A 9 year old girl receives an intradermal tuberculin injection and later develops an indurated, erythematous papule 12 mm in diameter. This reaction is an example of which of the following?

**Core Concept**
The question tests the understanding of **cell-mediated immunity** and **hypersensitivity reactions**, specifically the response to a tuberculin injection, also known as a Mantoux test. This reaction is a form of **delayed hypersensitivity**.

**Why the Correct Answer is Right**
The correct answer is related to the type of hypersensitivity reaction characterized by the involvement of T cells, which play a crucial role in cell-mediated immunity. The indurated, erythematous papule that develops is a result of the immune response to the tuberculin, indicating previous exposure to **Mycobacterium tuberculosis**.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it represents an immediate hypersensitivity reaction.
**Option B:** Incorrect as it is not directly related to the immune response described.
**Option C:** Incorrect because, although it involves immune complexes, it doesn't accurately describe the reaction to the tuberculin test.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the size of the induration, not the erythema, is used to interpret the result of the tuberculin skin test, with larger diameters indicating a positive result.

**Correct Answer:** D. Type IV hypersensitivity reaction.

✓ Correct Answer: D. Type IV hypersensitivity