Abstract
BackgroundPlasmodium knowlesi is the fifth species identified to cause malaria in humans and is often misdiagnosed as Plasmodium malariae due to morphological similarities. The development of an inexpensive, serological detection method utilizing antibodies specific to P. knowlesi would be a valuable tool for diagnosis. However, the identification of specific antigens for these parasites remains a major challenge for generating such assays. In this study, surface protein containing an altered thrombospondin repeat domain (SPATR) was selected as a potentially specific antigen from P. knowlesi. Its multistage expression by sporozoites, asexual erythrocytic forms and gametocytes, along with its possible role in liver cell invasion, suggests that SPATR could be used as a biomarker for diagnosis of P. knowlesi.MethodsThe spatr gene from P. knowlesi was codon optimized and cloned (pkhspatr). Recombinant pkHSPATR protein was expressed, purified, and evaluated for its sensitivity and specificity in immunoblot and ELISA-based assays for detecting P. knowlesi infection.ResultsThe recombinant pkHSPATR protein allows sensitive detection of human P. knowlesi infection in serum samples by immunoblot and ELISA.ConclusionsWith further research, recombinant pkHSPATR protein could be exploited as a marker for detection of P. knowlesi infection in humans. Therefore, this finding should contribute to the development of immunodiagnostic assays for the species-specific detection of malaria.
Highlights
Plasmodium knowlesi is the fifth species identified to cause malaria in humans and is often misdiagnosed as Plasmodium malariae due to morphological similarities
The development of an inexpensive, serological detection method utilizing antibodies specific to P. knowlesi would be a valuable tool for diagnosis of knowlesi malaria
Polymerase chain reaction (PCR) and cloning The P. knowlesi spatr gene sequence was identified in a BLAST search of the P. knowlesi database using the published sequence of P. falciparum spatr [GenBank: AY952327] as a query sequence
Summary
Plasmodium knowlesi is the fifth species identified to cause malaria in humans and is often misdiagnosed as Plasmodium malariae due to morphological similarities. Surface protein containing an altered thrombospondin repeat domain (SPATR) was selected as a potentially specific antigen from P. knowlesi. The phylum Apicomplexa comprises a large group of protists, including Babesia, Plasmodium, Cryptosporidium and Toxoplasma, which are characterized by specialized secretory organelles found at their apical prominence These apical structures, consisting of micronemes, rhoptries, and dense granules [4], contain many proteins that are involved in parasite motility and host cell invasion. An altered version of the thrombospondin repeat domain was first found in Plasmodium yoelii [6,7] and named the surface protein of altered thrombospondin repeat (SPATR) Orthologue of this protein has been identified in P. knowlesi and named the pkSPATR
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