The PS/2 monoclonal antibody reacts with human and mouse VLA-4 α chain also known as CD49d and integrin alpha 4. VLA-4 is a 150 kDa glycoprotein belonging to the integrin family that is expressed by many cell types including T and B lymphocytes, monocytes, eosinophils, basophils, mast cells, thymocytes, NK cells, and dendritic cells. Integrin α4 associates with integrin β7 to form integrin α4β7 also known as LPAM-1 as well as integrin β1 (CD29) to form integrin α4β1 also known as VLA-4. Integrin α4 plays roles in adhesion and T cell co-stimulation. Integrin α4 ligands include VCAM-1, MAdCAM-1, and fibronectin. The PS/2 antibody is useful for in vivo and in vitro VLA-4 neutralization.