Type IV hypersensitivity

Definition

Type IV hypersensitivity, also known as delayed-type hypersensitivity, is an immune response that is mediated by T cells rather than antibodies. This form of hypersensitivity usually takes 24 to 72 hours to develop after exposure to an antigen, as it involves the activation and proliferation of T helper 1 cells and cytotoxic T cells. Conditions such as contact dermatitis and graft-versus-host disease are examples of this type of immune reaction, highlighting its role in tissue damage and inflammation.

5 Must Know Facts For Your Next Test

1. Type IV hypersensitivity is distinct from other types because it does not involve antibodies but instead relies on T cell activation.
2. This hypersensitivity reaction is crucial for the body's defense against intracellular pathogens like viruses and some bacteria.
3. The process involves antigen presentation by dendritic cells to naive T cells, leading to their differentiation into effector T cells.
4. Symptoms of Type IV hypersensitivity can manifest in conditions such as poison ivy rash or reactions to certain metals like nickel.
5. Chronic Type IV hypersensitivity can lead to tissue damage and scarring, emphasizing the importance of regulation in immune responses.

Review Questions

• What is the primary mechanism that distinguishes Type IV hypersensitivity from other types of hypersensitivity reactions?
  • The primary mechanism that sets Type IV hypersensitivity apart is its reliance on T cells rather than antibodies. In this type of reaction, T helper 1 cells and cytotoxic T cells are activated in response to specific antigens. This activation leads to a delayed immune response that typically occurs 24 to 72 hours after exposure, contrasting with immediate reactions seen in other types such as Type I hypersensitivity.
• Discuss the role of antigen presenting cells in the development of Type IV hypersensitivity reactions.
  • Antigen presenting cells (APCs), particularly dendritic cells, play a critical role in initiating Type IV hypersensitivity reactions. When APCs capture and process an antigen, they present it on their surface using major histocompatibility complex (MHC) molecules. This presentation activates naive T cells, leading them to differentiate into effector T cells that mediate the immune response. The effectiveness of this process is vital for a proper delayed-type reaction to occur.
• Evaluate the implications of chronic Type IV hypersensitivity on tissue health and the potential for developing autoimmune conditions.
  • Chronic Type IV hypersensitivity can significantly impact tissue health by causing persistent inflammation and cellular damage. Over time, this ongoing immune response can result in scarring and dysfunction of affected tissues. Additionally, if the immune system becomes dysregulated due to repeated exposure to antigens or other factors, it could lead to autoimmune conditions where the body mistakenly attacks its own tissues, showcasing the delicate balance required for maintaining immune homeostasis.

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 direct killing of infected or cancerous cells.

Antigen: Any substance that can trigger an immune response, typically a protein or polysaccharide found on the surface of pathogens, allergens, or foreign tissues.

Contact dermatitis:

A localized skin reaction caused by exposure to irritants or allergens, characterized by redness, itching, and blistering, often resulting from Type IV hypersensitivity.