Functionally and morphologically distinct populations of extracellular vesicles produced by human neutrophilic granulocytes.

Abstract

EVs in the microvesicle size range released during spontaneous death of human neutrophils were characterized and their properties compared with previously described EVs with antibacterial effect (aEVs, generated on specific activation) or produced spontaneously (sEVs). The 3 vesicle populations overlapped in size and in part of the constituent proteins were stained with annexin V and were impermeable to PI. However, none of them produced superoxide. In contrast, remarkable differences were observed in the morphology, abundance of proteins, and antibacterial function. EVs formed spontaneously in 30 min (sEVs) were more similar to EVs released during spontaneous death in 1-3 days than to EVs formed in 30 min on stimulation of opsonin receptors (aEVs). Spontaneously generated EVs had no antibacterial effect despite their large number and protein content. We hypothesized 2 parallel mechanisms: one that proceeds spontaneously and produces EVs without antibacterial effect and another process that is triggered by opsonin receptors and results in differential sorting of proteins into EVs with antibacterial capacity. Our results call attention to the functional and morphologic heterogeneity within the microvesicle/ectosome fraction of EVs.