Antigenic structures recognized by cytotoxic T lymphocytes

cells, through antibody molecules embedded in their cell surface membrane, collectively recognize an enormous diver- sity of antigens in solution or on cell surfaces, including native and unfolded proteins, peptides, polysaccharides, nucleic acids, steroids, and small organic molecules. The antigen- specific receptors on T cells are very similar to antibodies structurally and in the genetic basis for their diversity. Never- theless, the antigenic structures recognized by T cells consist almost exclusively of peptides associated with integral mem- brane glycoproteins known as MHC’ proteins (because they are encoded in a genetic region called the major histocompat- ibility complex). Thus T cells recognize protein antigens in a fragmented (or “processed”) form on the surface of other cells expressing appropriate MHC molecules (a phenomenon termed MHC “restriction” of the T cell response