Extracellular vesicles from early-stage P. falciparum-infected red blood cells contain PfEMP1 and induce transcriptional changes in human monocytes.

Pathogens can release extracellular vesicles (EVs) for cell-cell communication and host modulation. EVs from Plasmodium falciparum, the deadliest malaria parasite species, can transfer drug resistance genes between parasites. EVs from late-stage parasite-infected RBC (iRBC-EVs) are immunostimulatory and affect endothelial cell permeability, but little is known about EVs from early-stage iRBC. We detected the parasite virulence factor PfEMP1, which is responsible for iRBC adherence and a major contributor to disease severity, in EVs only up to 12 hours-post RBC invasion. Furthermore, using PfEMP1 transport knock-out parasites, we determined that EVs originated from inside the iRBC rather than the iRBC surface. Proteomic analysis detected 101 parasite and 178 human proteins in iRBC-EVs. Primary human monocytes stimulated with iRBC-EVs released low levels of inflammatory cytokines, and showed transcriptomic changes. Stimulation with iRBC-EVs from PfEMP1 knock-out parasites induced more gene expression changes, and affected pathways involved in defense response, stress response, and response to cytokines, suggesting a novel function of PfEMP1 when present in EVs. We show for the first time the presence of PfEMP1 in early-stage P. falciparum iRBC-EVs, and the effects of these EVs on primary human monocytes, uncovering a new mechanism of potential parasite pathogenesis and host interaction.