Formation of a protein corona on the surface of extracellular vesicles in blood plasma

In this study we tested whether a protein corona is formed around extracellular vesicles (EVs) in biofluids. We isolated nascent EVs of THP1 cells and platelets, and incubated them in EV-depleted platelet-free plasma from healthy subjects and patients with rheumatoid arthritis. EVs were subjected to differential centrifugation, size exclusion chromatography, or density gradient ultracentrifugation followed by mass spectrometry. Plasma protein-coated EVs had a higher density compared to nascent ones and carried numerous newly associated proteins. Interactions between plasma proteins and EVs were confirmed by immune electron microscopy and flow cytometry. Based on the results of this study and data published by others, we identified 9 shared corona proteins (ApoA1, ApoB, ApoC3, ApoE, CO3, CO4B, FIBA, IgHG2 and IgHG4) equally present in association with EVs, viruses and artificial nanoparticles in blood plasma. Since ALBU was also present in association with our nascent EVs, we could not include it in the list. We found induction of protein aggregation by centrifugation of our EV-depleted plasma samples at 12,500 g and the aggregate proteins showed high overlap with the EV corona. However, in contrast to aggregates which had no effect, coated EVs induced an increased expression of TNFa, IL-6 and CD83 of human monocyte-derived dendritic cells. In conclusion, our data shed new light on the commonly reported plasma protein “contamination” of EV preparations.