Enhanced permeability and retention (EPR) effect

Vascular permeability, often in the form of capillary permeability or microvascular permeability, characterizes the capacity of a blood vessel wall to allow for the flow of small molecules (drugs, nutrients, water, ions) or even whole cells (

lymphocyte A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic a ...

s on their way to the site of

inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molec ...

) in and out of the vessel.

Blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide awa ...

walls are lined by a single layer of

endothelial The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the ve ...

cells. The gaps between endothelial cells (

cell junction Cell junctions (or intercellular bridges) are a class of cellular structures consisting of multiprotein complexes that provide contact or adhesion between neighboring cells or between a cell and the extracellular matrix in animals. They also main ...

s) are strictly regulated depending on the type and physiological state of the tissue. There are several techniques to measure vascular permeability to certain molecules. For instance, the cannulation of a single microvessel with a micropipette, the microvessel is perfused with a certain pressure, occluded downstream and then the velocity of some cells will be related to the permeability.Michel, C. C., Mason, J. C., Curry, F. E. & Tooke, J. E. Development of Landis Technique for Measuring Filtration Coefficient of Individual Capillaries in Frog Mesentery. Q J Exp Physiol Cms 59, 283-309 (1974).Bates, D. O. & Harper, S. J. Regulation of vascular permeability by vascular endothelial growth factors. Vascul Pharmacol 39, 225-237 (2002) Another technique uses multiphoton fluorescence intravital microscopy through which the flow is related to fluorescence intensity and the permeability is estimated from the Patlak transformation Patlak, C. S., Blasberg, R. G. & Fenstermacher, J. D. Graphical evaluation of blood-to-brain transfer constants from multiple-time uptake data. J Cereb Blood Flow Metab 3, 1-7 (1983). of the intensity data Reyes-Aldasoro, C. C. et al. Estimation of apparent tumor vascular permeability from multiphoton fluorescence microscopic images of P22 rat sarcomas in vivo. Microcirculation 15, 65-79 (2008). In cancer research, the study of permeability of the microvasculature that surrounds tumours is of great interest as the vascular wall is a barrier of large molecules into the tumours, the vessels control the microenvironment which affect tumour progression and changes to the permeability may indicate vascular damage with drugs.Tozer GM, Kanthou C, Baguley BC. (2005). Disrupting tumour blood vessels. Nat Rev Cancer 5:423– 435 An example of increased vascular permeability is in the initial lesion of periodontal disease, in which the gingival plexus becomes engorged and dilated, allowing large numbers of

neutrophil Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying ...

s to

extravasate __NOTOC__ Extravasation is the leakage of a fluid out of its container into the surrounding area, especially blood or blood cells from vessels. In the case of inflammation, it refers to the movement of white blood cells from the capillaries to th ...

and appear within the junctional epithelium and underlying

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

.Page, RC; Schroeder, HE. "Pathogenesis of Inflammatory Periodontal Disease: A Summary of Current Work." ''Lab Invest'' 1976;34(3):235-249

References

External links

* {{MeshName, Vascular+Permeability Cardiovascular physiology