Ectosomes Released by Human Neutrophils Are Specialized Functional Units

Abstract

Here we show that human polymorphonuclear leukocytes (PMN) release ectosomes independently of complement attack during their activation both in vitro and at the site of inflammation in vivo. Patterns of biotinylated proteins on the surface of PMN and on PMN-derived ectosomes indicated a specific sorting of cell surface proteins into and out of ectosomes. Ectosomes expressed clusters of complement receptor 1 (CR1), which allowed them to bind efficiently to opsonized bacteria. Myeloperoxidase and human leukocyte elastase, both stored within the azurophilic granules of PMN, were found to colocalize on ectosomes with CR1. Furthermore, myeloperoxidase colocalized with human leukocyte elastase. In contrast, not present on CR1-expressing ectosomes were CD63, a selective marker for the azurophilic granules, and CD14, which is located within the same granules and the secretory vesicles as CR1. Of the other complement regulatory proteins expressed by PMN, only CD59 colocalized with CR1, while CD55 and CD46 were almost absent. Ectosomes released by activated PMN at the site of inflammation may function as a well organized element (ecto-organelle), designed to focus antimicrobial activity onto opsonized surfaces.

Activation-induced mobilization of secretory vesicles in bovine neutrophils

“…For example, IL-8 and PAF induced a dose-dependent increase in cell-surface alkaline phosphatase activity over a wide range of effector concentrations, whereas PMA induced a biphasic response with up-regulation of cell-surface alkaline phosphatase activity at low doses (1 ng/ml) and a return to baseline values or, in some cases, even a reduction in cell-surface alkaline phosphatase activity at higher doses. The reason for the decrease in cell-surface alkaline phosphatase activity on cells treated with ≥ 10 ng of PMA/ml is not clear; however, in another study, 36 it was documented that neutrophils treated with PMA, fMLF, or ionomycin released cell-surface vesicles (ectosomes) in a dosedependent manner. Thus, higher doses of PMA may be stimulating release of ectosomes, resulting in loss of cell-surface alkaline phosphatase, compared with the amount that remains inside the cell.…”

Clathrin mediates both internalization and vesicular release of triggered T cell receptor at the immunological synapse

“…Formation of large vesicles at the plasma membrane can take place through a process of blebbing ( 51 ). Given the precedent of referring to small vesicles that bud from the plasma membrane as ectosomes ( 52 ), we suggest clathrin- and ESCRT-mediated ectocytosis (CEME) as a term to describe this process.…”

Lipidome profiling of human and equine neutrophil-derived extracellular vesicles and their potential contribution to the ensemble of synovial fluid-derived extracellular vesicles during joint inflammation

“…The lipidomic composition of nEVs from activated neutrophils has been indicative of the presence of ectosomes (e.g., microvesicles or apoptotic bodies) Hess et al [1999]. Additionally, the diverse sizes and shapes observed in nEVs suggest potential heterogeneity in biogenesis routes.…”