The monoclonal antibody 5H10-27 reacts with the alpha5 chain (VLA-5) of the CD49e/CD29 heterodimeric fibronectin receptor. It is expressed on thymocytes, activated T cells, mast cells, and a variety of mouse cell lines.1-5 Soluble 5H10-27 antibody inhibits VLA-5-mediated functions in vitro.1, 2-4, 6 Immobilized 5H10-27 has also been demonstrated to co-stimulate the proliferative response of CD8+ T cells to plate-bound anti- CD3 monoclonal antibody.3