Type IV hypersensitivity

Definition

Type IV hypersensitivity, also known as delayed-type hypersensitivity, is an immune response mediated by T cells rather than antibodies, leading to inflammation and tissue damage several hours to days after exposure to an antigen. This type of reaction is crucial in the defense against intracellular pathogens but can also contribute to chronic inflammatory conditions and autoimmune diseases.

5 Must Know Facts For Your Next Test

1. Type IV hypersensitivity reactions are characterized by a delayed response, typically occurring 24 to 48 hours after exposure to the allergen or antigen.
2. Common examples include contact dermatitis from poison ivy or nickel, tuberculin skin tests (like the Mantoux test), and graft-versus-host disease.
3. The immune response involves the activation of CD4+ T helper 1 (Th1) cells and CD8+ cytotoxic T cells, leading to the recruitment of macrophages to the site of exposure.
4. This type of hypersensitivity can lead to chronic inflammation if the antigen persists, resulting in tissue damage and conditions like sarcoidosis or chronic granulomatous disease.
5. In contrast to other hypersensitivity types, Type IV does not involve antibodies; instead, it relies on cellular immune responses.

Review Questions

• How does Type IV hypersensitivity differ from other types of hypersensitivity reactions?
  • Type IV hypersensitivity differs from other types primarily because it is mediated by T cells rather than antibodies. This leads to a delayed response where symptoms develop 24 to 48 hours post-exposure. In contrast, other hypersensitivities, like Type I (allergic) reactions, involve immediate antibody-mediated responses. Understanding these differences is crucial for recognizing the various mechanisms behind immune responses.
• What role do T cells play in the mechanism of Type IV hypersensitivity, and how does this impact the body's response to antigens?
  • T cells are central to the mechanism of Type IV hypersensitivity. When exposed to specific antigens, naive CD4+ T helper cells differentiate into Th1 cells that produce cytokines, which activate macrophages and cytotoxic CD8+ T cells. This process amplifies inflammation and leads to tissue damage at the site of exposure. The involvement of T cells highlights how this type of hypersensitivity primarily engages cellular immunity rather than humoral immunity.
• Evaluate the implications of Type IV hypersensitivity in relation to chronic inflammatory diseases and how it can affect overall health.
  • Type IV hypersensitivity has significant implications for chronic inflammatory diseases because persistent antigen exposure can lead to sustained immune activation and tissue damage. Conditions such as sarcoidosis and chronic granulomatous disease exemplify how this immune response can contribute to ongoing inflammation and organ dysfunction. Understanding these connections helps in developing therapeutic strategies aimed at regulating the immune response and mitigating associated health issues.

Related terms

T cells: A type of white blood cell that plays a central role in cell-mediated immunity, including the activation of other immune cells and the direct killing of infected or cancerous cells.

Antigens: Substances that trigger an immune response, which can be proteins from pathogens, allergens, or self-antigens in the case of autoimmune reactions.

Granuloma: A structured aggregate of immune cells that forms at sites of chronic inflammation, often as a result of Type IV hypersensitivity to persistent antigens.