The ability of the parasite Plasmodium falciparum to evade the immune system and be sequestered within human small blood vessels is responsible for severe forms of malaria. The sequestration depends on the interaction between human endothelial receptors and P. falciparum erythrocyte membrane protein 1 (PfEMP1) exposed on the surface of the infected erythrocytes (IEs). In this study, the transcriptomes of parasite populations enriched for parasites that bind to human P-selectin, E-selectin, CD9 and CD151 receptors were analysed. IT4_var02 and IT4_var07 were specifically expressed in IT4 parasite populations enriched for P-selectin-binding parasites; eight var genes (IT4_var02/07/09/13/17/41/44/64) were specifically expressed in isolate populations enriched for CD9-binding parasites. Interestingly, IT4 parasite populations enriched for E-selectin- and CD151-binding parasites showed identical expression profiles to those of a parasite population exposed to wild-type CHO-745 cells. The same phenomenon was observed for the 3D7 isolate population enriched for binding to P-selectin, E-selectin, CD9 and CD151. This implies that the corresponding ligands for these receptors have either weak binding capacity or do not exist on the IE surface. Conclusively, this work expanded our understanding of P. falciparum adhesive interactions, through the identification of var transcripts that are enriched within the selected parasite populations.

characterizing the adhesive dynamics of Plasmodium falciparum infected erythrocytes (IEs) to different endothelial cell receptors (ECRs) in flow is a big challenge considering available methods. This study investigated the adhesive dynamics of IEs to five ECRs (CD36, ICAM-1, P-selectin, CD9, CSA) using simulations of in vivo-like flow and febrile conditions. To characterize the interactions between ECRs and knobby and knobless IEs of two laboratory-adapted P. falciplarum isolates, cytoadhesion analysis over time was performed using a new tracking bioinformatics method. The results revealed that IEs performed rolling adhesion exclusively over CD36, but exhibited stationary binding to the other four ECRs. The absence of knobs affected rolling adhesion both with respect to the distance travelled by IEs and their velocity. Knobs played a critical role at febrile temperatures by stabilizing the binding interaction. Our results clearly underline the complexity of the IE-receptor interaction and the importance of knobs for the survival of the parasite at fever temperatures, and lead us to propose a new hypothesis that could open up new strategies for the treatment of malaria. Cytoadhesion of Plasmodium falciparum to human endothelial cell receptors (ECRs) causes complications and deaths following malaria infection. In 2018, 405,000 malaria-related deaths were registered (61% of which were of children younger than 5 years old) 1. Cytoadhesion leads to accumulation of infected erythrocytes (IEs) within the microvascular bed of vital organs such as the brain, lungs, and kidneys. Death can eventually occur due to decreased blood supply and organ failure 2,3. Cytoadhesion results from interactions between members of the P. falciparum erythrocyte membrane protein 1 (PfEMP1) family and different ECRs 4-8. About 60 var genes per parasite genome encode PfEMP1 family members. Only one PfEMP1 variant is located on the membrane of IEs at the trophozoite stage, but the corresponding var gene is already expressed at the ring stage in a mutually exclusive pattern 9. The most studied interaction partners are the ECRs CD36, intracellular adhesion molecule 1 (ICAM-1), endothelial protein C receptor, and chondroitin sulfate A (CSA) 6,7. In general, PfEMP1 molecules cluster on nanoscale protrusions, called knobs, located on the membrane of IEs. Knobs consist of various submembranous structural proteins, predominantly knob-associated histidine-rich protein (KAHRP) 10. KAHRP contains several binding domains that interact with both parasite and host factors. Knobs begin to appear on the surface of IEs at 16 h post-invasion (hpi). The density of knobs increases from 20 to 60/µm 2 with parasite development from the

In vitro cultivation of Plasmodium falciparum is critical for studying the biology of this parasite. However, it is likely that different in vitro cultivation conditions influence various aspects of the parasite’s life cycle. In the present study two P. falciparum isolates were cultivated using the two most common methods, in which AlbuMAX or human serum as additives are used, and the results were compared. The type of cultivation influenced the knob structure of P. falciparum-infected erythrocytes (IEs). IEs cultivated with AlbuMAX had fewer knobs than those cultivated with human serum. Furthermore, knob size varied between isolates and is also depended on the culture medium. In addition, there was a greater reduction in the cytoadhesion of IEs to various endothelial receptors in the presence of AlbuMAX than in the presence of human serum. Surprisingly, cytoadhesion did not correlate with the presence or absence of knobs. Greater numbers of the variant surface antigen families RIFIN, STEVOR, and PfMC-2TM were found at the IE membrane when cultivated in the presence of AlbuMAX. Moreover, the type of cultivation had a marked influence on the transcriptome profile. Compared with cultivation with human serum, cultivation with AlbuMAX increased the expression of approximately 500–870 genes.

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