Integrin alpha 4 beta 7 is an integrin family adhesion receptor that shares subunits with alpha 4 beta 1 (VLA4) and the E-Cadherin receptor, alpha E beta 7 (1). It is a non-covalent heterodimer composed of two type I transmembrane glycoprotein subunits, a 150 kDa alpha 4 (CD49d) subunit and a 130 kDa beta 7 subunit (2, 3). The alpha 4 extracellular domain (ECD) contains an N-terminal beta -propeller structure followed by thigh, calf-1, and calf-2 domains (1). The beta 7 ECD contains a vWFA domain, which interacts with the
alpha 4 beta -propeller to form a binding domain. Metal ion binding sites termed MIDAS and LIMBS promote firm adhesion, and another site termed ADMIDAS is a negative regulatory site that promotes rolling (4-6). The mouse alpha 4 ECD shares 94% and 85% amino acid sequence identity with the rat and human alpha 4 ECD, respectively. The mouse beta 7 ECD shares 94% and 87% amino acid sequence identity with the rat and human beta 7 ECD, respectively. Integrin alpha 4 beta 7 binds the mucosal addressin
MAdCAM-1, as well as VCAM-1 and Fibronectin (7). Integrin alpha 4 beta 7, which is critical for homing to intestinal mucosa, is induced during T cell activation in Peyer’s patches or mesenteric lymph nodes (8, 9). Its expression requires signals from local dendritic and stromal cells, including secreted retinoic acid (10, 11). The HIV-1 envelope protein gp120 binds to the active form of Integrin alpha 4 beta 7, and this may or may not account for the concentration of HIV-1 virus in the gut-associated lymphoid tissue (GALT) (12-14). Integrin alpha 4 beta 7 may also be involved in lymphocyte trafficking in acute intestinal graft vs. host disease (GVHD) (15).