Question

NK cells are immunologically significant as they recognize and kill:

• A. intracellular bacteria reservoirs.
• B. cells with upregulated MHC-I molecules.
• C. cells with downregulated MHC-I molecules.
• D. cells with self-marker on their surface.

Hint:

NK cells = "Missing Self" detectors.

Answer 1

The Correct Option is C

Step 1: Concept
Natural Killer (NK) cells are part of the innate immune system and provide "missing-self" recognition.

Step 2: Meaning
Major Histocompatibility Complex I (MHC-I) is expressed on almost all nucleated cells to signal that they are "self."

Step 3: Analysis
Many viruses and cancer cells try to evade T-cells by downregulating (decreasing) MHC-I expression. NK cells have inhibitory receptors that specifically look for MHC-I; if the MHC-I levels are low or absent, the inhibitory signal is lost, and the NK cell kills the target.

Step 4: Conclusion
NK cells detect and eliminate cells that have lost their normal MHC-I markers. Final Answer: (C)