EXPRESSION AND SEROLOGIC ACTIVITY OF A SOLUBLE RECOMBINANT PLASMODIUM-VIVAX DUFFY BINDING-PROTEIN

Plasmodium vivax Duffy binding protein (DBP) is a conserved functional ly important, protein. P. vivax DBP is an asexual blood-stage malaria vaccine candidate because adhesion of B. vivax DBP to its erythrocyte receptor is essential for the parasite to continue development in huma n blood. Wt developed a soluble recombinant protein of P. vivax DBP (r DBP) and examined serologic activity to it in residents of a region of high endemicity. This soluble rDBP product contained the cysteine-ric h ligand domain and most of the contiguous proline-rich hydrophilic re gion. rDBP was expressed as a glutathione S-transferase (GST) fusion p rotein and was isolated from GST by thrombin treatment of the purified fusion protein bound on glutathione agarose beads. P. vivax rDBP was immunogenic in rabbits and indued antibodies that reacted with P. viva x and Plasmodium knowlesi merozoites. Human sera from adult residents of a region of Papua New Guinea where malaria is highly endemic or P. vivax-infected North American residents reacted with rDBP in an immuno blot and an enzyme-linked immunosorbent assay. The reactivity to reduc ed, denatured B. vivax rDBP and the cross-reactivity with P. knowlesi indicated the presence of immunogenic conserved linear B-cell epitopes , A more extensive serologic survey of Papua New Guinea residents show ed that antibody response to P. vivax DBP is common and increases with age, suggesting a possible boosting of the antibody response in some by repeated exposure to P. vivax. A positive humoral response to P. vi vax DBP correlated with a significantly higher response to P. vivax MS P-1(19). The natural immunogenicity of this DBP should strengthen its usefulness as a vaccine.