Rotation Tracking and Adhesion Footprinting Reveal Asymmetric Rolling Adhesion Mechanism

Abstract

Rolling adhesion is the behaviour that leukocytes and circulating tumour cells exhibit as they passively roll along blood vessel walls under flow. It plays a critical role in capturing cells in the blood, guiding them toward inflammation sites, and activating cell signalling pathways to enable their subsequent transmigration. Rolling adhesion is mediated by catch-bond-like interactions between selectins expressed on endothelial cells lining blood vessels and P-selectin glycoprotein ligand-1 (PSGL-1) found at microvilli tips of leukocytes. Despite our understanding of individual components of this process, how the molecular details of adhesion bonds scale to cell-surface adhesion and rolling behaviour remains poorly understood. Here, we developed a method that maps the functional adhesion sites and their strength on a leukocyte surface. The method relies on tracking the rotational angle of a single rolling cell, which confers advantages over standard methods that track the centre-of-mass alone. Constructing the adhesion map from the instantaneous angular velocity reveals that the adhesion profile along the rolling circumference is inhomogeneous. We corroborated these findings by obtaining a footprint of molecular adhesion events using DNA-based molecular force probes. Our results reveal that adhesion at the functional level is not uniformly distributed over the leukocyte surface as previously assumed, but is instead patchy.