Regulation of Adhesion Receptors Expression in Endothelial Cells
The endothelium consists of a single layer of tightly connected cells forming a boundary between the vascular lumen and the underlying tissues. Endothelial cells (EC) are polarized, having a luminal membrane in contact with the blood and an abluminal membrane adherent to the subendothelial matrix. These two membranes are functionally and chemically distinct. The luminal membrane, in fact, is nonadhesive and allows the free flow of blood cells; the abluminal membrane is firmly adherent to the basal lamina providing anchorage to the subendothelium. The endothelium is a dynamic tissue which controls the traffic of cells and metabolites across the vessel wall in physiological conditions and is involved in the regulation of hemo- stasis and inflammatory and immune responses. During these processes specific stimuli induce EC activation. This process involves a series of morphological and functional changes, including regulation of adhesion receptors and reorganization of theactin cytoskeleton and of the extracellular matrix (for review see Cotran and Pober 1988). Activation also leads to the production of different mediators such as prostaglandin l2, platelet-activating factor (PAF), interleukin-8 and monocyte/chemoattractants protein-1 (for review see Mantovani etal. 1992). Upon activation the luminal membrane of EC exposes specific receptors allowing the binding of leukocytes and their subsequent migration into tissues. We recently showed that the abluminal membrane also undergoes specific changes in adhesion receptors leading to altered cell-matrix interactions.
KeywordsAdhesion Receptor Luminal Membrane Postcapillary Venule Integrin Complex Lymphocyte Binding
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