Integrins are a family of dimeric, transmembrane proteins that mediate cell-cell and extracellular matrix adhesion. Signals transduced by integrins play a role in many biological processes, including cell growth, differentiation, migration and apoptosis. The integrin family is composed of at least 15 alpha and 8 beta subunits that may form over twenty different alpha-beta non-covalently bound dimeric combinations on the cell surface. The alpha subunits all have some homology to each other, as do the beta subunits. Both of the subunits contribute to the binding of the ligand. Integrin alpha subunits contain seven weak sequence repeats in the N-terminal region, which may be important in ligand binding, and have been predicted to fold cooperatively into a single beta-propeller domain with seven beta-sheets. In normal tissue, Integrin alpha-6/beta-1 is a receptor for laminin on human platelets. Integrin alpha-6/beta-4 is a receptor for laminin in epithelial cells and it plays a critical structural role in the hemidesmosome. Various disease states involving epithelial cells have been shown to be associated with alterations in alpha 6 integrin-containing heterodimers.