Allelic forms of gp195, a major blood-stage antigen of Plasmodium falciparum, are expressed in liver stages

Mature exoerythrocytic (EE) forms of two cloned lines (3D7 and HB3) of Plasmodium falciparum were obtained in the livers of splenectomized chimpanzees. Sectioned preparations were examined by immunofluorescence (IFA) using mAbs that distinguished allelic variants of the blood-form antigen gp195 and mAbs that recognized multiple conserved epitopes of gp195. EE forms and blood schizonts exhibited identical IFA reactions for each respective clone, showing that the antigen was expressed identically in liver and blood-stage parasites. A third chimpanzee was infected with sporozoites derived from a mixture of 3D7 and HB3 gametocytes that had undergone cross-fertilization in the mosquitoes. IFAs on the EE forms in this animal showed that segregation of each gp195 allele had occurred earlier in the life cycle, providing evidence that the parasite is haploid for the whole of its mammalian development.