FIG. 1.

The multistep model of PMN capture, rolling, firm adhesion, and transendothelial migration. (A) The resting PMN express selectin ligands, but selectins are not present on the resting endothelium. Hence, PMN do not interact with the endothelium in resting stage. (B) Stimulation of the endothelium by proinflammatory mediators triggers the expression of selectins. The tethering on selectins and selectin ligands facilitates primary PMN capture to the endothelium and secondary PMN–PMN recruitment. Tethering transitions to rolling and results in activation of β2-integrins. (C) The interaction of β2-integrins with ICAM-1 upregulated on the activated endothelium causes the arrest, followed by spreading and then crawling, and finally trans endothelial migration of PMN. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article at www.liebertonline.com/ars).