Which of the following statement is not true regarding NK cells
**Core Concept**
Natural Killer (NK) cells are a type of lymphocyte that plays a crucial role in the innate immune response, particularly in the recognition and elimination of virally infected cells and tumor cells. They are characterized by their ability to kill target cells without prior antigen exposure.
**Why the Correct Answer is Right**
NK cells recognize and destroy target cells through a complex interplay of activating and inhibitory receptors. Activating receptors, such as NKG2D, recognize stress-induced ligands on the surface of target cells, while inhibitory receptors, like KIRs, recognize MHC class I molecules. The balance between these signals determines whether the NK cell will respond to the target cell. In the case of NK cells, they can kill target cells through the release of cytotoxic granules, including perforin and granzymes.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because NK cells do not require prior antigen exposure to recognize and destroy target cells.
**Option B:** This option is incorrect because NK cells can recognize and destroy tumor cells, but they do not require MHC class II presentation.
**Option C:** This option is incorrect because NK cells can recognize and destroy virally infected cells through the recognition of stress-induced ligands, such as MICA and MICB.
**Clinical Pearl / High-Yield Fact**
NK cells are an important component of the innate immune response, and their dysregulation has been implicated in various diseases, including cancer and autoimmune disorders. Understanding the mechanisms of NK cell function is crucial for the development of immunotherapies and cancer treatments.
**Correct Answer: A. NK cells do not require prior antigen exposure to recognize and destroy target cells.**