Leukocyte rolling in rat mesentery venules: Distribution of adhesion bonds and the effects of cytoactive agents

A new method of analyzing in vivo measurements of leukocyte WBC rolling along venular endothelium (EC) has been developed to extract insightful information on the dynamics of WBC-EC bond formation and disruption. The rolling velocity of WBCs was obtained by intravital microscopy of rat mesenteric venules. For the "spontaneous" rolling observed following exteriorization of the mesentery, we estimated that the average distance between clusters of adhesion bonds which tether a rolling cell to the venular wall was about 2 mum, and that the average lifetime of a bond cluster at the trailing edge of the rolling cell, from its exposure to the tensile force to its release, was on the order of 0.05 s. Both the inter-cluster distance and the lifetime were significantly reduced by treatments with the chemoattractant N-formyl-methionyl-leucyl-phenylalanine and the cytokine interleukin-l, while the average lifetime of the stretched bond clusters was not significantly changed by treatment with the cytoskeleton-modifying agents cytochalasin B and colchicine. Each of the four treatments significantly reduced the heterogeneity in the cell rolling velocity, presumably by the selective recruitment of WBC subsets from the circulating WBC population or by a reduction in the heterogeneity of endothelial adhesiveness. These results were analyzed in the context of in vitro data in the literature on molecular bonds of cell adhesion. The findings suggest that, in the case of "spontaneous" rolling, there are on average approximately 2-3 clusters of adhesion bonds between a rolling cell and the vessel wall, and approximately five bonds in each cluster. (C) 2001 Biomedical Engineering Society.