Integrins are heterodimer. These are divided into α and β subunits. Depending on the substructure of the β unit, there are five families, but for convenience β1 and β2 integrins are involved in leucocyte-endothelial interaction. β1 integrins, also known as very late activation proteins, are so named because they appear on lymphocytes several days after antigenic stimulation and are composed of a common β chain (CD29) paired with a different α chain. They mediate lymphocyte and monocyte binding to the endothelium receptors called vascular adhesion molecules. β2 integrins also have a common β chain (CD18), which pairs with different α chains (CD11 a,b,c) to form a number of separate molecules.These two sets of integrins mediate strong binding of leucocytes to the endothelial cell while β3-β5 are concerned with binding to extracellular matrix proteins such as fibronectin and vitronectin.