CD82 is a 45-90 kD type III tetraspan membrane protein which is encoded by the KAI1 gene. A member of the 4-span transmembrane protein superfamily (TM4SF) CD82 forms a complex with CD37, CD53, CD81, ECM and MHC molecules. CD82 is expressed on monocytes, granulocytes, lymphocytes, epithelial cells, endothelial cells, and fibroblasts and plays a role in signal transduction and adhesion. It has been suggested CD82 functions as a tumor suppressor as loss of expression has been found to promote tumor metastasis.