PLASMODIUM-FALCIPARUM - DIFFERENTIAL PARASITE GROWTH-INHIBITION MEDIATED BY ANTIBODIES TO THE ANTIGENS PF332 AND PF155 RESA/

Plasmodium falciparum-reactive antibodies can inhibit growth of parasi te blood stages in vitro by interfering at different stages of parasit e development. Antibodies reactive with repeat sequences in Pf155/ring -infected surface antigen (Pf155/RESA) or in antigen Pf332 inhibit par asite growth as determined by a reduction of newly infected erythrocyt es. Antibodies to Pf155/RESA have been implicated in merozoite invasio n inhibition. Since it was considered unlikely that antibodies to the late stage antigen Pf332 act on merozoite invasion, we investigated at what developmental stage this growth inhibition takes place. Parasite s were cultured in the presence of antibodies to repeat sequences of e ither Pf332 or Pf155/ RESA and were examined with regard to the distri bution of different stages and their morphology. As expected, antibodi es to both antigens decreased the number of ring stages after reinfect ion. They did not affect the intraerythrocytic development of ring sta ges or trophozoites. However, antibodies to Pf332 induced high levels of schizonts displaying an abnormal morphology while antibodies to Pf1 55/RESA induced considerably lower levels of degenerated schizonts. Th us, Pf332-reactive antibodies seem to interfere with the schizont deve lopment by blocking the rupture of mature schizonts or, alternatively, by interfering intraerythrocytically with late stage parasites. (C) 1 996 Academic Press, Inc.