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 potential vaccine candidate against erythrocytic stages of malaria. We report, for the first time, the immunological characteristics of recombinant ABRA constructs. 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 chromatography. 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 the protein. More importantly, the purified immunoglobulin G specific to middle and C-terminal fragments prevented parasite growth at levels approaching 80-90%. We found that these proteins were also recognized by sera from P. falciparum-infected patients from Rourkela, a malaria endemic zone of India. Our immunogenicity results suggest that potential of ABRA as a vaccine candidate antigen should be investigated further.