The malaria sporozoite injected into a host by the bite of the mosquito vector initiates the parasite cycle that culminates in clinical disease. This sporozoite stage is highly antigenic, and immunization with irradiated sporozoites has prevented the development of malaria in rodent and simian hosts as well as in several human volunteers (1). Antisporozoite antibodies detectable in the sera of the immunized primate hosts appear to be associated with immune resistance.Recently, hybridoma-derived monoclonal antibodies directed against sporozoites of rodent and simian malaria were found to be protective, i.e., to abolish sporozoite infectivity both in vivo (2) and in vitro (3). 1 These antibodies react with circumsporozoite (CS) 2 proteins; that is, stage-and species-specific polypeptides that are uniformly distributed over the entire surface of the parasite and that are shed when cross-linked by antibodies (2, 4). 1The hybridoma technique was therefore used to develop monoclonal antibodies against sporozoites of P falciparum and P. vivax in an attempt to identify the protective antigens of the human pathogens for their application in a vaccine.
Materials and MethodsMice. BALB/c mice were immunized using viable and frozen sporozoites of P.falciparum or P. vivax. The P. falciparum spomzoites were of West African origin and were obtained by membrane feeding Anopheles gambiae mosquitoes on blood obtained from patients carrying P. falciparum gametoeytes. P. vivax sporozoites for immunization were obtained from Anopheles
In a previous paper (2) we identified a protective antigen (Pb44) of the surface membrane of sporozoites of Plasmodium berghei by means of a monoclonal antibody. Immunoprecipitation of extracts of mature salivary gland sporozoites, metabolically labeled with L[35S]methionine using the same monoclonal antibody, revealed three specific polypeptides: *Pb44, *Pb52, and *Pb54. Metabolically labeled *Pb44 is probably identical to the protective antigen previously identified by surface labeling. Both proteins have the same molecular weights and isoelectric points under denaturing conditions, and they share an epitope. Moreover, *Pb44 also seems to be located on the cell membrane. The results of pulse-chase experiments strongly suggest that *Pb52 is the precursor of *Pb44. The relationship between *Pb54 and the protective antigen is unknown. The three polypeptides seem to be strictly associated with only one of the developmental stage of the parasite. They were not detected in blood forms and were found in minute amounts in sporozoites from the midgut of mosquitoes. In contrast, in mature salivary gland sporozoites they constitute main products of protein synthesis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.