Example of Type IV Hypersensitivity is/are
**Core Concept**
Type IV hypersensitivity is a delayed-type immune response mediated by T lymphocytes, specifically T helper 1 (Th1) cells and cytotoxic T cells. This type of hypersensitivity reaction involves the activation of immune cells, such as macrophages and eosinophils, leading to tissue damage and inflammation.
**Why the Correct Answer is Right**
The correct answer involves the mechanism of cell-mediated immunity, where T cells recognize and respond to antigens presented by antigen-presenting cells (APCs). This recognition triggers the release of cytokines and other signaling molecules, which activate immune cells and lead to the characteristic delayed-type hypersensitivity reaction. Type IV hypersensitivity is responsible for various conditions, including contact dermatitis, tuberculin reaction, and graft-versus-host disease.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Type I hypersensitivity is mediated by IgE antibodies and mast cells, not T lymphocytes.
**Option B:** This option is incorrect because Type II hypersensitivity involves antibodies directed against cell surface or tissue antigens, leading to complement activation and cell destruction.
**Option C:** This option is incorrect because Type III hypersensitivity involves the formation of immune complexes, which deposit in tissues and activate the complement system.
**Clinical Pearl / High-Yield Fact**
Remember that Type IV hypersensitivity reactions are often referred to as "delayed" reactions, as they occur 48-72 hours after antigen exposure. This is in contrast to Type I hypersensitivity reactions, which occur immediately upon antigen exposure.
**Correct Answer:** C.