PPD skin test, after 48 hours, 15 mm zone is due to

PPD skin test, after 48 hours, 15 mm zone is due to

• A. B cell
• B. Macrophage
• C. T cell
• D. Neutrophil

Answer: (C)

Delayed-type hypersensitivity from a PPD test is driven by sensitized T lymphocytes. When the purified protein derivative is introduced into the skin, memory Th1 cells that have seen mycobacterial antigens release cytokines (like IFN-γ) that activate and recruit macrophages to the site. The activated macrophages mediate the local inflammation and induration seen at about 48 hours. So the reaction is T cell–mediated, with macrophages as the recruited effector cells, rather than being driven primarily by B cells or neutrophils.

Delayed-type hypersensitivity from a PPD test is driven by sensitized T lymphocytes. When the purified protein derivative is introduced into the skin, memory Th1 cells that have seen mycobacterial antigens release cytokines (like IFN-γ) that activate and recruit macrophages to the site. The activated macrophages mediate the local inflammation and induration seen at about 48 hours. So the reaction is T cell–mediated, with macrophages as the recruited effector cells, rather than being driven primarily by B cells or neutrophils.