Selectins neutrophil-endothelium interactions

On the neutrophil, the major selectin expressed is L-selectin. This molecule is constitutively expressed on mature neutrophils but may be expressed at low levels (50% of adult) in neonates. Stimulation of endothelial cells with thrombin, histamine, IL-1 and some other agents induces neutrophils (and other leukocytes) to leave the circulation and adhere to the endothelium. They do this by rolling onto the surface of the endothelium, to which they attach via P-selectin translocated from storage sites in Weibel-Palade bodies to the surface of the endothelium upon activation. The expression of P-selectin is short-lived and is replaced on the endothelial surface by E-selectin (whose expression is also regulated by some cytokines), which continues the endothelial-leukocyte interaction. 

Thirdly, there are the selectins, a family of Ca Mependent carbohydrate-binding proteins which function to control leukocyte interactions with vascular endothelium (Tedder et al, 1995). There are three closely related members of the selectin family, namely L (leukocyte)-, P (platelet)-, and E (endothelial)-selectin. P-selectin is expressed in the Weibel-Palade bodies of endothelial cells and in the a-granules of platelets. It is rapidly mobilized to the sur ce of endothelial cells and platelets in response to a variety of inflammatory agents such as fiuombin, histamine, complement factors, fiee radicals and cytokines (Tedder et al, 1995). P-selectin mediates the adhesion of neutrophils and monocytes to activated platelets and endothelial cells. Platelets can be bound to the endothelium indirectly by adhering to leukocytes bound to the endothelium. 

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