Figure 4.

Types of phagocytosis and the model variables. (A) In CR3-mediated phagocytosis, the particle sinks into the cell, in a manner similar to endocytosis. (B) In contrast, in Fcγ-mediated phagocytosis, the membrane extends via pseudopod extensions outwards around the particle. Despite these differences, we believe that the movement of receptors within the membrane is similar in both cases, and can be described by the same simple model. (C) Sketch of the receptor density, ρ, which depends only on the distance from the center of the cup, r, and the time, t. Within the cup, which has arc length a, the receptor density is always fixed at ρ_L, whereas the density at infinity, which is the same as the initial density, is ρ₀. At the edge of the cup, the receptor density is fixed at ρ₊, which is calculated by considering the free energy. In the pure diffusion model, ρ₊ is always less than ρ₀, so that receptors always flow in toward the cup and increase the cup size. To see this figure in color, go online.