The 9F10 monoclonal antibody specifically reacts with human CD49d, the 150 kDA alpha 4 integrin chain. The molecule forms the heterodimer called VLA-4 with integrin beta 1 and another heterodimer with integrin beta 7 that binds fibronectin, VCAM-1, and MadCAM-1. CD49d is expressed on monocytes, lymphocytes, thymocytes, NK cells, B cells, and T cells. It is involved in hematopoietic stem cell differentiation, cell migration, and cell activation. Its absence on Foxp3+ cells make it a useful marker to isolate Treg cell populations.