Transit time of leukocytes rolling through venules controls cytokine- induced inflammatory cell recruitment in vivo

Leukocyte recruitment requires leukocyte rolling, activation, firm adhesion, and transmigration. Injection of the proinflammatory cytokine TNF- α induces expression of E-selectin, interleukin-8, and other adhesion molecules and chemoattractants on the endothelial surface. TNF-α-treated CD18 null mouse cremaster muscle venules show increased leukocyte rolling velocity and reduced leukocyte recruitment efficiency. Leukocyte recruitment in CD18 null but not wild-type mice is significantly blocked by an mAb to E- selectin. To understand this overlap between adhesion events previously considered separate, we introduce a quantitative analysis of the efficiency of induction of rolling, conversion of rolling to adhesion, and of adhesion to transmigration. We find that CD18 and E-selectin cooperate to control the time a leukocyte needs to roll through an inflamed area and to convert rolling to firm adhesion. Leukocyte rolling time, defined as the time it takes for a rolling leukocyte to pass through a defined length of a vessel segment, emerges as a unifying parameter determining the efficiency of inducing firm adhesion, which is a rate-limiting step controlling leukocyte recruitment in inflammation. We conclude that leukocytes integrate chemoattractant signals while rolling along the endothelial surface until they reach a critical level of activation and become firmly adherent.