Leukocyte emigration can be subdivided into a series of steps or stages: tethering/rolling (transient adhesive interactions) arrest. Firm or stable adhesion (leukocyte flattening or spreading) Intravascular crawling transendothelial migration or diapedesis (migration between or through endothelial cells) Inflammatory il-1/tnfa activate endothelial cells to express adhesion molecules: Contain a calcium-dependent lectin domain with an adjacent egf-like domain. The lectin domain binds a small carbohydrate molecule called sialylated lewis x or slex slex is expressed on glycoproteins like mucins, where serine/threonine are glycosylated (o- linked). Psgl-1 is the main leukocyte ligand of endothelial cell selectins. Optimal p-selectin binding requires tyrosine sulfation of psgl-1 near its amino terminus. Immunoglobulins (ig): icam-1, icam-2, vcam-1 and pecam-1 ligands. Type 1 transmembrane glycoproteins containing ig homology domains. Icam-1, vcam-1 binds leukocyte integrins and mediates arrest, adhesion and intravascular crawling. Integrins provide a link between the cell cytoskeleton and the extracellular matrix. Integrins are clustered in focal adhesion complexes as signaling molecules.