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
All of the following statements about NK cells are true except: 
Select and explain. 
A. 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
C: They are MHC restricted cytotoxic cells
Answer: C: They are MHC restricted cytotoxic cells 
Explanation: 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.