Which statement about innate immune responses to tumors is true?

• A. NK cell-mediated apoptosis.
• B. MHC I-restricted T-cell-mediated destruction.
• C. ADCC.
• D. All of the above.

Answer: (A)

Innate tumor surveillance relies on natural killer cells, which can detect transformed cells that often have reduced MHC class I expression or display stress-induced ligands. Because NK cells do not require antigen-specific sensitization, they provide an immediate, innate response. Once activated, NK cells induce target cell death by releasing perforin and granzymes to trigger apoptosis, and they can also use death receptor pathways. They also secrete cytokines like interferon-gamma to boost other immune responses. In contrast, destroying tumor cells through MHC I–restricted T cells depends on antigen-specific CD8+ T cells, a hallmark of adaptive immunity. ADCC involves antibodies bound to tumor cells and recruitment of effector cells via Fc receptors, which relies on antibodies produced by the adaptive system, so it’s not a pure innate mechanism. Therefore, NK cell–mediated apoptosis best describes the innate response to tumors.