NCR1 and neoplasm: The ligands recognized by these receptors are either induced by stress (ligands for NKG2D, see [11], [16]), are viral proteins such as hemagglutinin (ligands for NKp44 and NKp46, see [17], [18]) and pp65 (ligands for NKp30, see [19]), are self-ligands [20] or are unknown tumor ligands.