Adhesion Molecules

Figure 1: Schematic representation of the stages of migration of leucocytes from the circulation to an area of injury observable on microscopy. a) denotes the normal situation. In b) the leucocytes are seen to roll along the endothelium, they appear `sticky'. In c) the leucocytes are tightly adherent to the endothelium and in d) they migrate through the endothelium into the interstium. In the transmigration stage there are gaps formed between the endothelial cells and in the underlying basment membrane.

The movement of leucocytes from the circulation to an area of injury is visible on microscopy and goes through several stages in an orderly manner, see figure 1. The interaction of leucocytes with the endothelium is controlled by several families of molecules. These are the selectins, members of the immunoglobulin superfamily and integrins. (Table 1).

Table 1: The most common adhesion molecules involved in leucocyte endothelial interactions

Name	Molecular weight	Location	Function
Selectins
L-selectin (CD62L, LAM-1, LECAM-1)	150	Monocytes, B, T and NK cells	Binds to CD34, Glycam mediated leucocyte rolling
E-selectin (CD62E, ELAM-1)	140	Endothelium	Binds to Sialy Lewis x, mediated leucocyte rolling
P-selectin (CD62P, PADGEM)	140	Platlets and Endothelium	Mediating rolling and adhesion
Integrins
CD11a/CD18 (LFA-1)	180/95	All leucocytes	Binds to ICAM-1, ICAM-2 and ICAM-3
CD11b/CD18 (Mac-1)	170/95	Myeloid, NK cells, leucocytes	Binds to ICAM-1, C3b, extracellular matrix protein
CD11c/CD18 (CR4, P150,95)	150/95	Myeloid cells, leucocytes	Binds to fibrinogen
Immunoglobulins
ICAM-1 (CD54)	75-115	Haemopoietic and non haemopoietic cells	Binds to CD11a/CD18 and CD11b/CD18
ICAM-2 (CD102)	55-65	Resting lymphocytes, Monocytes, Endothelial cells	Binds to CD11a/CD18
ICAM-3 (CD50)	130	Thymocytes, leucocytes	Binds to CD11a/CD18
VCAM-1 (CD1O6)	100, 110	Endothelium	Ligand for VLA-4
PECAM-1 (CD31)		Endothelium, platlets and leucocytes