IMMUNE RESPONSES TO PLASMODIUM IN ANOPHELES GAMBIAE

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Malaria is the major vector-borne parasitic disease for much of the developing world and also threatens military personnel, tourists, business people and others who work in Africa, Asia and Latin America. Because of parasite and mosquito resistance to drugs and pesticides, new control strategies are needed. The long-term objective of the research is to understand the physiology, biochemistry, and genetics of mosquitoes that are resistant to malaria infections. This may suggest ways to replace natural populations with genetically transformed nonvector mosquitoes. A specific type of resistance is found in a genetically- selected strain of Anopheles gambiae which melanotically encapsulates ookinetes of many malaria species. A fully susceptible strain was also selected for comparison. The proposed research will focus on examining the biochemical and genetic basis for resistance. A newly-discovered model system of resistance that uses ion exchange beads will be used for genetic and biochemical studies. Plasmodium- resistant mosquitoes melanize negatively charged C-25 beads while susceptible mosquitoes do not. This system will greatly facilitate quantitative trait loci mapping of resistance genes, since no parasites need to be introduced and males can be scored. Markers to be used for mapping include an esterase locus which has been shown to be associated with resistance and microsatellite markers. A total of 137 microsatellite markers are now available from all autosomes and the X-chromosome. In addition to these mapping studies, the biochemistry of melanization in resistant mosquitoes and the lack of melanization in susceptible mosquitoes will also be examined. C-25 beads inoculated into susceptible mosquitoes and then dissected and introduced into resistant mosquitoes are not melanized. The nature of this protection will be studied by treatment of the beads with various enzymes prior to inoculation into resistant mosquitoes. SDS PAGE will be used to examine proteins on several types of beads destined to be melanized in the resistant strain and on unmelanized beads in the susceptible strain. Proteins associated with melanization or with the protective response in susceptible mosquitoes will be purified and used for polyclonal antibody production.