Figure 1.

Adhesion probability of human neutrophils to VCAM-1 coated bead as a function of time. (A) Solid curve is based on a nonlinear least-squares regression of first-order kinetic theory (Eq. 1) to expected bond number 〈n〉 obtained from measurements of adhesion probability as a function of contact time for beads with a surface density of VCAM-1 (ρ₁) of 310 sites/μm². Data for these beads are shown as solid triangles. The dashed curve shows the theoretical prediction based on Eq. 1 and the kinetic parameters obtained for the solid curve but with ρ₁ set to 860 sites/μm². Measured values for adhesion to the 860 sites/μm² beads are shown as the open circles. The discrepancy between measurement and simple first-order theory is evident. Bars represent standard error of the mean. Between 20 and 40 cell-bead pairs were tested for each data point. Probability values have been corrected for nonspecific adhesion (Eq. 14) and adjusted to account for differences in contact area. (See companion report for details (18).) (B) Predictions based on the assumption that the measured adhesion probability is the product of a constant probability that an RZ exists (P_RZ = 0.35) and a first-order P_〈n〉, consistent with Eq. 1. The solid curve corresponds to the fit to data obtained using beads with VCAM density of 860 sites/μm² (solid triangles), and the dashed curve is generated from the fitted parameters but with a lower VCAM density (310 sites/μm²). Discrepancies between the predictions and measurements for the lower density beads (open circles) are evident. Probability values have been corrected for nonspecific adhesion before the calculations.