Polymorphism at the apical membrane antigen 1 locus reflects the world population history of Plasmodium vivax

<p>Abstract</p> <p>Background</p> <p>In malaria parasites (genus <it>Plasmodium</it>), <it>ama-1 </it>is a highly polymorphic locus encoding the Apical Membrane Protein-1, and there is evidence that the polymorphism at this locus is selectively maintained. We tested the hypothesis that polymorphism at the <it>ama-1 </it>locus reflects population history in <it>Plasmodium vivax</it>, which is believed to have originated in Southeast Asia and is widely geographically distributed. In particular, we tested for a signature of the introduction of <it>P. vivax </it>into the New World at the time of the European conquest and African slave trade and subsequent population expansion.</p> <p>Results</p> <p>One hundred and five ama<it>-1 </it>sequences were generated and analyzed from samples from six different Brazilian states and compared with database sequences from the Old World. Old World populations of <it>P. vivax </it>showed substantial evidence of population substructure, with high sequence divergence among localities at both synonymous and nonsynonymous sites, while Brazilian isolates showed reduced diversity and little population substructure.</p> <p>Conclusion</p> <p>These results show that genetic diversity in <it>P. vivax </it>AMA-1 reflects population history, with population substructure characterizing long-established Old World populations, whereas Brazilian populations show evidence of loss of diversity and recent population expansion.</p> <p>Note</p> <p>Nucleotide sequence data reported is this paper are available in the GenBank™ database under the accession numbers <ext-link ext-link-type="gen" ext-link-id="EF031154">EF031154</ext-link> – <ext-link ext-link-type="gen" ext-link-id="EF031216">EF031216</ext-link> and <ext-link ext-link-type="gen" ext-link-id="EF057446">EF057446</ext-link> – <ext-link ext-link-type="gen" ext-link-id="EF05487">EF057487</ext-link></p

Increased polyclonal immunoglobulin reactivity toward human and bacterial proteins is associated with clinical protection in human Plasmodium infection

BACKGROUND: Polyclonal B-cell activation is well known to occur in Plasmodium infections, but its role in pathogenesis or protection remains unclear. However, protective properties of natural antibodies have previously been demonstrated in other contexts. METHODS: Sera from asymptomatic and symptomatic Plasmodium-infected subjects locally detected in a survey study in the Brazilian Amazon, and from unexposed and exposed but presently uninfected control subjects, were assayed by a standardized quantitative immunoblot method allowing simultaneous detection of IgG or IgM reactivity to a large number of parasite-unrelated proteins. RESULTS: In subjects free of coinfection with hepatitis B virus, IgG reactivity to human brain antigens and Escherichia coli proteins was strikingly enhanced in asymptomatic Plasmodium-infected individuals when compared to such with clinical malaria symptoms, or to uninfected control subjects. This difference was most characteristic for limited exposure times (less than ten years locally, or 20 years in endemic areas). It was more significant than a similar trend found for IgG to Plasmodium falciparum antigens, and unrelated to parasitaemia levels. Asymptomatic subjects with comparatively short exposure characteristically showed relatively elevated IgG versus IgM reactivity. Polyclonal IgG reactivity appears triggered by previous P. falciparum but not Plasmodium vivax malaria. CONCLUSION: The observed difference in polyclonal antibody production seems related to intrinsic activation states of infected individuals, rather than to parasite-antigen specific immune responses. However, it appears influenced by preceding stimuli. This supports the idea that acquired clinical immunity may not exclusively depend on antigen-specific responses, but also on the individual polyclonal reaction

Allele-specific antibodies to Plasmodium vivax merozoite surface protein-1: prevalence and inverse relationship to haemoglobin levels during infection.

BACKGROUND: Antigenic polymorphisms are considered as one of the main strategies employed by malaria parasites to escape from the host immune responses after infections. Merozoite surface protein-1 (MSP-1) of Plasmodium vivax, a promising vaccine candidate, is a highly polymorphic protein whose immune recognition is not well understood. METHODS AND RESULTS: The IgG responses to conserved (MSP-119) and polymorphic (block 2 and block 10) epitopes of PvMSP-1 were evaluated in 141 P. vivax infected patients. Ten recombinant proteins corresponding to block 2 (variants BR07, BP29, BP39, BP30, BEL) and block 10 (BR07, BP29, BP39, BP01, BP13) often observed in Brazilian P. vivax isolates were assessed by ELISA in order to determine levels of specific antibodies and their respective seroprevalence. The magnitude and the frequency of variant-specific responses were very low, except for BR07 variant (>40%), which was the predominant haplotype as revealed by block 10 PvMSP-1 gene sequencing. By contrast, 89% of patients had IgG against the C-terminal conserved domain (PvMSP-119), confirming the high antigenicity of this protein. Using multiple linear and logistic regression models, there was evidence for a negative association between levels of haemoglobin and several IgG antibodies against block 2 variant antigens, with the strongest association being observed for BP39 allelic version. This variant was also found to increase the odds of anaemia in these patients. CONCLUSIONS: These findings may have implications for vaccine development and represent an important step towards a better understanding of the polymorphic PvMSP-1 domain as potential targets of vaccine development. These data highlight the importance of extending the study of these polymorphic epitopes of PvMSP-1 to different epidemiological settings

Multiple-Clone Activation of Hypnozoites Is the Leading Cause of Relapse in <em>Plasmodium vivax</em> Infection

<div><h3>Background</h3><p><em>Plasmodium vivax</em> infection is characterized by a dormant hepatic stage, the hypnozoite that is activated at varying periods of time after clearance of the primary acute blood-stage, resulting in relapse. Differentiation between treatment failure and new infections requires characterization of initial infections, relapses, and clone multiplicity in vivax malaria infections.</p> <h3>Methodology/Principal Findings</h3><p>Parasite DNA obtained from primary/relapse paired blood samples of 30 patients with <em>P. vivax</em> infection in Brazil was analyzed using 10 molecular markers (8 microsatellites and MSP-1 blocks 2 and 10). Cloning of PCR products and genotyping was used to identify low-frequency clones of parasites. We demonstrated a high frequency of multiple-clone infections in both primary and relapse infections. Few alleles were identified per locus, but the combination of these alleles produced many haplotypes. Consequently, the majority of parasites involved in relapse showed haplotypes that were distinct from those of primary infections. <em>Plasmodium vivax</em> relapse was characterized by temporal variations in the predominant parasite clones.</p> <h3>Conclusions/Significance</h3><p>The high rate of low frequency alleles observed in both primary and relapse infections, along with temporal variation in the predominant alleles, might be the source of reported heterologous hypnozoite activation. Our findings complicate the concept of heterologous activation, suggesting the involvement of undetermined mechanisms based on host or environmental factors in the simultaneous activation of multiple clones of hypnozoites.</p> </div

Detection of multiple-clone <i>P. vivax</i> infections using a panel of 10 markers.

<p>(A) Number and percent of malaria episodes showing multiple-clone infections detected by different numbers of markers. (B) Minimum number of markers able to detect all multiple clone infections was five: MS01 (77%), MS01+ MS07 (92%), MS01+ MS07+ MSPBl2 (97%), MS01+ MS07+ MSPBl2+ MS11 (98%), MS01+ MS07+ MSPBl2+ MS11+ MS08 (100%).</p

Genotyping of <i>P. vivax</i> primary/relapse paired parasites from 30 patients using 10 molecular markers.

<p>(A) Haplotype derived from predominant allele of each marker. Totally homologous – parasites showing all markers with the same allele; Homologous or Related – parasites with 8 to 9 markers with the same allele; Heterologous – parasites showing less than 8 markers with the same allele (according to Orjuela-Sánchez et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0049871#pone.0049871-OrjuelaSnchez1" target="_blank">[21]</a>). In patients with more than one relapse episodes, relapse parasites were compared with the previous acute malaria episode. (B) Percent of acute malaria episodes showing different amounts of markers with the same alleles, taking into account only the predominant allele from each marker (left) or all alleles, predominant and rare from each marker (right).</p