Tracking Rotation during Leukocyte Rolling Reveals Asymmetric Adhesion Properties

Leukocytes are responsible for fighting infections in the body. When injuries occur, selectin molecules are expressed on the surface of nearby blood vessel walls. These selectin molecules transiently adhere to leukocytes flowing in the bloodstream and capture them, leading to leukocyte rolling towards the injury site. Rolling adhesion is critical for leukocytes to locate injury sites and to activate various signaling pathways for subsequent transmigration and chemotaxis.Individual adhesion components involved in rolling adhesion, such as adhesion molecules and membrane tethers have been characterized. However, models incorporating these properties are still unable to describe fully the rolling behavior. Current models assume uniformly distributed adhesion properties on cell surfaces due to the lack of measurements quantifying this distribution. Here, we determined experimentally the spatial distribution of adhesive properties on leukocyte surfaces. We used dark-field imaging and particle tracking techniques to extract not only the translational but also the rotational motion of a single rolling cell. The additional rotational information allows us to map precisely the whole cell motion and adhesion properties to a particular cell orientation. We find that the adhesion properties of the leukocyte surface are far from homogenous, with large, localized patches on the cell surface exhibiting strong or weak adhesive properties. This finding provides new insight into leukocyte adhesion properties, such as the asymmetric distribution of receptor and microvilli on rolling cells, and could lead to better modeling of rolling adhesion.