Endothelial cells (EC) play multiple, pivotal roles in the pathogenesis of inflammation throughout the body. Endothelium is a major element in homeostasis, while in disease its impairment, notably by cytokines, causes phenotypic and functional modifications, for example pro-coagulation and -adhesion, increased permeability, apoptosis and changes in functional properties, which directly correlate with mortality in severe syndromes such as cerebral malaria (CM) or sepsis.
Extracellular vesicles (EV) are essential mediators of intercellular communication between the pathogen, the immune system and EC of the blood-brain barrier.
In this study, we modelled CM in vitro by co-culturing human brain microvascular endothelial cells and P. falciparum-IE (infected erythrocytes), then characterised EV released into the supernate. We compared two P. falciparum strains that differed by their binding specificity to brain endothelium: 3D7, which binds to CD36, and E8B, which binds to ICAM-1. Both parasites induced a dramatic increase in numbers of annexin V+ microvesicles (MV), when compared to what was released with non-infected erythrocytes, as disclosed by flow cytometry. Double labelling indicated that E8B parasites induced significantly more CD105+ MV than did 3D7. We further characterised the vesicles by nanoparticle tracking analysis (NTA), which confirmed that EC-IE supernates had more vesicles than other groups and was the only test condition with vesicles around 500 nm. Interestingly, NTA revealed that the majority of EV released upon contact between IE and brain EC were in the 100-200 nm range, suggesting that exosomes may be a major class.