V-SNARE-DEPENDENT SECRETION IS REQUIRED FOR PHAGOCYTOSIS

Phagosomes are generally believed to form by gradual apposition of the plasma membrane of leukocytes onto the surface of invading microorgan isms. The internalization of the encapsulated particle is therefore pr edicted to reduce the surface area of the phagocyte, Contrary to this prediction, we observed that phagocytosis is associated with a net inc rease in cell surface area, suggesting the concomitant occurrence of e xocytosis. Selective cleavage of components of the secretory machinery by microinjection or transfection of bacterial neurotoxins induced a pronounced inhibition of phagocytosis. These observations indicate tha t vesicle-soluble N-ethylmaleimide-sensitive factor attachment protein receptor-mediated exocytosis of endomembranes is essential for optima l completion of particle internalization during phagocytosis.