Studies on immune responses in Plasmodium-melanizing and -nonmelanizing strains of Anopheles gambiae

The traditional malaria control strategies are not universally efficient because of increasing drug or insecticide resistance. One possible new control method is the replacement of natural vector populations by genetically engineered mosquitoes which can not transmit malaria parasites. Completely refractory and completely susceptible strains of Anopheles gambiae were genetically selected. Malaria parasites are melanotically encapsulated in the refractory strain but not in the susceptible strain. Studies comparing these two strains are valuable to understanding the molecular basis of vector competence for malaria.; Negatively charged (CM-25) Sephadex beads were encapsulated much better in refractory mosquitoes than in susceptible mosquitoes. Female mosquito age and reproductive status strongly affected the ability to melanize beads. The efficiency of bead melanization was the highest in both strains on the day immediately following eclosion (Day 0), thereafter the efficiency increased steadily until the last time point, on Day 7. The level of melanization of beads increased after blood feeding in refractory but not in susceptible mosquitoes.; Hemolymph polypeptides from Plasmodium-refractory and -susceptible strains of An. gambiae were compared by one- and two-dimensional gel electrophoresis. One of the refractory-specific spots was sequenced and identified as AgSp14D1, an An. gambiae infection responsive serine protease that is most similar to the Drosophila gene easter and Manduca prophenoloxidase activating enzyme. This gene maps to division 14D on the polytene chromosomes which has been associated with the melanization phenotype by quantitative trait loci mapping.; Phenoloxidase (PO) activity was compared in the hemolymph of Plasmodium-refractory and -susceptible strains of An. gambiae. The differences between strains in the effect of mosquitoe age and reproductive status on DPO activity were not significantly differently stastically except on day 2 after blood feeding. Few differences in the behavior of DPO between two strains were found supporting the idea that activators or regulators of the melanization cascade are more likely to be responsible for the differences between the refractory and susceptible stranis.; Identification of the molecular basis for melanotic encapsulation of malaria parasite is an important goal in vector biology. My studies may contribute for further investigation of the biochemical and genetic basis for parasite melanization.