Fig. 1. Leukocyte–endothelial cell adherence and transmigration after ischemia–reperfusion. Activated leukocytes interact with the vascular endothelium via  a series of distinct steps. The initial “rolling” step is initiated by ischemia–reperfusion–induced increases in endothelial P-selectin expression, which interacts with its leukocyte counterreceptor, P-selectin glycoprotein 1 (PGSL-1) (1). Interaction of leukocyte β²integrins, CD11a/CD18 and CD11b/CD18, with endothelial intercellular adhesion molecule 1 (ICAM-1) results in firm leukocyte adherence and aggregation (2). Leukocyte transmigration into the interstitial compartment is facilitated by platelet-endothelial cell adhesion molecule 1 (PECAM-1) within the endothelial cell junctions (3).