Langhans giant cells are formed by the fusion of which cells?

• A. Neutrophils
• B. Activated macrophages fuse to form Langhans giant cells.
• C. B cells
• D. Epithelial cells

Answer: (B)

Langhans giant cells form when activated macrophages fuse together, a process that occurs in granulomatous inflammation such as tuberculosis. Monocyte-derived macrophages are activated by cytokines, especially IFN-γ from Th1 cells, and then fuse to create a multinucleated cell with nuclei arranged in a horseshoe or peripheral ring. This makes activated macrophages the correct source of Langhans giant cells. Neutrophils, B cells, and epithelial cells do not form Langhans giant cells (neutrophils are short-lived phagocytes, B cells are lymphocytes that don’t fuse to giant cells, and epithelial cells can form other multinucleated syncytia in some contexts but not Langhans giant cells).