Résumé
Immunological cross-reactivity studies between the Apicomplexa
Babesia divergens and
Plasmodium falciparum allowed usto identify a
P falciparum 60 kDa protein (Pf60) using an antiserum directed against a
B divergens 37 kDa culture-derived exoantigen. In immunofluorescence assays (IFA), Pf60 appears as a doublet of fluorescent spots associated to the apical pole of merozoites. The doublet co-locates with two rhoptry components: the protein RAP-1 and the 140/130/110 (105) kDa rhoptry protein complex suggesting the rhoptry location of Pf60. The biosynthesis of Pf60, established by labeling experiments with [
35S]methionine on synchronized cultures, and by immunofluorescence detection, occurred during late schizogony. The physico-chemical properties of Pf60, the absence of identified precursor forms and the absence of co-precipitation with other proteins indicated a new class of rhoptry protein. Pf60 was detected in all the different geographic
P falciparum strains so far tested, with a slight variability in molecular mass ranging from 58 to 60 kDa. During the invasion process of erythrocytes by merozoites, the IFA showed the presence of the Pf60 in the apex of free merozoites, but not in invading merozoite, as well as in new ring-infected erythrocytes. Furthermore, immunoprecipitation assays indicated the presence of Pf60 in the culture medium, and its absence in new ring-infected erythrocytes. All together these results suggest a possible involvement of the Pf60 protein in the invasion process.