**Core Concept**
Delayed hypersensitivity reaction, also known as type IV hypersensitivity, is a cell-mediated immune response that occurs when T lymphocytes recognize and react to specific antigens. This type of reaction is characterized by a delayed onset, typically occurring 48-72 hours after antigen exposure.

**Why the Correct Answer is Right**
The correct answer is a type of T lymphocyte that plays a crucial role in the cell-mediated immune response. Specifically, **Option C: T helper 1 (Th1) cells** are involved in the activation of macrophages and the release of cytokines, which contribute to the inflammatory response and tissue damage associated with delayed hypersensitivity reactions. Th1 cells recognize and bind to antigens presented by antigen-presenting cells, leading to the activation of immune cells and the production of pro-inflammatory cytokines.

**Why Each Wrong Option is Incorrect**
**Option A:** T helper 2 (Th2) cells are primarily involved in the humoral immune response and the activation of B cells, rather than the cell-mediated immune response.
**Option B:** Cytotoxic T cells are involved in the direct killing of infected cells or tumor cells, rather than the activation of immune cells through the release of cytokines.

**Clinical Pearl / High-Yield Fact**
Delayed hypersensitivity reactions are often seen in conditions such as tuberculosis, leprosy, and contact dermatitis, where the immune system reacts to specific antigens.

**Correct Answer:** C. T helper 1 (Th1) cells.