Recombinant DBL2b-PfEMP1 of the Indonesian Plasmodium falciparum induces immune responses in Wistar rats

Abstract

Objectives: The Duffy binding-like (DBL) domain of the Plasmodium falciparum Erythrocyte Membrane Protein 1 (PfEMP1) is reportedly responsible for the pathophysiology of cerebral malaria. People living in endemic malaria areas possess specific antibodies against PfEMP1 and elicit immune responses to control the severity of malaria infection. Therefore, PfEMP1 may be a potential protein-based vaccine candidate. This study aimed to explore the humoral and cellular immune responses induced by the recombinant DBL2b-PfEMP1 obtained from the Indonesian P. falciparum isolate. Methods: The recombinant protein was expressed in Escherichia coli BL21(DE3) as soluble and insoluble fractions, and this protein was purified using affinity chromatography before administration as a subcutaneous injection in Wistar rats on days 1, 21, and 42. Sera were harvested 14 days after the second and third injections to determine the titre of IgG and the concentration of CD4þ cells using the enzyme linked immunosorbent assay (ELISA). Results: The IgG titre and the CD4þ cell concentration were found to be increased after the second and third injections. The ManneWhitney test results showed a significant difference between the control and treatment groups for both the IgG and CD4þ cells (p ¼ 0.001 and p ¼ 0.000, respectively). Western blotting results indicated the presence of a specific antibody against the recombinant DBL2b-PfEMP1. Conclusions: The recombinant DBL2b-PfEMP1 of the Indonesian P. falciparum isolate could induce humoral and cellular immune responses. Further studies on IgG exerting inhibitory effects and the role of CD4þ cells and their association with other effector cells are essential to determine the efficacy of DBL2b-PfEMP1 and its potential application as a peptide-based malaria vaccine candidate.