You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Natural killer cells attacks which of the following cells and explain in detail?
• The NK cells express activating and inhibitory receptors. The functional activity of the NK cells is regulated by a balance between signals from these receptors. Normal cells are not killed because inhibitory signals from normal MHC class I molecules override activating signals. The ability of NK cells to kill target cells is inversely related to target cell expression of MHC class I moleculesQ. If virus infection or neoplastic transformation disturbs or reduces the expression of class I MHC molecules, inhibitory signals delivered to NK cells are interrupted and lysis occurs.