Immunogenicity of bacterial-expressed recombinant Plasmodium knowlesi merozoite surface protein-1(42) (MSP-1(42))

BACKGROUND: Plasmodium knowlesi is the fifth Plasmodium species that can infect humans. The Plasmodium merozoite surface protein-1(42) (MSP-1(42)) is a potential candidate for malaria vaccine. However, limited studies have focused on P. knowlesi MSP-1(42). METHODS: A ~42 kDa recombinant P. knowlesi MSP-1(42) (pkMSP-1(42)) was expressed using an Escherichia coli system. The purified pkMSP-1(42) was evaluated with malaria and non-malaria human patient sera (n = 189) using Western blots and ELISA. The immunogenicity of pkMSP-1(42) was evaluated in mouse model. RESULTS: The purified pkMSP-1(42) had a sensitivity of 91.0% for detection of human malaria in both assays. Specificity was 97.5 and 92.6% in Western blots and ELISA, respectively. Levels of cytokine interferon-gamma, interleukin-2, interleukin-4, and interleukin-10 significantly increased in pkMSP-1(42)-immunized mice as compared to the negative control mice. pkMSP-1(42)-raised antibody had high endpoint titres, and the IgG isotype distribution was IgG1 > IgG2b > IgG3 > IgG2a. CONCLUSIONS: pkMSP-1(42) was highly immunogenic and able to detect human malaria. Hence, pkMSP-1(42) would be a useful candidate for malaria vaccine development and seroprevalence studies.