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. Alpha 4 chain associates with either beta 1 or beta 7 chain. It has been demonstrated that the putative ligand-binding sites of both integrin alpha 4 beta 1 and alpha 4 beta 7 is located on the alpha 4 chain. These ligands included Madcam, VCAM, and fibronectin. Madcam is known as the principal ligand for integrin alpha 4 beta 7. Recently it was also demonstrated that HIV-1 envelope can mimic Madcam by binding to and signaling though integrin alpha 4 beta 7, the gut mucosal homing receptor for peripheral T cells. 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 alpha (IN1) (PSI 4827) and Integrin 4 alpha (IN2) (PSI 4837), but not Integrin 4 alpha (CT) (PSI 4783).