What happens if a cell does not express MHC-I?

• A. Likely eliminated by NK cells
• B. It will be targeted by antibodies
• C. It will become a B cell
• D. It will secrete interferon

Answer: (A)

Missing self recognition is how NK cells detect trouble. Normal cells express MHC class I, which engages inhibitory receptors on NK cells and prevents them from killing. When a cell loses MHC I expression (a common tactic of some viruses and tumors), those inhibitory signals vanish. Activating receptors on NK cells then drive their response, and they release perforin and granzymes to kill the target. So, a cell without MHC I is targeted by NK cells. This isn’t because it becomes a B cell, nor is it something directly caused by antibody targeting or interferon secretion—the primary outcome here is NK cell–mediated destruction due to the loss of inhibitory signaling.