Proteomic remodelling of human red blood cells and their extracellular vesicles across the intraerythrocytic cycle of Plasmodium falciparum
This study employs quantitative mass spectrometry to reveal that *Plasmodium falciparum* infection primarily remodels the protein composition of extracellular vesicles released by red blood cells—specifically by increasing complement components and parasite proteins—while causing only modest changes to the host cell's internal proteome, thereby supporting a model where infection-induced miRNAs function on recipient cells rather than within the infected red blood cell itself.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Malaria is a disease that hides inside the most basic building blocks of our blood. The parasite responsible, Plasmodium falciparum, invades red blood cells and turns them into factories for its own reproduction. For decades, scientists have known that the parasite does not just live inside these cells; it actively reshapes them, exporting hundreds of its own proteins to the surface to help it stick to blood vessel walls and avoid being filtered out by the spleen. We also know that red blood cells are not the silent, empty sacks they were once thought to be. They carry small genetic instructions called microRNAs, which can influence how other cells behave, and they release tiny bubbles called extracellular vesicles into the bloodstream. These bubbles act as messengers, carrying proteins and genetic material from the cell that made them to other cells in the body. The big question has been how the infection changes the actual proteins inside the red blood cell and in the bubbles it releases, and whether the genetic instructions found in the cell are actually being used to build new proteins.
A researcher set out to answer this by looking at the protein makeup of red blood cells at different stages of the malaria infection. They grew cultures of human red blood cells, infecting some with the malaria parasite while leaving others healthy. They waited for the parasites to reach two specific stages of their life cycle: the ring stage, which is early in the infection, and the trophozoite stage, which is more mature. From these cultures, they collected the red blood cells themselves and also purified the tiny bubbles, or vesicles, that the cells had released into the surrounding fluid. Using a powerful technique that weighs and identifies thousands of proteins at once, they mapped out exactly which proteins were present in the healthy cells, the infected cells, and the bubbles from both groups. They did this three times for each group to ensure the results were reliable.
The first thing the researcher found was that the parasite's own presence was easy to track. In the healthy cells, they found almost no parasite proteins. As the infection progressed to the ring stage, a small number of parasite proteins appeared. By the time the parasite reached the mature trophozoite stage, the number of parasite proteins had grown significantly, making up a larger share of the total protein in the cell. This confirmed that the parasite was successfully building its own machinery inside the host. The researcher also identified seven specific parasite proteins that are known to remodel the host cell, and they found that these proteins were not just staying inside the cell but were also being released into the tiny bubbles outside. This suggests that the parasite is actively sending its tools out into the bloodstream.
What was perhaps more surprising was how little the human part of the cell changed. Red blood cells do not have a nucleus, which means they cannot make new genetic instructions or easily build new proteins in response to a threat. The researcher expected that the infection might trigger a massive change in the human proteins inside the cell, but they found the opposite. The list of human proteins remained largely the same, with no single human protein showing a statistically significant change in amount. The cell did not mount a protein-based defense. Instead, the changes were subtle and focused on the cell's internal structure, with a slight increase in the proteins that form the cell's skeleton and a decrease in the hemoglobin that carries oxygen. This lack of a dramatic protein response makes sense for a cell that has lost its ability to read new genetic instructions.
The story changed completely when the researcher looked at the tiny bubbles, or vesicles, that the cells released. While the cells themselves remained mostly unchanged, the bubbles they sent out were very different. In the bubbles from infected cells, the researcher found a massive and coordinated increase in proteins belonging to the complement system. The complement system is a group of proteins in our blood that helps the immune system fight infection by tagging invaders and triggering inflammation. In the bubbles from infected cells, twenty-three different components of this system rose together, while proteins that usually calm the immune response did not increase. At the same time, proteins that act as the body's antibodies dropped in the bubbles. This means that the infected red blood cell is not just changing its own interior; it is actively altering the message it sends to the rest of the body, loading its messenger bubbles with immune-activating proteins.
The researcher also checked whether the genetic instructions, or microRNAs, that they had previously found in these cells were actually working to change the proteins inside. They had identified several microRNAs that were predicted to target genes involved in the immune response. However, when they looked for the proteins that those genes would produce, they found none of them. The immune proteins simply were not there. This confirms that the microRNAs are not acting inside the red blood cell to change its own behavior. Instead, the evidence points to a different role: these microRNAs are likely packaged into the bubbles and sent out to act on other cells in the body. The red blood cell, unable to change its own protein makeup, is instead changing the composition of the messages it sends out.
The study concludes that the main effect of the malaria infection on the red blood cell is not a change in what the cell is made of, but a change in what it releases. The cell accumulates the parasite's own proteins and remodels its internal skeleton, but its most significant action is to release bubbles filled with immune-stimulating proteins. This finding helps explain how a single infected cell can influence the entire body, potentially contributing to the severe inflammation seen in serious cases of malaria. The research suggests that the infected red blood cell acts less like a victim trying to defend itself and more like a broadcaster, sending out signals that alter the behavior of the immune system and other cells in the circulation.
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