The integrin alpha 4 (also known as CD49d and ITGA4) belongs to the integrin alpha chain family of proteins. Integrins are heterodimeric integral membrane proteins composed of an alpha and beta chains. Alpha4 chain associates with either beta1 or beta7 chain. It has been demonstrated that the putative ligand-binding sites of both integrin alpha4beta1 and alpha4beta7 is located on the alpha4 chain. These ligands included Madcam, VCAM, and fibronectin. Madcam is known as the principal ligand for integrin alpha4beta7. Recently it was also demonstrated that HIV-1 envelope can mimic Madcam by binding to and signaling though integrin alpha4beta1, the gut mucosal homing receptor for peripheral T cells. At least two isoforms are known to exist.