CD8 (cluster of differentiation 8), also known as Lyt-2, Ly-2, is a surface glycoprotein comprising of α and β chains and is primarily expressed on immature thymocytes, mature CD8 T cells and some other cell types, e.g., dendritic cells. CD8 exist as either α/β heterodimer in most thymocytes or α/α homodimer on a subset ofγ/δ TCR-bearing intraepithelial lymphocytes. CD8 is an antigen co-receptor on T cells that associates with the T cell receptor complex during antigen presentation through MHC class I by APC cells. This antibody recognizes the 34 kDa CD8 α chain on the cell surface.