CD 8 T Cells are activated by antigen presented by MHC I molecules on infected cells. As previously mentioned, many of our body cells can present MHC I since many are susceptible to various infections. The TCR will attach to the presented peptide, and the CD 8 coreceptor will attach to MHC I. Just like CD 4 cells, they will begin to proliferate and are also capable of secreting some cytokines such as IL-2, which helps them proliferate as well.
Their functions are a little less diverse than those of T Helper cells. Once activated, they are known as Cytotoxic T Cells (CTLs), and they will attach to an infected host cell via their TCR and MHC I and then initiate what is known as a "death pathway," leading to apoptosis. Two major apoptotic pathways can induce apoptosis: the perforin/granzyme pathway and the FAS/FAS L pathways. However, the first one is more common in CTLs. The release of granzyme and perforin induce a signal in the infected cell to self-destruct. The nucleus contracts and the entire cell eventually comes apart into membrane-bound blebs. Unlike necrosis, death by apoptosis is a "clean" cell death and does not induce an inflammatory response. Macrophages then clean up the debris. One CTL can kill many infected cells.
