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': 'False statement about NK (natural killer) cells: \nSelect and explain. \nA. They are derived from large granular cells, B. They comprise about 5% of human peripheral lymphoid cells, C. They are MHC restricted cytotoxic cells, D. They express IgG Fc receptors', 'role': 'user'}, {'content': 'Answer: C \nExplanation: NK cell cytotoxicity is the nonimmune, MHC-unrestricted, non-antibody-mediated killing of target cells, which are usually malignant cell types, transplanted foreign cells, or virus-infected cells. NK cells account for ~5-15% of peripheral blood lymphocytes. NK cells express surface receptors for the Fc poion of IgG. They are derived from large granular cells. Ref: Harrisons principles of internal medicine, 18th edition, chapter: 314', 'role': 'assistant'}]