FIGURE 1.

Activation–inhibition and molecules of major histocompatibility complex, class i (mhc-i). Tumours are killed either when they are able to express mhc-i molecules containing tumour peptide antigens recognized by the rearranging T-cell receptor (tcr) of cytotoxic T lymphocytes (ctls), or when self–mhc-i molecules are lacking or unable to properly engage non-rearranging inhibitory receptors, mainly (but not exclusively) expressed by natural killer (nk) cells. Peptide antigens must be processed and tailored before they can stabilize mhc-i assemblies with β₂-microglobulin (β₂m). Only folded mhc-i molecules serve as ligands of ctls and nk cells.