UC San Diego

This work explored sexual development of the lethal human malaria parasite, Plasmodium falciparum. A method to cultivate Plasmodium falciparum sexual stage parasites in vitro was optimized and increased ookinete yield > 20-fold over previous reports. This method was adapted for Plasmodium vivax, a neglected human malaria parasite, and found to generate Plasmodium vivax ookinetes. The method was essential for investigation of the role of a novel aspartic protease, Plasmepsin X, in sexual stage parasite development. Antibodies to Plasmepsin X were found to significantly decrease Plasmodium transmission to mosquitoes by 20-40% in vivo but did not affect ookinete development in vitro. This was the first demonstration that a non-food vacuole plasmepsin facilitated Plasmodium falciparum midgut infection of mosquitoes. Finally, the numbers of parasites generated with this method were sufficient for proteomic analysis of sexual stage parasites. The Plasmodium falciparum zygote and ookinete proteome has never before been available, and this was the first time that any stage of Plasmodium vivax has been analyzed using a proteomic approach. The ability to generate Plasmodium falciparum sexual stage parasites, especially zygotes and ookinetes, has permitted detailed molecular analyses essential for transmission-blocking vaccine studies as well as global analyses that generated insights into Plasmodium sexual stage biology