The distribution of circumsporozoite protein (CS) in Anopheles stephensi mosquitoes infected with Plasmodium falciparum malaria.

We monitored the distribution of Plasmodium falciparum circumsporozoite protein (CS) in Anopheles stephensi using an immunohistochemical method. An alkaline phosphatase-labeled monoclonal antibody, specific for the CS protein of P. falciparum, was incubated with tissue sections from infected and non-infected mosquitoes. Sections were stained for phosphatase activity using a new fuchsin/naphthol AS-BI phosphate capture system. Distribution of the CS protein in mosquitoes was dependent on the time after post-infective blood meal. CS protein was first detected in immature oocysts on the mosquito midgut. As oocysts differentiated to mature sporoblasts, detectable CS protein increased. Between 11-16 days post infective blood meal, CS protein was detected on the surface of sporozoites that were released into the hemolymph from oocysts. Although sporozoites were found throughout the hemocoel, they were most frequently associated with the salivary glands and flight muscle. Once in the salivary glands, sporozoites massed into bundles. The amount of CS protein associated with bundles of sporozoites was highly variable.