Objective: Leukocyte extravasation is critical in the immune response. Leukocytes transmigrate from apical to basal endothelium preferentially through VEC junctions three-dimensionally (3D), a process known as diapedesis. However, the precise biomechanical mechanisms by which the leukocyte-VEC interaction contributes to diapedesis remain elusive.
Method: We conducted time-lapse imaging experiments to monitor the dynamics of VEC junctions during leukocyte diapedesis. We used 3D Traction Force Microscopy (3DTFM) and Monolayer Stress Microscopy to measure the spatiotemporal evolution of the traction stresses and intracellular tensions generated by the cells and to characterize the sequence of mechanical events during leukocyte diapedesis. We acquired 4-6 experiments for the statistical analysis.
Results: We found that leukocyte firm adhesion caused the opening of junctional gaps before the initiation of leukocyte transmigration. We measured significant changes of in-plane stress and intracellular tension while the leukocyte firmly attached to VECs, and subsequently, the following increases of out-of-plane stress as the leukocyte migrates across the monolayer. Thrombin treatment increased the heterogeneity of VEC monolayer tensions, which created a VEC environment that facilitated leukocyte diapedesis. Subsequent treatment with Rho kinase inhibitor reversed the thrombin effect.
Conclusion: The coordination between 3D traction stresses and VEC monolayer tensions, controls the dynamics of leukocyte diapedesis.