Effects of shear stress and different conditions of activation on rolling velocities. Plots of mean rolling velocities of >25 PMN (mean ± SEM; n = 4). Circles indicate maximally activated HUVEC++ (LPS 100 ng/ml) with non-activated or activated PMN (PMN- and PMN++ respectively). Triangles indicate sub-maximally activated HUVEC+ (LPS 10 ng/ml) with non-activated or activated PMN (PMN- and PMN+ respectively). Square symbols indicate non-activated controls (HUVEC-/PMN-). In non-activated and sub-maximal activated cultures without E-selectin expression, rolling PMN were too few to calculate mean velocities above 1 dyne/cm2. Maximal activation of HUVEC prevailed constant rolling velocities between 3 and 1 dyne/cm2 characteristic for selectin-interactions. Reduction of shear stress below a critical threshold increased rolling velocities followed by a decrease with further reduction of shear stress along with the reduction in hydrodynamic flow velocity. In cultures without E-selectin markedly increased rolling velocities were observed already at 1 dyne/cm2.