Figure 4.

Proposed model of the cellular forces involved during internalization by phagocytosis. Phagosome formation is driven by a protrusive force (red arrows), generated by the polymerization of actin filaments, directed along the particle by an attractive force (purple arrows), and coupling proteins that anchor the actin cytoskeleton to the cell-particle interface. The protrusive force works against the surface tension, composed of the cortical tension (pink arrows) and the membrane tension (blue arrows). The rate of deformation of the cell is determined by the ratio of the surface tension and the cytoplasm viscosity, while the surface tension effectively propels the particle inward. The in-line tension of the plasma membrane is compensated by the flattening of surface folds of the membrane and the exocytosis of intracellular vesicles.