Electron micrographs of the vesicle preparations from filtrates. Filtrates from experiments studying in vitro AaPAL release into serum were subjected to vesicle preparation and subsequent electron microscopy. The filtrates were: A. actinomycetemcomitans D7SS at 8 h (Panel A), D7SS-p at 8 h (Panel B), No bacteria control at 2 h (Panel C). The vesicle preparation from A. actinomycetemcomitans D7SS whole cells (positive control) shows vesicles of different sizes indicated by arrows (Panel D). Bars; 0.2 μm.