The structure of Plasmodium yoelii merozoite surface protein 119, antibody specificity and implications for malaria vaccine design

Inhibition of parasite invasion by monoclonal antibody against epidermal growth factor-like domain of Plasmodium vivax merozoite surface protein 1 paralog

The Plasmodium vivax merozoite surface protein 1 paralog (PvMSP1P), which has epidermal growth factor (EGF)-like domains, was identified as a novel erythrocyte adhesive molecule. This EGF-like domain (PvMSP1P-19) elicited high level of acquired immune response in patients. Antibodies against PvMSP1P significantly reduced erythrocyte adhesion activity to its unknown receptor. To determine PvMSP1P-19-specific antibody function and B-cell epitopes in vivax patients, five monoclonal antibodies (mAbs) and 18-mer peptides were generated. The mAb functions were determined by erythrocyte-binding inhibition assay and invasion inhibition assay with P. knowlesi. B-cell epitopes of PvMSP1P-19 domains were evaluated by peptide microarray. The pvmsp1p-19 sequences showed limited polymorphism in P. vivax worldwide isolates. The 1BH9-A10 showed erythrocyte binding inhibitory by interaction with the N-terminus of PvMSP1P-19, while this mAb failed to recognize PkMSP1P-19 suggesting the species-specific for P. vivax. Other mAbs showed cross-reactivity with PkMSP1P-19. Among them, the 2AF4-A2 and 2AF4-A6 mAb significantly reduced parasite invasion through C-terminal recognition. The linear B-cell epitope in naturally exposed P. vivax patient was identified at three linear epitopes. In this study, PvMSP1P-19 N-terminal-specific 1BH9-A10 and C-terminal-specific 2AF4 mAbs showed functional activity for epitope recognition suggesting that PvMSP1P may be useful for vaccine development strategy for specific single epitope to prevent P. vivax invasion.

The production of SPusp45-MSP-1₁₉ gene construct and its recombinant protein in <em>Lactococcus lactis</em> to be used as a malaria vaccine

Background: Merozoite surface protein 1 (MSP-1) is a major protein used by the Plasmodium during red blood cells invasion in malaria. MSP-119, one of MSP-1 is highly conserved, and  it is a potential malaria vaccine candidate because the monoclonal antibodies are capable blocking erythrocyte invasion in vitro. The aim of this study was to produce MSP-119 gene construct and the recombinant protein in Lactococcus lactis.Methods: Usp45-MSP-119, derived from codon optimization and the synthetic gene, was inserted into the pMAT cloning vector. A vector expressing MSP-119 included usp45 has been constructed by the manipulation of recombinant DNA using restriction enzymes. The MSP-119 protein was expressed to 45% ammonium sulfate precipitation and purified using Sephadex-G50 gel filtration chromatography. The expressed protein was characterized by SDS-PAGE and dot blot.Results: usp45-MSP-119 gene was amplified using specific primers and inserted into the multiple cloning sites in the expression vector pNZ8148 with size 3,538 bp as a recombinant vector. The protein of  MSP-119 was successfully expressed in L. lactis with molecular weight of 10.45 kDa. The dot blot was tested in 3 different comparisons between the host cells, non-induced cells, and induced cells with 10 ng/ml nisin. The results showed that 10 ng/ml nisin gave a positive reaction as detected by dot blot assay.Conclusion: This study confirmed that the usp45-MSP-119 gene was successfully inserted into the multiple cloning sites of the pNZ8148 expression vector and the MSP-119 protein expressed in the NICE system of the L. lactis host cell.

Isolation and Characterization of Vaccine Candidate Genes Including CSP and MSP1 in Plasmodium yoelii

Malaria is an infectious disease affecting humans, which is transmitted by the bite of Anopheles mosquitoes harboring sporozoites of parasitic protozoans belonging to the genus Plasmodium. Despite past achievements to control the protozoan disease, malaria still remains a significant health threat up to now. In this study, we cloned and characterized the full-unit Plasmodium yoelii genes encoding merozoite surface protein 1 (MSP1), circumsporozoite protein (CSP), and Duffy-binding protein (DBP), each of which can be applied for investigations to obtain potent protective vaccines in the rodent malaria model, due to their specific expression patterns during the parasite life cycle. Recombinant fragments corresponding to the middle and C-terminal regions of PyMSP1 and PyCSP, respectively, displayed strong reactivity against P. yoelii-infected mice sera. Specific native antigens invoking strong humoral immune response during the primary and secondary infections of P. yoelii were also abundantly detected in experimental ICR mice. The low or negligible parasitemia observed in the secondary infected mice was likely to result from the neutralizing action of the protective antibodies. Identification of these antigenic proteins might provide the necessary information and means to characterize additional vaccine candidate antigens, selected solely on their ability to produce the protective antibodies.