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  1. Fulltext In vitro invasion inhibition assay using antibodies against Plasmodium knowlesi Duffy binding protein alpha and apical membrane antigen protein 1 in human erythrocyte-adapted P. knowlesi A1-H.1 strain
    Muh F, Lee SK, Hoque MR, Han JH, Park JH, Firdaus ER, et al.
    Malar J, 2018 Jul 27;17(1):272.
    PMID: 30049277 DOI: 10.1186/s12936-018-2420-4
    BACKGROUND: The rapid process of malaria erythrocyte invasion involves ligand-receptor interactions. Inducing antibodies against specific ligands or receptors that abrogate the invasion process is a key challenge for blood stage vaccine development. However, few candidates were reported and remain to be validated for the discovery of new vaccine candidates in Plasmodium knowlesi.

    METHODS: In order to investigate the efficacy of pre-clinical vaccine candidates in P. knowlesi-infected human cases, this study describes an in vitro invasion inhibition assay, using a P. knowlesi strain adapted to in vitro growth in human erythrocytes, PkA1-H.1. Recombinant proteins of P. knowlesi Duffy binding protein alpha (PkDBPα) and apical membrane antigen 1 (PkAMA1) were produced in Escherichia coli system and rabbit antibodies were generated from immune animals.

    RESULTS: PkDBPα and PkAMA1 recombinant proteins were expressed as insoluble and produced as a functional refolded form for this study. Antibodies against PkDBPα and PkAMA1 specifically recognized recombinant proteins and native parasite proteins in schizont-stage parasites on the merozoite organelles. Single and combination of anti-PkDBPα and anti-PkAMA1 antibodies elicited strong growth inhibitory effects on the parasite in concentration-dependent manner. Meanwhile, IgG prevalence of PkDBPα and PkAMA1 were observed in 13.0 and 46.7% in human clinical patients, respectively.

    CONCLUSION: These data provide support for the validation of in vitro growth inhibition assay using antibodies of DBPα and AMA1 in human-adapted P. knowlesi parasite PkA1-H.1 strain.

    Matched MeSH terms: Receptors, Cell Surface/immunology*
  2. Fulltext Two Genetically Distinct Plasmodium knowlesi Duffy Binding Protein Alpha Region II (PkDBPαII) Haplotypes Demonstrate Higher Binding Level to Fy(a+b+) Erythrocytes than Fy(a+b--) Erythrocytes
    Liew CC, Lau YL, Fong MY, Cheong FW
    Am J Trop Med Hyg, 2020 05;102(5):1068-1071.
    PMID: 32189613 DOI: 10.4269/ajtmh.19-0836
    Invasion of human erythrocytes by merozoites of Plasmodium knowlesi involves interaction between the P. knowlesi Duffy binding protein alpha region II (PkDBPαII) and Duffy antigen receptor for chemokines (DARCs) on the erythrocytes. Information is scarce on the binding level of PkDBPαII to different Duffy antigens, Fya and Fyb. This study aims to measure the binding level of two genetically distinct PkDBPαII haplotypes to Fy(a+b-) and Fy(a+b+) human erythrocytes using erythrocyte-binding assay. The binding level of PkDBPαII of Peninsular Malaysian and Malaysian Borneon haplotypes to erythrocytes was determined by counting the number of rosettes formed in the assay. Overall, the Peninsular Malaysian haplotype displayed higher binding activity than the Malaysian Borneon haplotype. Both haplotypes exhibit the same preference to Fy(a+b+) compared with Fy(a+b-), hence justifying the vital role of Fyb in the binding to PkDBPαII. Further studies are needed to investigate the P. knowlesi susceptibility on individuals with different Duffy blood groups.
    Matched MeSH terms: Receptors, Cell Surface/immunology
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