**Core Concept**
The tuberculin test, also known as the Mantoux test, is a diagnostic tool used to assess the immune response to Mycobacterium tuberculosis infection. It involves the intradermal injection of purified protein derivative (PPD) tuberculin, which elicits a delayed-type hypersensitivity reaction in individuals who have been previously exposed to the bacteria.

**Why the Correct Answer is Right**
The tuberculin test relies on the principle of cell-mediated immunity, where T lymphocytes, particularly those of the T-helper 1 (Th1) subset, recognize and respond to the PPD antigens. This leads to the activation of macrophages and the release of cytokines, resulting in the characteristic induration and erythema observed in the test. The reaction is typically measured after 48-72 hours and is considered positive if the induration is ≥ 10 mm in diameter.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the tuberculin test, which is a diagnostic tool for tuberculosis infection, not a treatment or vaccine.
**Option B:** While the tuberculin test does involve a type of hypersensitivity reaction, it is not a type I hypersensitivity reaction, which is characterized by the release of histamine and other mediators from mast cells.

**Clinical Pearl / High-Yield Fact**
The tuberculin test is a useful tool for diagnosing latent tuberculosis infection, but it can be affected by various factors, including previous BCG vaccination, which can result in a false-positive reaction.

**Correct Answer:** C. Delayed-type hypersensitivity reaction