Fig 8. Direct comparison of experimental data with the predictions of the protrusive zipper model with discrete adhesion.

(A) Time courses of the cell-substrate contact area predicted by the protrusive zipper model with discrete adhesion are overlaid on experimental results for two different ligand densities. The model curves are not the result of nonlinear fits but simply the predictions based on reasonable choices of parameter values. (B) The predicted ligand-density-dependent increase in maximum contact area agrees well with experimental results obtained in frustrated phagocytosis experiments. Modeling only ligands as discrete entities results in an apparent overestimation of the maximum contact area at the highest IgG density (solid blue curve), indicating that the number of Fcγ receptors rather than the number of IgG ligands becomes the limiting factor of the maximum adhesion strength in this regime. A model version that accounts for the discrete nature of both ligands as well as receptors (Appendix F in S1 Appendices) improves the agreement with the data at the highest IgG density (dashed red curve). Error bars indicate standard deviation.