Characterization of Plasmodium interspersed repeats (PIR) in Plasmodium knowlesi

Abstract

Plasmodium knowlesi, the leading cause of Malaria in Southeast Asia utilizes variant surface antigens encoded by multigene families to evade host immune response. The Plasmodium Interspersed Repeats (PIR) family is predicted to contribute to antigenic variation, but there is no direct evidence of their functions. In P. knowlesi, the Knowlesi Interspersed Repeats (KIRs) are predicted to exhibit host CD99 mimicry, which can potentially interrupt the host immune response. This study aims to identify the localization of KIR proteins and predict their immuno-modulatory roles. Selected KIR members, predicted to have unique localization and CD99-like regions, were expressed in P.knowlesi with episomal plasmids. Immunofluorescence assays and western blot were performed to determine protein localization and size. All analyzed KIR proteins were exported into the infected red blood cell cytoplasm, supporting their potential role in antigenic variation. However, the observed molecular weights differed from predictions, suggesting potential post-translational modifications, signal peptide cleavage, or membrane integration. CD99-mimicry by KIRs could offer advantages, potentially affecting apoptosis of T cells, cytoadherence and protein trafficking. Future studies using phagocytosis assays and investigations into protein modifications and export pathways can be conducted to elucidate the impact of KIRs on host immune response.