This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunity, Subject name: Pathology
[{'content': 'First line of defence against tumor and virus? \nSelect and explain. \nA. NK cell, B. T cell, C. Histiocyte, D. Macrophage', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ref: Robbins review E-Book, P 67* NK cells have the ability to respond without prior sensitization.* They carry receptors for MHC class I molecules which inhibit their lytic function. When expression of class I MHC molecules is reduced on a cell surface by viral interference, inhibitory receptors on NK cells do not receive a negative signal and the targeted cells is destroyed.* NK cells have CD16, Fc receptor that allows them to bind to opsonized cells and lyse them. This is a form of type II hypersensitivity with antibody mediated disease.', 'role': 'assistant'}]