Polymorphism and epitope sharing between the alleles of merozoite surface protein-1 of Plasmodium falciparum among Indian isolates

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Abstract
Background: The C-terminal region of merozoite surface protein-1 (MSP-1) is one of the leading candidates for vaccination against the erythrocytic stages of malaria. However, a major concern in the development of MSP-1 based malaria vaccine is the polymorphism observed in different geographicalPlasmodium falciparumisolates. To explore whether the sequence heterogeneity of PfMSP-1 leads to variation in naturally acquired anti-MSP-119antibodies, the present study was undertaken to study PfMSP-119sequence polymorphism in malaria-endemic villages in eastern India and also carried out a competition enzyme-linked immunosorbent assay using three PfMSP-119variant forms.Methods: The sequence variations in the C-terminal region of PfMSP-119were determined in a malaria endemic region. Three PfMSP-119variants were produced inEscherichia coli(PfMSP119QKNG-L, PfMSP119EKNG-L and PfMSP119ETSR-F) and an immunodepletion assay was carried out using the corresponding patients' sera.Results: Results revealed predominance of PfMAD20 allele among Indian field isolates. Seven PfMSP-119variant forms were isolated in a singe geographical location. Three of PfMSP-119variant forms when expressed inE. colishowed presence of cross-reaction as well as variant specific antibodies in malaria infected patient sera.Conclusion: The present study demonstrates the existence of allele specific antibodies inP. falciparum-infected patient sera, however their role in protection requires further investigation. These results thereby, suggest the importance of a multi-allelic PfMSP-119based vaccine for an effective malaria control.