Malaria mRNA Transfer to Host Immune Cell

Malaria is the most serious mosquito-borne parasitic disease, caused mainly by the intracellular parasite Plasmodium falciparum (Pf). Upon their release from the liver, Pf parasites invade red blood cells (RBCs), in which they develop and replicate. It was discovered that while being entirely enclosed within the human RBCs, Pf parasites can deliver active cargo into immune cells via secreted extracellular vesicles (EVs) that shuttle different cargo, such as RNA, DNA and proteins between cells.

To understand the role of the RNA EV cargo in the course of malaria infection, we analyzed the RNA content for Pf-derived EVs. Importantly, we found that EVs contain parasitic small non-coding RNA molecules and full-length mRNA transcripts.

As a part of our efforts to elucidate the role of parasitic RNA cargo, we established a FISH assay, which enabled us to successfully detect a specific parasitic transcript (RESA mRNA) in the cytoplasm of recipient human monocytes upon internalization of the EVs. The results were validated by qPCR for RESA and other Pf mRNAs. Next, we investigated whether Pf-derived EV mRNA is translated inside host cells. For this, we established a polysome assay, in which we separate by a sucrose gradient the different populations of the ribosomes and search for parasitic mRNA. Further investigation of the translation profile of the recipient host cells showed no significant difference between cells that internalized EVs as compared to control cells.

These findings open new directions of investigation for understanding the molecular role of parasitic mRNA delivery into a human host.