Molecular mechanism of Rolling, Adhesion and Emigration:

 Chemical mediators released during process, affect the process of rolling, adhesion, and emigration of leukocytes by regulating surface expression or affinity of adhesion molecules. Adhesion molecules involved belong to three molecular families as mentioned below:

1. Selectins:
 These are the receptors expressed on leukocytes and endothelium. It consists of:

a. E-selectin:
• Previously called ELAM-1
• Present on endothelium
• Binds to sialyl-lewis-X modified glycoproteins present on leukocytes.

b. L-selectins:
• Previously called LAM-1
• Present on leukocytes
• Binds to L-selectin ligand present on endothelium.

c. P-selectins:
• Present on endothelium and platelets
• Same as in E-selectin

2. Immunoglobins:
 These include two endothelial adhesion molecule: ICAM-1 (Intracellular adhesion molecule) and VCAM-1 (Vascular cell adhesion molecule). Both interact with integrins present on leukocytes.

3. Integrins:
 These are glycoproteins.
 Main integrin receptors for ICAM-1 are LFA-1 and MAC-1 and for VCAM-1 is VLA-4.