Hypersensitivity

Definition

Hypersensitivity refers to an exaggerated or inappropriate immune response to a foreign substance, leading to tissue damage and other adverse effects. This response can occur upon re-exposure to an allergen, where the immune system reacts excessively, causing symptoms that can range from mild to severe. There are different types of hypersensitivity reactions classified based on their underlying mechanisms, which connect closely with both innate and adaptive immune responses.

5 Must Know Facts For Your Next Test

1. Hypersensitivity reactions can be classified into four types: Type I (immediate), Type II (cytotoxic), Type III (immune complex-mediated), and Type IV (delayed-type).
2. Type I hypersensitivity is mediated by IgE antibodies and is commonly associated with allergies such as hay fever, asthma, and food allergies.
3. Type II hypersensitivity involves IgG or IgM antibodies that target specific cells, leading to cell destruction, often seen in conditions like hemolytic anemia.
4. Type III hypersensitivity results from the formation of immune complexes that deposit in tissues, leading to inflammation and damage, seen in diseases like systemic lupus erythematosus.
5. Type IV hypersensitivity is T-cell mediated and does not involve antibodies; it can result in delayed reactions such as contact dermatitis from poison ivy exposure.

Review Questions

• What are the different types of hypersensitivity reactions and how do they differ in their mechanisms?
  • There are four main types of hypersensitivity reactions. Type I is an immediate reaction mediated by IgE antibodies and is associated with allergens, leading to symptoms like asthma or hay fever. Type II involves IgG or IgM antibodies that cause cytotoxic effects on specific cells. Type III is characterized by immune complexes that deposit in tissues, causing inflammation. Finally, Type IV is a delayed-type reaction mediated by T-cells and does not involve antibodies, typically resulting in contact dermatitis.
• Discuss the role of immunoglobulin E (IgE) in allergic reactions related to hypersensitivity.
  • Immunoglobulin E (IgE) plays a critical role in Type I hypersensitivity reactions. When an individual is exposed to an allergen for the first time, IgE antibodies are produced. Upon subsequent exposures to the same allergen, these IgE antibodies bind to mast cells and basophils, leading to their degranulation and the release of histamine and other inflammatory mediators. This cascade effect results in the symptoms commonly associated with allergic reactions such as itching, swelling, and difficulty breathing.
• Evaluate the impact of hypersensitivity reactions on overall health and quality of life for affected individuals.
  • Hypersensitivity reactions can significantly impact overall health and quality of life for individuals experiencing them. For those with severe allergies or conditions like anaphylaxis, exposure to common allergens can lead to life-threatening situations requiring immediate medical intervention. Chronic allergic conditions such as asthma can limit physical activity and lead to ongoing health issues. Additionally, the psychological toll from managing these conditions can cause anxiety and social limitations. Therefore, understanding and managing hypersensitivity is crucial for improving health outcomes for affected individuals.

Related terms

Allergen: A substance that triggers an allergic reaction, causing the immune system to respond inappropriately.

Anaphylaxis: A severe, life-threatening allergic reaction characterized by rapid onset of symptoms such as difficulty breathing, swelling, and shock.

Immunoglobulin E (IgE): A class of antibody associated with allergic reactions and hypersensitivity; it binds to allergens and triggers the release of histamine from mast cells.