Plasmodium knowlesi Duffy binding protein alpha region II (PkDBP alpha II) in clinical isolates from Peninsular Malaysia and Malaysian Borneo exhibit different immune responses in animal models

• Main Authors: Azlan, Ummi Kalthum, Cheong, Fei Wen, Lau, Yee Ling, Fong, Mun Yik
• Format: Article
• Published: Springer Verlag (Germany) 2022
• Subjects: R Medicine
• Online Access: http://eprints.um.edu.my/40885/
• Institution: Universiti Malaya

Plasmodium knowlesi utilizes the Duffy binding protein alpha (PkDBP alpha) to facilitate its invasion into human erythrocytes. PkDBP alpha region II (PkDBP alpha II) from Peninsular Malaysia and Malaysian Borneo has been shown to occur as distinct haplotypes, and the predominant haplotypes from these geographical areas demonstrated differences in binding activity to human erythrocytes in erythrocyte binding assays. This study aimed to determine the effects of genetic polymorphisms in PkDBP alpha II to immune responses in animal models. The recombinant PkDBP alpha II (similar to 45 kDa) of Peninsular Malaysia (PkDBP alpha II-H) and Malaysian Borneo (PkDBP alpha II-S) were expressed in a bacterial expression system, purified, and used in mice and rabbit immunization. The profile of cytokines IL-1ra, IL-2, IL-6, IL-10, TNF-alpha, and IFN-gamma in immunized mice spleen was determined via ELISA. The titer and IgG subtype distribution of raised antibodies was characterized. Immunized rabbit sera were purified and used to perform an in vitro merozoite invasion inhibition assay. The PkDBP alpha II-immunized mice sera of both groups showed high antibody titer and a similar IgG subtype distribution pattern: IgG2b > IgG1 > IgG2a > IgG3. The PkDBP alpha II-H group was shown to have higher IL-1ra (P = 0.141) and IL-6 (P = 0.049) concentrations, with IL-6 levels significantly higher than that of the PkDBP alpha II-S group (P <= 0.05). Merozoite invasion inhibition assay using purified anti-PkDBP alpha II antibodies showed a significantly higher inhibition rate in the PkDBP alpha II-H group than the PkDBP alpha II-S group (P <= 0.05). Besides, anti-PkDBP alpha II-H antibodies were able to exhibit inhibition activity at a lower concentration than anti-PkDBP alpha II-S antibodies. PkDBP alpha II was shown to be immunogenic, and the PkDBP alpha II haplotype from Peninsular Malaysia exhibited higher responses in cytokines IL-1ra and IL-6, antibody IgM level, and merozoite invasion inhibition assay than the Malaysian Borneo haplotype. This suggests that polymorphisms in the PkDBP alpha II affect the level of immune responses in the host.