Fig. 2. Force versus time traces for E-selectin binding to PMNs in the absence (A) and presence (B) of EDTA. Experimental conditions, including selectin concentration on the cantilever, contact force and dwell time, were optimized for both E-selectin and L-selectin experiments to result in 30% binding events (30 adhesion events per 100 contacts). The arrows indicate rupture events with magnitudes of about 100 pN taken from an experiment with a reproach velocity of 15 µm second^–1. The presence of EDTA was consistently found to eliminate receptor-ligand binding. The linear increase in slope just before each rupture event is indicative of the loading rate exerted on the receptor-ligand bond (Benoit et al., 2000; Li et al., 2003; Wojcikiewicz et al., 2003).