Abstract
The mosquito midgut is the organ into which the blood meal passes and in which, within a peritrophic membrane secreted by the epithelium, the blood is retained during digestion and absorption. The mosquito midgut is lined with an actin filled microvilli that are exposed to the harsh environment of the gut lumen such as food particle abrasion, digestive hydrolases and attack by pathogens and parasites that are taken in by the blood meal. These microvilli are protected them these effects by the peritrophic matrix, the glycocalyx and the mucin proteins that line their epithelial surfaces. Immunization of BALB/c mice with AgMUC1/IL-12 cDNA has been shown to kill mosquitoes when fed on these mice. Mucin is one of the proteins produced in the mosquito midgut after a blood meal. The fine structure of the mosquito midgut epithelium interacting with immune factors such as antibodies or immune cells is of special significance for interpreting early events in the interaction between the mosquito midgut lining and the specific immune components present in the blood of AgMUC1/IL-12 cDNA immunized BALB/c mice. Following bright light microscopy, scanning electron and transmission electron microscopic observations of the features seen in mosquito midgut sections from An. gambiae mosquitoes fed on BALB/c mice immunized with AgMUC1/IL-12 cDNA, the most likely immune mechanisms responsible for mosquito killing could be cell mediated, most likely antibody dependent cellular cytotoxicity. Both necrotic and apoptotic processes that could be the cause of mosquito death were seen to take place in the cells lining the midgut epithelium.
