This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General pathology, Subject name: Pathology
[{'content': 'Which of the following statements best characterizes natural killer cells? \nSelect and explain. \nA. They are a subset of T cells, B. They are involved in type III hypersensitivity reactions, C. They require prior sensitization in order to kill virally infected cells or tumor cells, D. They paicipate in antibody-dependent cellular cytotoxicity reactions', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Natural killer (NK) cells account for 5% to 10% of lymphocytes. They paicipate in antibody dependent cellular cytotoxicity reactions (type II hypersensitivity reactions). NK cells are not T cells and are sometimes referred to as null cells. They can lyse virally infected cells and tumor cells without prior sensitization. NK cells are frequently referred to as large granular lymphocytes, and would not be confused with small B cells. When activated by interleukin-l, NK cells become lymphocyte-activated killer cells (LAK cells), which can be used to treat ceain cancers. NK cells are a source of gamma interferon, which induces class II expression and activates macroptIages.', 'role': 'assistant'}]