The study by Marshall et al. investigates the mechanical behavior of bonds between adhesion molecules, specifically focusing on the interaction between P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1). Using atomic force microscopy (AFM) and flow-chamber experiments, the researchers demonstrate that these bonds exhibit both catch and slip behavior. Initially, increasing force prolongs bond lifetimes, indicating catch bonds, but after reaching a maximum, the lifetimes decrease, revealing slip bonds. This biphasic relationship suggests that the transition between catch and slip bonds might explain the biphasic pattern observed in leukocyte rolling on selectins, where the number of rolling cells first increases and then decreases with increasing wall shear stress. The findings provide a mechanism for regulating cell adhesion under variable mechanical stress and highlight the importance of catch bonds in maintaining stable adhesion at low shear stresses. The study also confirms that the catch-slip transition is specific to the P-selectin-PSGL-1 interaction, as other interactions, such as antigen-antibody interactions, do not exhibit this behavior.The study by Marshall et al. investigates the mechanical behavior of bonds between adhesion molecules, specifically focusing on the interaction between P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1). Using atomic force microscopy (AFM) and flow-chamber experiments, the researchers demonstrate that these bonds exhibit both catch and slip behavior. Initially, increasing force prolongs bond lifetimes, indicating catch bonds, but after reaching a maximum, the lifetimes decrease, revealing slip bonds. This biphasic relationship suggests that the transition between catch and slip bonds might explain the biphasic pattern observed in leukocyte rolling on selectins, where the number of rolling cells first increases and then decreases with increasing wall shear stress. The findings provide a mechanism for regulating cell adhesion under variable mechanical stress and highlight the importance of catch bonds in maintaining stable adhesion at low shear stresses. The study also confirms that the catch-slip transition is specific to the P-selectin-PSGL-1 interaction, as other interactions, such as antigen-antibody interactions, do not exhibit this behavior.