What is the primary role of natural killer (NK) cells?

• A. To produce antibodies
• B. To directly destroy infected or malignant cells
• C. To secrete cytokines
• D. To enhance the adaptive immune response

Answer: (B)

Natural killer (NK) cells play a fundamental role in the innate immune response by directly targeting and destroying infected or malignant cells. Unlike other immune cells that may primarily function by producing antibodies or enhancing the adaptive immune response, NK cells excel at identifying and eliminating cells that are stressed, infected by viruses, or transformed into cancerous cells.

They are equipped to recognize certain markers on these abnormal cells, which allows them to bind and initiate a process of cell lysis, effectively killing the undesired cells through mechanisms such as the release of cytotoxic granules containing perforin and granzymes. This rapid response is crucial for controlling infections and preventing the spread of tumor cells in the early phases of immune defense before adaptive immunity has been fully activated.

While NK cells do secrete cytokines and contribute indirectly to the adaptive immune response, those functions are secondary to their primary role of directly destroying compromised cells. This capacity makes them a key component in the body's immediate defense mechanisms against a variety of threats, including viral infections and tumors.