Theoretical model of efficient phagocytosis driven by curved membrane proteins and active cytoskeleton forces

Phagocytosis is the process of engulfment or internalization of comparatively larger particles by the cell, that plays a central role in our immune system. We study the process of phagocytosis by considering a simplified coarse grained model of a three-dimensional vesicle, having uniform adhesion interaction with a particle, in the presence of curved membrane proteins and active cytoskeleton forces. We note that the complete engulfment is achieved when the bending energy cost of the vesicle is balanced by the gain in the adhesion energy. The addition of curved proteins reduces the bending energy cost at the highly curved leading edge, and thereby the engulfment is achieved at smaller adhesion strength. The curved proteins form the rim of the phagocytic cup that wraps around the particle and makes the engulfment process more efficient than in a protein-free vesicle. The presence of active force allows the formation of the phagocytic cup at even smaller protein density, and the engulfment is achieved more quickly. We consider spherical as well as non-spherical particles (spheroid, sphero-cylinder etc.) and note that the non-spherical particles are more difficult to engulf in comparison to the spherical particles of the same surface area. For non-spherical particles, the engulfment time crucially depends upon the initial orientation of particles with respect to the vesicle. Our results are in agreement with the experiments performed either using artificial particles or the bacterial engulfment by the immune cell.