**Core Concept**
NK cells, or natural killer cells, are a type of lymphocyte that play a crucial role in the innate immune system. They are capable of recognizing and killing infected cells or tumor cells without prior antigen exposure.

**Why the Correct Answer is Right**
NK cells express a variety of receptors on their surface, including the CD56 receptor, which is a marker of NK cell differentiation. The CD16 receptor, also known as FcγRIIIA, is another key receptor expressed on NK cells, which allows them to recognize and bind to IgG antibodies coating infected cells. This interaction between the CD16 receptor and the IgG antibody is crucial for NK cell activation and cytotoxicity.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because while NK cells do express CD3, it is a marker of T cell differentiation and not a characteristic of NK cells.
* **Option B:** This option is incorrect because while NK cells do express CD4, it is a marker of T helper cells and not a characteristic of NK cells.
* **Option C:** This option is incorrect because while NK cells do express CD8, it is a marker of cytotoxic T cells and not a characteristic of NK cells.

**Clinical Pearl / High-Yield Fact**
NK cells play a critical role in the innate immune response, particularly in the recognition and killing of infected cells or tumor cells. They can also be activated by cytokines such as IL-2 and IL-12, making them an important component of the adaptive immune response.

**Correct Answer: C. CD16**