CD49d is a 150 kD glycoprotein, also known as alpha4 integrin or VLA-4 alpha chain. It is a member of the integrin family, expressed on T and B cells, monocytes, eosinophils, basophils, mast cells, thymocytes, NK cells, and dendritic cells. CD49d is a heterodimer expressed with either of two beta chains, beta1 (CD29) or beta7, to form the VLA-4 (integrin alpha4beta1) or LPAM-1 (integrin alpha4beta7) complexes. CD49d plays a critical role in both adhesion and T cell costimulation. The primary ligands for CD49d are VCAM-1, MAdCAM-1, and fibronectin. The 9C10(MFR4.B) antibody, in combination with the R1-2 monoclonal antibody, completely blocks VCAM-1 binding to VLA-4.