Type IV (Cell Mediated) Hypersensitivity- Mechanism and Examples


Hypersensitivity is a term used to describe an abnormal or excessive immune response to a foreign substance or antigen. Hypersensitivity reactions can be classified into four types based on the mechanism and the time course of the reaction.

Type IV hypersensitivity, also known as delayed type hypersensitivity or cell mediated hypersensitivity, is a type of immune reaction that involves the activation of T cells and macrophages. Unlike the other types of hypersensitivity, which are mediated by antibodies, type IV hypersensitivity does not involve antibodies or complement. Instead, it is triggered by antigens that are either presented by antigen-presenting cells (APCs) or bound to body proteins.

Type IV hypersensitivity is characterized by a delayed onset of symptoms, usually 24 to 72 hours after exposure to the antigen. The symptoms are caused by the release of inflammatory cytokines and the recruitment of other immune cells to the site of antigen exposure. The inflammation can result in tissue damage and chronic diseases.

Type IV hypersensitivity can be caused by various types of antigens, such as intracellular pathogens (e.g., Mycobacterium tuberculosis, Listeria monocytogenes), contact allergens (e.g., nickel, poison ivy), or self-antigens (e.g., in autoimmune diseases). Some examples of type IV hypersensitivity reactions are the tuberculin reaction, granuloma formation, allergic contact dermatitis, and type-1 diabetes.

In this article, we will discuss the mechanism and variants of type IV hypersensitivity and provide some examples of this type of immune response. We will also explain how type IV hypersensitivity can be diagnosed and treated.