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': 'The earliest feature of tuberculosis is \nSelect and explain. \nA. Caseation, B. Granuloma formation, C. Formation of giant cells (Langhans), D. Recruitment of lymphocytes', 'role': 'user'}, {'content': 'Answer: D \nExplanation: • Macrophages are the primary cells infected by M. tuberculosis. Early in infection, tuberculosis bacilli replicate essentially unchecked, while later in infection, the cell response stimulates macrophages to contain the proliferation of the bacteria.\n• About 3 weeks after infection, a T-helper 1 (TH1) response is mounted that activates macrophages to become bactericidal.\n• The TH1 response orchestrates the formation of granulomas and caseous necrosis. Macrophages activated by IFN-γ\ndifferentiate into the “epithelioid histiocytes” that characterize the granulomatous response, and may fuse to form giant cells.', 'role': 'assistant'}]