Identification of circumsporozoite proteins in individual malaria-infected mosquitoes by western blot analysis.

Circumsporozoite (CS) proteins of rodent (Plasmodium berghei), simian (P. knowlesi), and human (P. falciparum) malaria parasites extracted from dead and dried mosquitoes have been identified by the Western blot (immunoblot) technique. Dried mosquitoes which were laboratory-reared and infected with Plasmodium or freshly dissected sporozoites were triturated in sample reducing buffer and the extracts electrophoresed in a 10% SDS-polyacrylamide gel. After transferring the proteins to nitrocellulose, the molecular weights of both precursor and surface CS proteins of the plasmodial species were identified by probing with homologous monoclonal antibodies followed by 125I-labeled anti-mouse IgG. The molecular weights of the CS proteins extracted from dried mosquitoes were identical to those of CS proteins extracted from viable sporozoites. Immunoblot analysis is sensitive in that it can detect as few as 100 sporozoites. This technique is of epidemiological significance because it permits the identification of CS proteins of different plasmodial isolates extracted from individual, dried field-collected mosquitoes.