Maintaining vascular integrity and defending against invasive pathogens require the rapid regulation of adhesive interactions among blood cells and between blood cells and the vessel wall. Control of these mechanisms depends on the activation of adhesion receptors that are already present on resting blood cells and endothelium, or the expression of new receptors on the cell surface. Some functional overlap of adhesion receptors and their ligands adds a measure of safety to the repair and defense systems, but defective adhesion can occur and cause tissue injury or disrupt homeostasis of the vascular system.

The process that allows the extravasation of . . .