## **Core Concept**
The Mantoux test, also known as the Tuberculin Skin Test (TST), is a diagnostic tool used to assess if a person has been infected with *Mycobacterium tuberculosis*. It involves the intradermal injection of purified protein derivative (PPD) tuberculin. The test relies on the body's immune response to the tuberculin.

## **Why the Correct Answer is Right**
The Mantoux test is based on **delayed-type hypersensitivity (DTH)**, also known as cell-mediated immunity. This type of hypersensitivity reaction involves T lymphocytes, which recognize and respond to the tuberculin antigen. The reaction is characterized by induration (hardening) and erythema (redness) at the injection site, which is measured after 48-72 hours. A positive reaction indicates that the individual has been exposed to *M. tuberculosis* and has developed cell-mediated immunity.

## **Why Each Wrong Option is Incorrect**
- **Option A: Immediate hypersensitivity** is incorrect because it involves IgE antibodies and is associated with allergic reactions such as anaphylaxis, urticaria, and allergic rhinitis. This does not apply to the Mantoux test.
- **Option B: Cytotoxic hypersensitivity** is incorrect because it involves the direct action of antibodies or complement against cells, leading to cell destruction. This mechanism is not relevant to the Mantoux test.
- **Option D: Autoimmune hypersensitivity** is incorrect because it involves the immune system reacting against the body's own tissues. The Mantoux test is not related to autoimmune reactions.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the Mantoux test can yield false-negative results in individuals with severe tuberculosis, those with compromised immune systems (e.g., HIV/AIDS, corticosteroid therapy), and very young children. Conversely, false-positive results can occur in individuals who have been vaccinated with BCG (Bacillus Calmette-Guérin) or those exposed to non-tuberculous mycobacteria.

## **Correct Answer: C. Delayed type hypersensitivity**