Integrins are the receptors that mediate cell adhesion to the extracellular matrix (ECM). They are involved in cell adhesion and recognition in a variety of processes including embryogenesis, hemostasis, tissue repair, immune response and metastatic diffusion of tumor cells. Integrin alpha-4 (ITGA4) is a receptor for fibronectin. ITGA4 functions as a heterodimer of an alpha subunit and the beta subunit of either the beta-1 chain or the beta-7 chain (ITGA4:ITGB1 shown here).

Natalizumab (Tysabri) is a humanised monoclonal antibody against the cell adhesion molecule α4-integrin. It is a medication used to treat multiple sclerosis and Crohn's disease (No authors 2004). It binds to the α4-subunit of α4b1 and α4b7 integrins expressed on the surface of all leukocytes except neutrophils, and inhibits the α4-mediated adhesion of leukocytes to their counter-receptors. This is thought to reduce the ability of inflammatory immune cells to attach to and pass through the cell layers lining the intestines and blood–brain barrier (Rice et al. 2005).