A carboxyl-terminal fragment of Plasmodium falciparum gp195 expressed by a recombinant baculovirus induces antibodies that completely inhibit parasite growth.
The major merozoite surface Ag (gp195) of Plasmodium falciparum has been shown to protect monkeys against parasite infection, and gp195-based synthetic peptides and recombinant polypeptides have been evaluated as potential malaria vaccines. A major problem in developing a gp195-based recombinant vaccine has been the difficulty in obtaining a recombinant polypeptide that is immunologically equivalent to the native protein. In this study, the carboxyl-terminal processing fragment (p42) of gp195 was produced in yeast and in a baculovirus recombinant system. Immunologic analyses indicated that the secreted baculovirus p42 (BVp42) expressed native, disulfide-dependent conformational epitopes, whereas these epitopes were poorly represented in the intracellular yeast p42. BVp42, but not yeast p42, was also recognized by the majority of gp195-specific antibodies of animals immunized with purified native gp195, indicating that the anti-gp195 response of these animals was focused on conformational determinants of the p42 processing fragment. Sera against native gp195 of congenic mice of diverse H-2 haplotypes recognized the BVp42 polypeptide, demonstrating that a genetically heterogeneous population is capable of responding to p42 epitopes. BVp42 was highly immunogenic and induced high titers of antibodies that were cross-reactive with purified native gp195 in an ELISA and also reacted with schizonts and merozoites by immunofluorescence. Anti-BVp42 antibodies completely inhibited the in vitro growth of the malaria parasite, whereas anti-yeast p42 antibodies had no effect. These results indicate that native, conformational epitopes of p42 are critical for the induction of gp195-specific, parasite growth-inhibitory antibodies and that the BVp42 polypeptide efficiently induces antibodies specific for these native determinants.
Chang
S P
SP
Department of Tropical Medicine and Medical Microbiology, John A. Burns School of Medicine, University of Hawaii, Honolulu 96816.
Gibson
H L
HL
Lee-Ng
C T
CT
Barr
P J
PJ
Hui
G S
GS
D000818:Animals; D000913:Antibodies, Protozoan / Q000032:analysis*; D016367:Baculoviridae / Q000235:genetics / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D007114:Immunization; D051379:Mice; D008810:Mice, Inbred C57BL; D010446:Peptide Fragments / Q000276:immunology*; D010963:Plasmodium falciparum / Q000254:growth & development / Q000276:immunology*; D015800:Protozoan Proteins / Q000276:immunology*; D016052:Protozoan Vaccines / Q000276:immunology; D011817:Rabbits; D011995:Recombination, Genetic
D000913:Antibodies, Protozoan; D010446:Peptide Fragments; D015800:Protozoan Proteins; D016052:Protozoan Vaccines