ABSTRACT
Integrins are a family of cell surface receptors that are expressed on virtually every cell in complex multicellular organisms. Each member of this family is a heterodimeric transmembrane protein made up of an and subunit that assemble noncovalently (1,2). In humans, there are at least 18 and 8 subunits that have been shown to associate to form at least 24 receptors (Fig. 1). Integrins share in common the ability to detect and respond to ligands that are spatially restricted to the extracellular space, but there is a remarkable biochemical diversity of integrin ligands. Some complexes, such as the epithelial-restricted integrin, v6, or the platelet integrin, IIb3, are unique to specific cell types, whereas other complexes are widely expressed (3,4).
