Abstract
BackgroundThe Plasmodium falciparum parasite is transmitted in its sexual gametocyte stage from man to mosquito and as asexual sporozoites from mosquito to man. Developing gametocytes sequester preferentially in the bone marrow, but mature stage gametocytes are released to the bloodstream. Sexual stage parasite surface proteins are of interest as candidate target antigens for transmission blocking vaccines.MethodsIn this study, the transcript profiles of rif and var genes, known to encode surface antigens in asexual blood stage parasites, were investigated at different stages of 3D7/NF54 gametocytogenesis and in sporozoites.ResultsGametocytes exhibited a rif transcript profile unlinked to the rif and var transcript profile of the asexual progenitors. At stage V, mature gametocytes produced high levels of a single rif gene, PF13_0006, which also dominated the rif transcript profile of sporozoites. All var genes appeared to be silenced in sporozoites.ConclusionsThe most prominent variant surface antigen transcribed in both gametocytes and sporozoites of 3D7/NF54 is a single variant of the RIFIN protein family. This discovery may lead to the identification of the parasites binding ligands responsible for the adhesion during sexual stages and potentially to novel vaccine candidates.
Highlights
The Plasmodium falciparum parasite is transmitted in its sexual gametocyte stage from man to mosquito and as asexual sporozoites from mosquito to man
Rif gene transcript profiles in mature gametocytes and sporozoites is dominated by PF13_0006 Plasmodium falciparum parasites were induced to develop into sexual gametocyte stages and the RNA was isolated for transcriptional analysis. 3D7 gametocytes were induced in three separate experiments to isolate stage II, III and V, whereas NF54 stage V gametocytes were available for one experiment
Rif transcript abundances increased as the parasites matured and transcripts of PF13_0006 and PFI0025c progressively dominated, with PF13_0006 being the most dominant at gametocyte stage V (Figure 1)
Summary
The Plasmodium falciparum parasite is transmitted in its sexual gametocyte stage from man to mosquito and as asexual sporozoites from mosquito to man. Developing gametocytes sequester preferentially in the bone marrow, but mature stage gametocytes are released to the bloodstream. Plasmodium falciparum is transmitted from infected humans to mosquitoes via sexual stages called gametocytes. Immature gametocytes arise from erythrocytic asexual stages and sequester preferentially in the bone marrow [1] for about 9-12 days before reaching maturity and emerging into peripheral blood [2]. Unlike other species of malaria parasites, five different stages of P. falciparum gametocyte development have been described in vitro by morphological criteria [2], known as stages I to V. At stage V are gametocytes released to the bloodstream and become infectious to mosquitoes of the Anopheles sp.
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