The Ha2/5 monoclonal antibody specifically binds to the 130 kDa integrin β1 chain (CD29). CD29 is expressed on the cell surface as a heterodimer with one of the distinct integrin α chains. With α1 through α6 (CD49a through CD49f), it forms the VLA-1 through VLA-6 complexes, respectively, and with αV (CD51), it forms αVβ1 integrin. As a result, CD29 has a broad tissue distribution, including lymphocytes, endothelia, smooth muscle, and epithelia. The Ha2/5 hamster anti-rat CD29 monoclonal antibody cross-reacts with mouse thymocytes, splenocytes, and peripheral lymph node leukocytes. The Ha2/5 antibody blocks in vitro adhesion of CD29-expressing cells to collagen.