Tuberculin test is a delayed hypersensitivity (Type IV) to intradermal injection of purified protein derivative (PPD) of Tuberculin, to test for cell mediated immunity against Mycobacteria. 

• The tuberculin test is based on the fact that infection with M. tuberculosis produces sensitivity to certain antigenic components of the organism that are contained in culture extracts called "tuberculins.
• " Hypersensitivity to tuberculin, which is demonstrated by the development of a positive reaction to the tuberculin skin test, develops 2 to 10 wk after the initial infection.

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