This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'NK cells kill the viral infected cells due to: \nSelect and explain. \nA. Increased expression of MHC class I molecules, B. Decreased expression of MHC class I molecules, C. Increased expression of MHC class II molecules, D. Decreased expression of MHC class II molecules', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) Increased expression of MHC class I molecules Features of target cell killing by NK cell: Inversely related to target cell expression of MHC class I molecule. So, it kills the cell that expresses little or no HLA class I molecule (provide immunosurveillance) such as virus infected cells, ceain tumor cells and allogenic cells. Non-immune, i.e. without previous sensitization, MHC unrestricted and non-antibody mediated. It kills host cell infected with intracellular bacteria, e.g. Mycobacteria, TB. Listeria, monocytogens. Do not kill cells which express class I MHC (all normal nucleated cells express it).', 'role': 'assistant'}]