BIOLOGY OF MALARIA SPOROZOITES IN THE MOSQUITO VECTOR

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The long-term goal of the proposed research is to understand malaria sporozoite passage through the mosquito hemocoel and invasion of the salivary glands, which are required for parasite transmission to a new host. This period remains a little-studied but critical interval of the malaria life cycle. Disrupting the essential receptor-ligand binding necessary for gland invasion may be a new approach for vector-based control of malaria transmission. The specific aims are to: 1) Molecularly characterize candidate salivary gland receptors for sporozoite invasion. We have 25 hybridoma lines that produce monoclonal antibodies (mAbs) specific for molecules on the surface of Aedes aegypti salivary glands. Several mAbs inhibit Plasmodium gallinaceum sporozoite invasion into glands, and thus are candidate receptors. We will identify the molecules identified by the gland-specific mAbs, clone their cognate cDNAs, and raise polyclonal antibodies against recombinant protein. 2) Test the biological function of candidate sporozoite receptors by an in vivo assay for invasion blocking. Purified sporozoites will be inoculated into the hemocoel of uninfected mosquitoes, along with polyclonal antibodies directed against candidate receptors. The inhibition of sporozoite invasion by specific antibodies relative to controls will identify presumptive receptor molecules that are necessary for sporozoite invasion to occur. 3) Determine the fate of non-invaded sporozoites in the mosquito hemocoel. Our preliminary results indicate that sporozoites that do not invade the salivary glands, are probably destroyed in the hemocoel. Identifying the site of sporozoite destruction is a first step to understanding the cellular and molecular basis of a potential specific immune response and exploiting it in malaria transmission control. We have made a line of Plasmodium berghei genetically transformed to produce fluorescent sporozoites. We will infect Anopheles gambiae with these parasites and will then track and quantify the fluorescent sporozoites in the mosquitoes by confocal microscopy to identify the sites and cellular mechanism of sporozoite destruction. Overall, we propose that there is a competition in the hemocoel between the processes of sporozoite destruction and gland invasion. By blocking gland invasion and/or enhancing destruction, it may ultimately be possible to manipulate this dynamic state to decrease natural malaria transmission.