This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Pathology
[{'content': 'All of the following statements about NK cells are true except: \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 cells are innate immune cells They are functional without prior activation and do not express highly variable and clonally distributed receptors for antigens. NK cells have two types of receptors-- Inhibitory and Activating. They are capable of MHC - unrestricted direct cell lysis which is not mediated by an immune response.', 'role': 'assistant'}]