Theoretical modeling of actin-retrograde-flow passing clusters of confined T cell receptors

Through the activation process of T cells, actin filaments move from the cell periphery toward the cell center. The moving filaments engage with T cell receptors and thus contribute to transportation of the signaling molecules. To study the connection between the moving actin filaments and T cell receptors, an experiment available in the literature has measured filaments flow velocity passing over a region of confined clusters of receptors. It shows that flow velocity decreases in the proximity of the receptors, and then regains its normal value after traversing the region, suggesting a dissipative friction-like connection. In this work, we develop a minimal theoretical model to re-examine this experiment. The model brings the insight that, in contrast to the first impression that the experiment gives, the direct necessity of having a minimum in the velocity profile is not the locally high friction region, but a combined driving force of push from upstream and pull from within and downstream of the system. The predicted driving force integrates our current understanding of the spatially dependent role of the myosin motor proteins and the actin-polymerization-machinery, which make the pulling and pushing forces, respectively.