Figure 5.

NETosis occurs in human abscesses due to Gram-positive bacterial infections. Five human patients presenting with Gram-positive abscesses were evaluated. Transmission electron microscopy was performed on freshly obtained clinical samples. (a) The abscesses contained intact neutrophils (PMN), red blood cells (RBCs), activated neutrophils with vesicles in the cytoplasm (PMNv), as well as numerous anuclear neutrophils with cytoplasmic granules and nuclear vesicles (arrowheads). (b) A typical anuclear neutrophil is demonstrated undergoing NET formation (arrowhead) and a second cell is shown, enlarged in (c), following nuclear envelope breakdown with dispersed chromatin and nuclear vesicles. The remnants of the nuclear envelope are highlighted (arrowhead). NETs are identified by the prototypical ‘beads on a string’ appearance on EM. (d) An anuclear neutrophil with nuclear envelope breakdown decondensed and dispersed chromatin (arrowhead), with vesicles and granules fusing with the outer plasma membrane (arrowhead). (e) Late stage neutrophils that have released chromatin and granules into the extracellular space.