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 microorganisms. The internalization of the encapsulated particle is therefore predicted to reduce the surface area of the phagocyte. Contrary to this prediction, we observed that phagocytosis is associated with a net increase in cell surface area, suggesting the concomitant occurrence of exocytosis. Selective cleavage of components of the secretory machinery by microinjection or transfection of bacterial neurotoxins induced a pronounced inhibition of phagocytosis. These observations indicate that vesicle-soluble N-ethylmaleimide-sensitive factor attachment protein receptor-mediated exocytosis of endomembranes is essential for optimal completion of particle internalization during phagocytosis.