Final answer:
CD8 binds to the α1 and α2 domains of MHC class I, which form the antigen-binding cleft.
Step-by-step explanation:
The student asked: To which domain of MHC class I does CD8 bind? CD8 is a co-receptor found on the surface of cytotoxic T cells. In the context of immune response, CD8+ T cells bind to MHC class I molecules, which are expressed on all nucleated cells in the body. The specific domains of the MHC class I molecule that CD8 binds to are the α1 and α2 domains, which together form the antigen-binding cleft of MHC I. It is this interaction that is key for the cytotoxic T cells to recognize and kill cells infected with intracellular pathogens.