Abstract
The Plasmodium falciparum apical asparagine (Asn)-rich protein (AARP) is one of malarial proteins, and it has been studied as a candidate of malaria subunit vaccine. Basic characterization of PvAARP has been performed with a focus on its immunogenicity and localization. In this study, we further analyzed the immunogenicity of PvAARP, focusing on the longevity of the antibody response, cross-species immunity and invasion inhibitory activity by using the primate malaria parasite Plasmodium knowlesi. We found that vivax malaria patient sera retained anti-PvAARP antibodies for at least one year without re-infection. Recombinant PvAARP protein was strongly recognized by knowlesi malaria patients. Antibody raised against the P. vivax and P. knowlesi AARP N-termini reacted with the apical side of the P. knowlesi merozoites and inhibited erythrocyte invasion by P. knowlesi in a concentration-dependent manner, thereby suggesting a cross-species nature of anti-PvAARP antibody against PkAARP. These results can be explained by B cell epitopes predicted in conserved surface-exposed regions of the AARP N-terminus in both species. The long-lived anti-PvAARP antibody response, cross-reactivity, and invasion inhibitory activity of anti-PvAARP support a critical role of AARP during the erythrocyte invasion and suggest that PvAARP induces long-lived cross-species protective immunity against P. vivax and P. knowlesi.
Highlights
Plasmodium vivax, the most widely distributed malaria parasite, globally contributes to 16 million cases outside of Africa, and affects the economy of most developing countries[1]
PfAARP has orthologs in all reported Plasmodium species, including the P. vivax apical Asn-rich protein which has been reported as PvARP from previous study, here we refer as PvAARP (PVX_090210, Sal-1 strain)[23] and P. knowlesi apical Asn-rich protein (PkAARP, PKNH_0515300, H strain)
No transmembrane region and GPI-anchor motif were predicted for PvAARP and PkAARP or PfAARP, according to several robust transmembrane prediction algorithms such as TMHMM ver 2.0, Phobius, and OCTOPUS26–28, despite a previous report of a predicted transmembrane domain in PfAARP
Summary
Plasmodium vivax, the most widely distributed malaria parasite, globally contributes to 16 million cases outside of Africa, and affects the economy of most developing countries[1]. Recent studies have shown that PvAARP localizes on the surfaces of merozoites with accumulation on the apical side[21,24], in contrast to the rhoptry neck localization of PfAARP Both PvAARP and PkAARP contain a signal peptide sequence at their N-terminus and Asn- and proline (Pro)-rich regions toward the C-terminus. The antibody response against PvAARP was observed for up to one year in vivax malaria patients without re-infection These findings support a critical role of AARP during the erythrocyte invasion process by these parasites and suggest that PvAARP induces long-lived cross-species protective immunity against P. vivax and P. knowlesi
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