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 (reviewed in 1). Alpha 4 (?4) chain associates with either beta 1 (?1) or beta 7???7) chain. It has been demonstrated that the putative ligand-binding sites of both integrin ?4?1 and ?4?7 is located on the ?4 chain. These ligands included Madcam, VCAM, and fibronectin (2-4). Madcam is known as the principal ligand for integrin a4b7. Recently it was also demonstrated that HIV-1 envelope can mimic Madcam by binding to and signaling though integrin ?4?7, the gut mucosal homing receptor for peripheral T cells (5). This recombinant protein fragment includes the ligand and monoclonal antibody binding domains , this binding has been tested and verified in ELISA assays. This recombinant protein is recognized PSI antibodies Integrin 4? (IN1) (PSI 4827) and Integrin 4? (IN2) (PSI 4837), but not Integrin 4? (CT) (PSI 4783).