The cytotoxic action of NK cells in antibody-dependent cellular cytotoxicity is mediated by which receptor interaction?

• A. CD28 co-stimulation
• B. TCR recognition
• C. BCR recognition
• D. Fc receptors engaging antibodies

Answer: (D)

In ADCC, the killer action of NK cells hinges on the Fc portion of antibodies bound to a target cell being recognized by Fc receptors on the NK cell surface. Specifically, NK cells express Fc gamma receptors (such as CD16) that bind the Fc region of IgG antibodies coating a target. This interaction cross-links receptors and sends activation signals inside the NK cell, triggering degranulation and the release of perforin and granzymes to kill the target.

This is why antibody-dependent cytotoxicity relies on Fc receptors engaging antibodies: without the antibody bound to the target, or without the NK cell Fc receptor, the NK cell would not be directed to attack. The other options involve T cell–related receptors or B cell receptors, which are not how NK cells mediate ADCC, and CD28 is a co-stimulatory signal for T cells, not NK cells.