Plasma membrane vesiculation: correlation between macrophage spreading and the shedding of cell surface vesicles.

The data presented in this paper establish a correlation between the extent of macrophage spreading and the ability of macrophages to shed plasma membrane vesicles following incubation in a membrane vesiculant. Maximal macrophage spreading was observed following incubation in buffers containing Mn2+ or dithiothreitol. Scanning electron microscopy showed that such macrophages have a uniformly flat surface morphology. Exposure of these macrophage monolayers to a vesiculant containing 25 mM formaldehyde-2 mM dithiothreitol induced plasma membrane vesiculation. Scanning electron microscopy further demonstrated that vesicles were formed and released randomly over the cell surface and that vesicles varied in size from 1 to 15 micrometer. diameter. A variety of chemicals that share the common ability to bind to free sulfhydryl groups have been shown to act as membrane vesiculants as a result of their apparent ability to induce a unique form of cell injury which results in the shedding of cell surface vesicles. The differential effect of vesiculants on cells grown in suspension and as monolayer is interpreted to suggest that reorganization of the cellular cytoskeleton associated with cell spreading may underlie the ability of membrane vesiculants to induce plasma membrane vesiculation in highly spread and adherent macrophage monolayers.