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': 'NK cell marker is? \nSelect and explain. \nA. CD 34, B. CD 56, C. CD 1, D. CD 45', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., CD 56 * Virus infected cells and tumor (cancer) cells are killed by NK cells and cytotoxic T-cells Natural killer cells (NK cells)* These cells possess cytotoxic activity against virus infected cells, tumor cells and transplanted foreign cells.* Cytotoxicity of NK cells is neither antibody dependent nor MHC restricted. Activity is nonimmune as it does not require antigenic stimulation.* NK-cells are positive for CD 16 and CD56.* NK cells are usually negative for CD3, but a subset is positive for CD3 called NK/T-cells.* IL-2 acts as a growth factor for NK cells. NK cells activity is augmented by interferon. NK cells secrete peroforin (resembles complement C9) which causes transmembrane pores through which cytotoxic factors (e.g. TNF-(3) enters the cells and induce apoptosis.", 'role': 'assistant'}]