1 in isolates from Colombia

Longevity of Genotype-Specific Immune Responses to Plasmodium falciparum Merozoite Surface Protein 1 in Kenyan Children from Regions of Different Malaria Transmission Intensity

Naturally acquired immunity to Plasmodium falciparum presents a changing landscape as malaria control programs and vaccine initiatives are implemented. Determining which immunologic indicators remain surrogates of past infection, as opposed to mediators of protection, led us to compare stability of immune responses across regions with divergent malaria transmission intensities. A repeat cross-sectional study of Kenyan children from a malaria-holoendemic area and an epidemic-prone area was used to examine longitudinal antibody and interferon-gamma (IFN-γ) responses to the 3D7 and FVO variants of merozoite surface protein 1 (MSP1). Antibodies to MSP1 were common in both study populations and did not significantly wane over a 21-month time period. IFN-γ responses were less frequent and rapidly disappeared in children after a prolonged period of no malaria transmission. Antibody and IFN-γ responses rarely correlated with each other; however, MSP1-specific IFN-γ response correlated with lack of concurrent P. falciparum parasitemia of the same genotype, though only statistically significantly in the malaria-holoendemic region (odds ratio = 0.31, 95% confidence interval = 0.12-0.84). This study affirms that antimalarial antibodies are informative for evaluation of history of malaria exposure within individuals, whereas cell-mediated immunity, though short lived under natural exposure conditions, might provide an assessment of recent infection and protection from parasitemia.

Polymorphism of the merozoite surface protein-1 block 2 region in Plasmodium falciparum isolates from Mauritania

BACKGROUND

The genetic diversity of Plasmodium falciparum has been extensively studied in various parts of the world. However, limited data are available from Mauritania. The present study examined and compared the genetic diversity of P. falciparum isolates in Mauritania.

METHODS

Plasmodium falciparum isolates blood samples were collected from 113 patients attending health facilities in Nouakchott and Hodh El Gharbi regions. K1, Mad20 and RO33 allelic family of msp-1 gene were determined by nested PCR amplification.

RESULTS

K1 family was the predominant allelic type carried alone or in association with Ro33 and Mad20 types (90%; 102/113). Out of the 113 P. falciparum samples, 93(82.3%) harboured more than one parasite genotype. The overall multiplicity of infection was 3.2 genotypes per infection. There was no significant correlation between multiplicity of infection and age of patients. A significant increase of multiplicity of infection was correlated with parasite densities.

CONCLUSIONS

The polymorphism of P. falciparum populations from Mauritania was high. Infection with multiple P. falciparum clones was observed, as well as a high multiplicity of infection reflecting both the high endemicity level and malaria transmission in Mauritania.

Genetic diversity of Plasmodium falciparum merozoite surface protein-1 block 2 in sites of contrasting altitudes and malaria endemicities in the Mount Cameroon region

The present study analyzed the relationship between the genetic diversity of Plasmodium falciparum and parasitologic/entomologic indices in the Mount Cameroon region by using merozoite surface protein 1 as a genetic marker. Blood samples were collected from asymptomatic children from three altitude zones (high, intermediate, and low). Parasitologic and entomologic indices were determined by microscopy and landing catch mosquito collection/circumsporozoite protein-enzyme-linked immunosorbent assay, respectively. A total of 142 randomly selected P. falciparum-positive blood samples were genotyped by using a nested polymerase chain reaction-based technique. K-1 polymerase chain reaction products were also sequenced. As opposed to high altitude, the highest malaria prevalence (70.65%) and entomologic inoculation rate (2.43 infective/bites/night) were recorded at a low altitude site. Seven (18.91%), 22 (36.66%), and 19 (42.22%) samples from high, intermediate, and low altitudes, respectively, contained multiclonal infections. A new K-1 polymorphism was identified. This study shows a positive non-linear association between low/intermediate altitude (high malaria transmission) and an increase in P. falciparum merozoite surface protein 1 block 2 polymorphisms.

Diversity and prevalence of the C-terminal region of Plasmodium falciparum merozoite surface protein 1 in China

Malaria continues to be a significant health concern for regions of southeastern Asia. Scientists have focused much effort on the development and regional testing of a vaccine against the most virulent of the pathogens that cause the disease, Plasmodium falciparum. The 19kDa COOH-terminal region of the merozoite surface protein 1 (PfMSP1-19) is considered to be a potentially important component of a malaria vaccine and yet, to date, there is little data from China with regard to Pfmsp1-19 diversity. We have collected samples from 300 individuals diagnosed with P. falciparum infections from Yunnan and Hainan provinces--two potential vaccine trial sites in China. We determined the sequence of DNA encoding PfMSP1-19 for each. We identified seven polymorphic positions; varying arrangements of which accounted for 10 distinct Pfmsp1-19 haplotypes. Four haplotypes, however, represented more than 93% of the total. Differences in the prevalence of haplotypes between Yunnan and Hainan provinces were observed, even though the distribution of haplotypes in Yunnan province seemed to be very similar to those reported for Vietnam and Thailand. These results provide necessary information for the design of a major human vaccine trial as well as a basis for subsequent interpretations of the results. On broader scale, the data should complement the existing database on the prevalence and distribution of Pfmsp1-19 haplotypes and therefore have potential use in the design of PfMSP1-19-based polyvalent vaccines for use in Southeastern Asian countries.

Near-fixation of a Pfmsp1 block 2 allelic variant in genetically diverse Plasmodium falciparum populations across Western Colombia

Assessment of the genetic diversity of Plasmodium falciparum in 110 Colombian isolates revealed that nearly all the parasites in the 97 isolates collected in endemic regions west of the Andes shared the same Pfmsp1 block 2 MAD20-type allelic variant, despite showing high diversity for other genetical markers. Analysis of published data indicated that the prevalence of this allelic variant of a major vaccine candidate antigen was already dominant since 1998. This phenomenon, which had not been hitherto recorded for a malaria blood stage antigen, is of biological and immunological interest but remains unexplained.

Shift in epitope dominance of IgM and IgG responses to Plasmodium falciparum MSP1 block 4

Background

Plasmodium falciparum merozoite surface protein-1 (MSP1) has been extensively studied as a blood-stage malaria vaccine candidate, with most work focused on the conserved 19 kDa and semi-conserved 42 kDa C-terminal regions (blocks 16-17) and the hypervariable N-terminal repeat region (block 2). However, recent genotyping studies suggest that additional regions of MSP1 may be under selective pressure, including a locus of intragenic recombination designated as block 4 within the 3' region of the gene.

Methods

The current study examined the antibody response to the two parental and two recombinant forms of block 4 and to blocks 16-17 (3D7) in study populations from Colombia, Papua New Guinea and Cameroon that differ in malaria transmission intensity and ethnic composition.

Results

IgM and IgG antibodies were detected against parental and recombinant MSP1 block 4 peptides in all three populations. Overall, 32-44% of the individuals produced IgM to one or more of the peptides, with most individuals having IgM antibodies reactive with both parental and recombinant forms. In contrast, IgG seropositivity to block 4 varied among populations (range 15-65%), with the majority of antibodies showing specificity for one or a pair of block 4 peptides. The IgG response to block 4 was significantly lower than that to blocks 16-17, indicating block 4 is subdominant. Antibodies to block 4 and blocks 16-17 displayed distinct IgG subclass biases, with block 4 responses biased toward IgG3 and blocks 16-17 toward IgG1. These patterns of responsiveness were consistently observed in the three study populations.

Conclusions

Production of antibodies specific for each parental and recombinant MSP1 block 4 allele in different populations exposed to P. falciparum is consistent with balancing selection of the MSP1 block 4 region by the immune response of individuals in areas of both low and high malaria transmission. MSP1 block 4 determinants may be important in isolate-specific immunity to P. falciparum.