CD104 is a 205 kD type I transmembrane glycoprotein, also known as integrin β4 chain or β4 integrin, that associates with integrin α6 (CD49f) to form the α6/β4 (CD49f/CD104) heterodimer. CD104 is expressed on epithelial cells (especially on proliferative basal layer epithelial cells in skin), endothelial cells, Schwann cells, certain tumor cells, and a subset of pre-T cells. The CD49f/CD104 heterodimer is an adhesion receptor for laminins (especially laminin 5) and keratin filaments, and is involved in the regulation of hemidesmosome formation and cell proliferation and activation.