Hypersensitivity

Definition

Hypersensitivity refers to an overactive or exaggerated immune response to a specific antigen or stimulus, leading to harmful or damaging effects on the body. It is a key concept in the context of diseases associated with depressed or overactive immune responses.

5 Must Know Facts For Your Next Test

1. Hypersensitivity reactions are classified into four main types (I-IV) based on the underlying immunological mechanisms involved.
2. Type I hypersensitivity, or immediate hypersensitivity, is the most common and involves the release of histamine and other inflammatory mediators by mast cells and basophils.
3. Type II hypersensitivity, or antibody-mediated hypersensitivity, is caused by the binding of antibodies to cell surface antigens, leading to cell lysis or phagocytosis.
4. Type III hypersensitivity, or immune complex-mediated hypersensitivity, is caused by the deposition of antigen-antibody complexes in tissues, triggering inflammation.
5. Type IV hypersensitivity, or cell-mediated hypersensitivity, involves the activation of T cells that release cytokines and recruit other immune cells to the site of the reaction.

Review Questions

• Describe the general mechanism underlying hypersensitivity reactions and how they differ from a normal immune response.
  • Hypersensitivity reactions occur when the immune system overreacts to a specific antigen or stimulus, leading to harmful or damaging effects on the body. In a normal immune response, the immune system recognizes and responds to foreign or harmful substances in a controlled manner. However, in hypersensitivity, the immune system becomes hyperactive, triggering an exaggerated and potentially harmful response that can cause inflammation, tissue damage, and other adverse effects. The key distinction is that hypersensitivity reactions are disproportionate and can result in significant harm to the individual, unlike a typical, well-regulated immune response.
• Explain the different types of hypersensitivity reactions (I-IV) and how they are classified based on the underlying immunological mechanisms.
  • Hypersensitivity reactions are classified into four main types (I-IV) based on the specific immunological mechanisms involved. Type I, or immediate hypersensitivity, involves the rapid release of histamine and other inflammatory mediators by mast cells and basophils. Type II, or antibody-mediated hypersensitivity, is caused by the binding of antibodies to cell surface antigens, leading to cell lysis or phagocytosis. Type III, or immune complex-mediated hypersensitivity, is caused by the deposition of antigen-antibody complexes in tissues, triggering inflammation. Type IV, or cell-mediated hypersensitivity, involves the activation of T cells that release cytokines and recruit other immune cells to the site of the reaction. Understanding these different types of hypersensitivity and their underlying mechanisms is crucial for identifying and managing various immune-related disorders.
• Discuss the role of hypersensitivity in the development of autoimmune diseases and the potential consequences for the body.
  • Autoimmune diseases are a prime example of how hypersensitivity can lead to harmful consequences for the body. In autoimmunity, the immune system mistakenly recognizes the body's own healthy tissues as foreign and mounts an exaggerated, damaging response against them. This overactive immune response, a form of hypersensitivity, can target various organs and systems, leading to chronic inflammation, tissue damage, and a wide range of debilitating symptoms. The underlying mechanisms of autoimmunity often involve a breakdown in the body's ability to distinguish self from non-self, resulting in the immune system attacking its own cells and structures. Understanding the role of hypersensitivity in autoimmune diseases is crucial for developing effective treatment strategies and managing the long-term impact on patient health and quality of life.

Related terms

Allergy: An allergic reaction is a type of hypersensitivity response where the immune system overreacts to a normally harmless substance, such as pollen or certain foods.

Autoimmunity: Autoimmune diseases are caused by the immune system mistakenly attacking the body's own healthy tissues, a form of hypersensitivity.

Inflammation:

Inflammation is a common feature of hypersensitivity reactions, as the immune system responds to the perceived threat by increasing blood flow and recruiting immune cells to the affected area.