Abstract
BackgroundMalaria caused by Plasmodium vivax is a major public health problem worldwide that affects 70-80 million people in the Middle East, Asia, Western Pacific, South America and the Caribbean. Despite its epidemiological importance, few antigens from this parasite species have been characterized to date compared to Plasmodium falciparum, due in part to the difficulties of maintaining an in vitro culture of P. vivax. This study describes the identification of the P. falciparum thrombospondin-related apical merozoite protein homologue in P. vivax (PvTRAMP) and examines its potential to be further evaluated as vaccine candidate.MethodsThe gene encoding PvTRAMP was identified through an extensive search of the databases hosting the genome sequence of P. vivax. Genes adjacent to pvtramp were identified in silico to determine the degree of similarity between the protein sequences encoded by equivalent chromosomic fragments in P. falciparum and Plasmodium knowlesi. The pvtramp gene was amplified from cDNA of P. vivax schizont stages, cloned and expressed in Escherichia coli. Anti-PvTRAMP antisera was obtained by inoculating rabbits with PvTRAMP B cell epitopes produced as synthetic peptides in order to assess its recognition in parasite lysates by Western blot and in intact parasites by indirect immunofluorescence. The recognition of recombinant PvTRAMP by sera from P. vivax-infected individuals living in endemic areas was also assessed by ELISA.ResultsThe PfTRAMP homologue in P. vivax, here denoted as PvTRAMP, is a 340-amino-acid long antigen encoded by a single exon that could have a potential role in cytoadherence, as indicated by the presence of a thrombospondin structural homology repeat (TSR) domain. According to its transcription and expression profile, PvTRAMP is initially located at the parasite's apical end and later on the parasite surface. Recombinant PvTRAMP is recognized by sera from infected patients, therefore, indicating that it is targeted by the immune system during a natural infection with P. vivax.ConclusionsThe results of this work support conducting further studies with PvTRAMP to evaluate its immunogenicity and protection-inducing ability in the Aotus animal model.
Highlights
Malaria caused by Plasmodium vivax is a major public health problem worldwide that affects 70-80 million people in the Middle East, Asia, Western Pacific, South America and the Caribbean
P. falciparum malaria accounting for over 1 million deaths and around 300 million new cases annually [1], while P. vivax malaria has long been neglected and mistakenly considered a “benign” disease, but it is gaining importance as it causes a considerable number of cases (~70-80 million cases per year), especially in the Middle East, Asia, the Western Pacific, South America and the Caribbean
The alignment showed homology between the open reading frames (ORFs) encoding PvTRAMP and PfTRAMP, as well as high overall identity (Id) and similarity (S) values between the protein sequences derived from pvtramp, pftramp and pktramp (Id = 54.55% and S = 83.25%)
Summary
Malaria caused by Plasmodium vivax is a major public health problem worldwide that affects 70-80 million people in the Middle East, Asia, Western Pacific, South America and the Caribbean. The release of the complete genome sequences of P. falciparum and P. vivax [5,6], their corresponding transcriptome profiles [7,8], and the analysis of the P. falciparum proteome [9,10] have promoted studies aimed at identifying proteins involved in parasite invasion to host cells, such as proteins of the secretory apical organelles and surface proteins of bloodstage parasites Based on this large body of available data, recent research in P. vivax malaria has made use of bioinformatics tools to identify and characterize new potential anti-malarial vaccine candidates by homology comparison (e.g. P_vivax vs P. falciparum) [11,12,13,14]
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