Receptor mobility, the cytoskeleton, and particle binding during phagocytosis.

Particle engulfment during phagocytosis has long been appreciated to be an active, actin-driven process. By contrast, the preceding stage--securing the target to the surface of the phagocyte--was thought to result from the passive diffusion of receptors along the membrane towards their ligands on the particle surface. Recent evidence, however, challenges this notion, demonstrating that receptors do not diffuse freely along the phagocyte surface and that actin polymerization and tyrosine phosphorylation are required for optimal particle binding. The interpretation and significance of these observations are the subject of this opinion piece.