Leukocyte extravasation

Under a Leukodiapedese ( from Ancient Greek διά dia " through ", " round ", " between ", " apart ", and ancient Greek πηδᾶν pedantic "jump", " jumping ") refers to the passage of immune cells (monocytes, macrophages, granulocytes, lymphocytes ) through the inner lining (endothelium ) of small blood vessels ( arterioles, capillaries, and venules ). In case of heavy congestion and red blood cells (RBCs ) can escape. This form of diapedesis is called Erythrodiapedese.

Molecular Mechanism

Due to the inflammation pour tissue macrophages and dendritic cells from cytokines. These are mediator substances causing the endothelium of the blood vessels to the following reactions:

• Weibel- Palade bodies fuse with the cell membrane and provide adhesion molecules ( selectin P) on the surface.
• With a delay of several minutes to hours, selectin -E, CD31 and expressed the integrins ICAM -1 and VCAM -1.
• The endothelial cells pull themselves together and tight cell - cell junctions ( zonules occludens, " tight junctions " ) dissolve. Normally, these compounds prevent the leakage of plasma into the tissue. Now the plasma can escape, and it forms an edema.

Monocytes and neutrophils normally circulate in the blood. At the selectins, however, they remain (Similar to a tape) adhere and roll along the endothelium. Accordingly, we referred to this process as Rolling. With the integrins they enter into an even stronger bond, it is called adhesion. Chemokines, especially interleukin -8 are expressed on the proteoglycans of the endothelium and activate the adherent immune cells. This leads to a change in a factor called LFA -1 ( leukocyte function antigen). Now The altered LFA -1 binds very strongly to ICAM- 1 and can be activated via the actin cytoskeleton, the immune cell so that it begins with the Leukodiapedese. To this end, elastases, proteases and hyaluronidases are distributed, cut a hole in the basement membrane that lies beneath the endothelial cells and destroys the connective tissue to find a way through. Through this hole the immune cells migrate through. Along an IL- 8 gradient they find their way to the site of inflammation.

The Leukodiapedese is a highly complex process in which off- lead communication between mediators to changes in the cytoskeleton. The exact mechanism is still not elucidated. Many intracellular proteins such as profilin, gelsolin, thymosin and actin play a role. Also, the cells must protect its own catalytic enzymes. For this purpose, they carry receptors, for example, bind elastase in such a form that includes the active site of the cell membrane away.