Direct ex vivo gene expression profiling of malaria patients reveals common virulence gene expression in first-time infected patients and severe cases

Sequestration of Plasmodium falciparum-infected erythrocytes to host endothelium through the parasite-derived PfEMP1 adhesion proteins is central to the development of malaria path-ogenesis. PfEMP1 proteins have diversified and expanded to encompass many sequence variants conferring the same array of human endothelial receptor binding phenotypes. Here, we analyzed RNA-seq profiles of parasites isolated from 32 P. falciparum infected travelers returning to Germany. Patients were categorized into either malaria naive (n=15) or pre-exposed (n=17), and into severe (n=8) or non-severe (n=24) cases. Expression analysis of PfEMP1-encoding var genes showed that severe malaria was associated with PfEMP1 con-taining the endothelial protein C receptor (EPCR)-binding CIDRα1 domain, whereas CD36-binding PfEMP1 was linked to non-severe malaria outcomes. In addition, gene expression-guided determination of parasite age suggested that circulating parasites from non-severe malaria patients were older than parasites from severe malaria patients. First-time infected patients were also more likely to develop severe symptoms and tended to be infected for a longer period, which thus appeared to select for parasites with more efficient sequestration and therefore more pathogenic PfEMP1 variants.