What role do NK cells play in the context of cancer?

• A. They promote tumor growth
• B. They destroy tumor cells without prior sensitization
• C. They create antibodies against cancer cells
• D. They signal other immune cells to attack

Answer: (B)

Natural Killer (NK) cells play a crucial role in the immune response against cancer by directly identifying and destroying tumor cells without the need for prior sensitization. This characteristic is a key feature of NK cells, as they are part of the innate immune system. Unlike T cells, which require recognition of specific antigens presented by Major Histocompatibility Complex (MHC) molecules, NK cells can recognize stressed or infected cells, including many tumor cells, through various activating receptors.

NK cells are equipped with the ability to detect signs of abnormality on the surface of cells, such as the reduced expression of MHC class I molecules, which is often a characteristic of cancer cells. Upon recognizing these features, NK cells can initiate apoptosis (cell death) in the impacted tumor cells by releasing cytotoxic granules containing perforin and granzymes.

This direct cytotoxic action is vital in the context of cancer because it enables early and swift responses to emerging tumors without needing previous exposure to specific tumor antigens, allowing the immune system to act quickly in targeting malignant cells. Other functions of NK cells, such as signaling other immune cells to mount a more coordinated attack, are secondary to their primary role of directly eliminating tumor cells.