Analyses of the transcriptome profiles of Plasmodium falciparum infected erythrocytes selected for binding to the human endothelial receptors (ICAM-1, P-selectin, E-selectin, CD9 and CD151)

Abstract

P. falciparum is responsible for most of the morbidity and mortality accompanying malaria infections in humans. This is attributed to the ability of this parasite to evade the immune system and to sequester in small blood vessels of vital organs within its human host. This sequestration leads to serious life threatening complications, such as cerebral malaria, especially in children younger than five years of age. Cytoadhesion, that is required for sequestration, depends on the interaction between a human endothelial receptor and a matching parasite ligand. Until now, a panel of receptors (22 receptors) have been identified to interact with P. falciparum infected erythrocytes (IEs). The parasiteʼs interactions to only four host receptors (CD36, ICAM-1, CSA and EPCR) were studied in detail, The main parasite ligand responsible for the cytoadhesion of mature trophozoites is the so-called PfEMP1, which is encoded by the var multigene family. var genes are mutually exclusively expressed and the parasite can switch expression between the about 60 copies present in its genome. The corresponding mutually expressed var gene is decisive for the parasiteʼs tropsim to the endothelial cells. The enormous diversity of PfEMP1 domain structures makes it difficult to identify the binding domains for every receptor. This study aimed to analyse the transcriptome profile of the parasites that are able to bind to one out of these five different endothelial receptors (ICAM-1, P-selectin, E-selectin, CD9 and CD151) as a first step to identify their PfEMP1´s ligands. In order to achieve this aim, IEs were enriched by binding to the corresponding receptor for several rounds. The illumina NGS platform was used for mRNA sequencing and finally gene differential analysis was performed using a generalized lineal model via the DEseq Bioconductor package. The results confirmed the known ligands of ICAM-1. Two interesting group A var candidates were identified to be differentially expressed in the parasite population enriched by binding to P-selectin (IT4_var02/07). Upon enrichment over CD9, eight var genes were differentially expressed; with four of them being group A var genes (IT4_var02/64/09/07). No peremptory ligand was identified for both E-selectin and CD151. In conclusion, this study anticipated P-selectin and CD9 interactions with PfEMP1sʼ ligands as a new way to reveal more details about the exact mechanisms underlying cerebral malaria. These need more efforts to be investigated for further studies to exactly characterize the binding domain(s) and finally to develop an inhibitory mechanism.