Which cells are responsible for recognizing and attacking tumor cells lacking MHC-I expression?

Which cells are responsible for recognizing and attacking tumor cells lacking MHC-I expression?

• A. T cells
• B. Macrophages
• C. Natural killer cells
• D. B cells

Answer: (C)

Natural killer (NK) cells play a crucial role in the immune system's surveillance against tumor cells that may downregulate or completely lack the expression of MHC-I molecules. In a healthy situation, normal body cells present MHC-I on their surface, which allows cytotoxic T cells to recognize and eliminate infected or malignant cells. However, some tumor cells evade detection by reducing or losing MHC-I expression, making them less visible to T cells. NK cells are part of the innate immune system and are uniquely able to recognize these cells lacking MHC-I without prior sensitization to tumor antigens. They possess activating receptors that engage with stress molecules or other ligands often upregulated on tumor cells during malignancy. Additionally, NK cells have inhibitory receptors that recognize MHC-I. When MHC-I is absent, the inhibitory signals are not provided, allowing the NK cells to initiate cytotoxic responses against the tumor cells. This innate immune mechanism is essential for controlling tumor growth and providing a first line of defense, particularly in instances where adaptive responses (like T cell-mediated immunity) may not be effective due to the cancer cell’s evasion tactics.

Natural killer (NK) cells play a crucial role in the immune system's surveillance against tumor cells that may downregulate or completely lack the expression of MHC-I molecules. In a healthy situation, normal body cells present MHC-I on their surface, which allows cytotoxic T cells to recognize and eliminate infected or malignant cells. However, some tumor cells evade detection by reducing or losing MHC-I expression, making them less visible to T cells.

NK cells are part of the innate immune system and are uniquely able to recognize these cells lacking MHC-I without prior sensitization to tumor antigens. They possess activating receptors that engage with stress molecules or other ligands often upregulated on tumor cells during malignancy. Additionally, NK cells have inhibitory receptors that recognize MHC-I. When MHC-I is absent, the inhibitory signals are not provided, allowing the NK cells to initiate cytotoxic responses against the tumor cells.

This innate immune mechanism is essential for controlling tumor growth and providing a first line of defense, particularly in instances where adaptive responses (like T cell-mediated immunity) may not be effective due to the cancer cell’s evasion tactics.