The monoclonal antibody NKI-SAM1 reacts with human CD49e, also known as integrin α5 chain. Integrins are cell-surface receptors, expressed as heterodimers essential in various processes mediating intercellular or cellmatrix interaction. Integrin α5 is composed of a heavy and a light chain linked by a disulfide bond. CD49e associates non-covalently with the integrin ß1 (CD29) forming the very late activation antigen-5 (VLA5) complex which is expressed on many cell types including peripheral lymphocytes, monocytes, fibroblasts, and endothelial cells and is a receptor for fibronectin and fibrinogen but functions also as a receptor for laminin and several other extracellular matrix proteins.