Novel anti-vector immune strategies that target the midgut of Anopheles gambiae mosquitoes

In light of insecticide resistance in vectors and environmental concerns over pesticides, immunological killing of vectors by way of host vaccination with vector antigens has been developed as an alternative vector-borne disease control method. Although this method has proven somewhat successful in ticks, there has been little success in identifying anti-mosquito vaccine antigens. I have identified a number of problems with past anti-mosquito immunization efforts and have applied novel molecular immune strategies to circumvent these problems as well as to elucidate the mediators and the targets involved in anti-mosquito immunity. The aims of this dissertation were threefold. (1) To study and to replicate traditional methods used in generating antimosquito immunity. I identified a possible mosquito midgut-antigen target using previously produced mosquitocidal sera but immunization of rabbits with this semipurified antigen failed to elicit a mosquitocidal immune response. Further immunizations with different preparations of Anopheles gambiae midgut antigens generated significant and specific antibody production, but failed to kill mosquitoes. These data highlighted the difficulty in replicating and dissecting mosquitocidal immunity by traditional midgut protein vaccination. (2) To pan a phage-displayed library of antibody fragments (scFv) on An. gambiae midgut antigens in order to select for midgut-binding scFv clones, and to test these clones for mosquitocidal activity. The methods I used resulted in the identification of a midgut carbohydrate-specific scFv that had no effect on mosquito survival. Although my results suggest that multiple midgut-binding scFv can be selected with slight modifications in selection procedure. (3) To immunize mice with mosquito midgut cDNA, characterize the resulting immune profiles, and test whether they can affect mosquito survival or fecundity. Immunization with midgut cDNA stimulated an immune response that was highly lethal to mosquitoes, but was characterized by weak humoral immunity. A midgut protein boost stimulated a shift to Type II immunity which abrogated the killing effect, but caused a decrease in egg production. These results suggest that mosquito death was primarily due to a cellular immune response against mosquito midgut antigens in vivo. Ultimately, the strategies I employed will help to elucidate mosquito-host immune interactions and will help to discover critical mosquito antigens.