Immunogenicity of recombinant fragments of Plasmodium falciparum acidic basic repeat antigen produced in Escherichia coli

The acidic basic repeat antigen (ABRA) of Plasmodium falciparum is a potent ial vaccine candidate against erythrocytic stages of malaria. We report, fo r the first time, the immunological characteristics of recombinant ABRA con structs. The recombinant proteins representing different fragments of ABRA were expressed in Escherichia coli, either as fusions with maltose binding protein or as 6X histidine tagged molecules, and purified by affinity chrom atography. Immunogenicity studies with these constructs in rabbits and mice indicated that the N-terminal region is the least immunogenic part of ABRA . T-cell proliferation experiments in mice immunized with these constructs revealed that the T-cell epitopes were localized in the middle portion of t he protein. More importantly, the purified immunoglobulin G specific to mid dle and C-terminal fragments prevented parasite growth at levels approachin g 80-90%. We found that these proteins were also recognized by sera from P. falciparum-infected patients from Rourkela, a malaria endemic zone of Indi a. Our immunogenicity results suggest that potential of ABRA as a vaccine c andidate antigen should be investigated further.