CD8 is a glycoprotein found on the surface of certain immune cells, specifically T cells. It plays a crucial role in the immune response by helping these cells recognize and bind to infected or cancerous cells. CD8+ T cells, also known as cytotoxic T cells, are essential for identifying and destroying cells that display abnormal proteins. When a virus infects a cell, it presents pieces of the virus on its surface. CD8+ T cells use their CD8 protein to interact with these infected cells, leading to their activation. Once activated, they can kill the infected cells, helping to eliminate the infection and protect the body.