CD49e is a 135 kD protein, also known as alpha5 integrin or VLA-5 alpha chain. It is a member of the integrin family, expressed on thymocytes, splenic B cells, activated T cells, and mast cells. CD49e associates with CD29 (integrin beta1 chain) to form the fibronectin receptor (VLA-5). CD49e plays a critical role in both adhesion and T cell costimulation. The primary ligand for CD49e/CD29 (VLA-5) is fibronectin. The 5H10-27(MFR5) antibody has been shown to block CD49e mediated interactions and promote the in vitro stimulation of CD8+ T cells.