Plasmodium falciparum: gp195 tripeptide repeat-specific monoclonal antibody inhibits parasite growth in vitro

Seven monoclonal antibodies (mAbs) were produced to the precursor of the merozoite surface antigens (MSA-1 or gp195) using the Plasmodium falciparum Uganda-Palo Alto isolate. Three mAbs (CE2, DB8, and EB2) reacted with epitopes on the 83-kDa N-terminal processing fragment by immunoprecipitation of radiolabeled proteins and in immunoblots of native and recombinant proteins. Three other mAbs (BC9, AG5, and AD9) reacted with epitopes on the 42- and 19-kDa C-terminal processing fragments while one remaining mAb (24A1.7) reacted with only 150- and 110-kDa intermediate processing fragments. Epitopes were mapped to either conserved or dimorphic regions of the expressed protein when parasite isolates with known MSA-1 alleles were examined by indirect immunofluorescence. Moreover, one mAb (CE2), specific for the variable tripeptide repeat region SAQ(SGT)5, was growth inhibitory for P. falciparum in vitro. Growth inhibition by the mAb was concentration dependent and its parasite-neutralizing properties were not enhanced when used in combination with other gp195-specific mAbs. These results may be useful in the elucidation of biological variation of field isolates and in the definition of immunologically relevant epitopes in a gp195-based malaria vaccine.