ANTISPOROZOITE ANTIBODIES WITH PROTECTIVE AND NONPROTECTIVE ACTIVITIES - IN-VITRO AND IN-VIVO CORRELATIONS USING PLASMODIUM-GALLINACEUM, ANAVIAN MODEL

A correlation was observed between in vivo and in vitro activity of si x monoclonal antibodies (mAb) against the major circumsporozoite prote in of the avian malaria Plasmodium gallinaecum as follows. (1) Two mAb were protective, totally abrogating sporozoite infectivity to chicks, its natural host, in vivo; they caused 100% inhibition of sporozoite invasion (ISI) in vitro to SL-29 chicken fibroblasts and intense ISI t o cultured chicken macrophages, as well as inhibited the exoerythrocyt ic development of sporozoites taken up by macrophages, the initial cel l host of P. gallinaceum sporozoites. (2) Two mAb were partially prote ctive in that they reduced sporozoite infectivity to chicks, caused pa rtial ISI to SL-29 and macrophage cells and partial inhibition to the exoerythrocytic development of sporozoites in macrophages in vitro. (3 ) Two mAb were totally inactive in vivo although they both bound to th e sporozoite antigens as detected by indirect immunofluorescence, west ern blot, and ELISA; they both failed to induce ISI or inhibit the exo erythrocytic development in macrophages. The possible participation of macrophages as the initial cell type involved in sporozoite destructi on in the presence of anti-circumsporozoite antibodies is discussed.