This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'Cell-mediated immunity is- \nSelect and explain. \nA. Type I, B. Type II, C. Type III, D. Type IV', 'role': 'user'}, {'content': "Answer: D \nExplanation: Cell-mediated (Type) hypersensitivity\n\nIt is initiated by activated\xa0T-lymphocytes.\n\nIt includes\n1. Delayed-type hypersensitivity - mediated by CD-4 T cells.\n2. T-cell mediated cytotoxicity - mediated by CDS- T cells.\n1. Delayed-type hypersensitivity\n\nIn delayed hypersensitivity reactions,\xa0CD-4 T cells and macrophages are primarily involved.\nThe term delayed is used to differentiate\xa0it from a secondary' cellular response, which appears at\xa048-72 hours after antigen\xa0exposure and from an immediate hypersensitivity\xa0response, which generally appears within minutes,\nDelayed hypersensitivity is a major mechanism of defence against various intracellular pathogens, including mycobacteria, fungi and certain parasites.\n\nPathophysiology\n\nDelayed hypersensitivity\xa0is characterized by the formation\xa0of granuloma - a localized mass that\xa0contains activated\xa0macrophages (epithelioid)\xa0cells surrounded by colour of lymphocytes and\xa0giant cells.\nIt is also called granulomatous Inflammation.\nThe cellular events start when an antigen (eg tuberculin antigen) on antigen presenting cell comes\xa0in contact with naive CD-4 T cells → naive CD-4 T cells recognize this peptide antigen in\xa0association with MHC – II and differentiate into T4-l cells.\nInduction of T4-l cells is of central importance because the expression of delayed\xa0hypersensitivity largely depends on the cytokines secreted by T4-l cells.\n\n2. T-cell mediated cytotoxicity\n\nIn this type of hypersensitivity, cytotoxic T cells kill virus-infected or tumor cells.", 'role': 'assistant'}]