Characterization of one polypeptide antigen potentially related to protective immunity against the blood infection by Plasmodium falciparum in the squirrel monkey.

We have previously demonstrated that squirrel monkeys vaccinated with a particular protein fraction of Plasmodium falciparum develop a protective immunity that is expressed at the humoral level by the presence of antibodies directed essentially against two parasite proteins. We have now isolated a mAb that recognizes one of these polypeptides of an apparent m.w. of 90,000 and an isoelectric point of 6.2. This parasite protein is synthesized in a short period of the asexual blood cycle corresponding to the mature tropho and early schizont stages, but is stable up to the end of the schizogony. By immunofluorescence analysis, the protein seems to be located essentially at the surface of the parasite and/or in the parasitophorous vacuole. The protein is degraded or modified in the process of reinvasion, because it was not detected in merozoites or in newly invaded RBC. Monoclonal antibody XIV-7 has no inhibitory effect against the parasite in vitro.