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

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 geographical Plasmodium falciparum isolates. To explore whether the sequence heterogeneity of PfMSP-1 leads to variation in naturally acquired anti-MSP-119 antibodies, the present study was undertaken to study PfMSP-119 sequence polymorphism in malaria-endemic villages in eastern India and also carried out a competition enzyme-linked immunosorbent assay using three PfMSP-119 variant forms.

Methods: The sequence variations in the C-terminal region of PfMSP-119 were determined in a malaria endemic region. Three PfMSP-119 variants were produced in Escherichia 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-119 variant forms were isolated in a singe geographical location. Three of PfMSP-119 variant forms when expressed in E. coli showed 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 in P. falciparum-infected patient sera, however their role in protection requires further investigation. These results thereby, suggest the importance of a multi-allelic PfMSP-119 based vaccine for an effective malaria control.

Figure 1

Sequence diversity in the C-terminal region (blocks 16 and 17) of MSP-1 in Indian P. falciparum isolates in a single geographical location.

Figure 2

Expression and immunoblot analysis of E. coli expressed PfMSP-1₁₉ variants. (a) Coomassie blue-stained 12% SDS-polyacrylamide gel of purified PfMSP-1₁₉ variants. (b & c) Immunoblot analysis to show the reactivity of PfMSP-1₁₉ variants with monoclonal antibodies (12.10) and with anti-PfMSP1₁₉ (Q-KNG-L) antibody.

Figure 3

Reactivity of PfMSP-1₁₉ variants in an ELISA with sera collected from P. falciparum infected patients at a dilution of 1:200. Error bars indicate S.D.

Figure 4

Immunodepletion assay showing the presence of PfMSP1₁₉ allele specific antibodies in sera from P. falciparum infected patients. Error bars indicate S.D.