Chapter 21 - Section 21.6 - Study Guide - Assess Your Learning Outcomes - Page 845: 2

Hypersensitivity refers to exaggerated immune responses that can lead to tissue damage or other adverse effects. There are four types of hypersensitivity reactions, each characterized by different mechanisms and immune responses. Here are the names, characteristics, and examples of disorders associated with each type of hypersensitivity: **Type I Hypersensitivity (Immediate Hypersensitivity):** - **Mechanism:** Involves the activation of IgE antibodies and mast cells. Upon re-exposure to an allergen, mast cells release histamines and other chemicals, leading to rapid and severe symptoms. - **Examples:** - Allergic rhinitis (hay fever) - Asthma - Anaphylaxis (severe and potentially life-threatening allergic reaction) **Type II Hypersensitivity (Cytotoxic Hypersensitivity):** - **Mechanism:** Involves antibodies (IgM or IgG) targeting specific cells or tissues, leading to cell destruction through mechanisms such as complement activation or antibody-dependent cellular cytotoxicity (ADCC). - **Examples:** - Autoimmune hemolytic anemia (antibodies target red blood cells) - Hemolytic disease of the newborn (Rh incompatibility between mother and fetus) - Myasthenia gravis (antibodies target acetylcholine receptors at neuromuscular junctions) **Type III Hypersensitivity (Immune Complex-Mediated Hypersensitivity):** - **Mechanism:** Immune complexes (aggregates of antigens and antibodies) deposit in various tissues, triggering inflammation and complement activation. - **Examples:** - Systemic lupus erythematosus (SLE) - Rheumatoid arthritis - Serum sickness (resulting from the injection of foreign serum, like after certain treatments) **Type IV Hypersensitivity (Delayed-Type Hypersensitivity):** - **Mechanism:** Involves sensitized T cells, particularly CD4+ T cells. Upon re-exposure to an antigen, these T cells release cytokines that lead to inflammation and tissue damage. - **Examples:** - Contact dermatitis (e.g., poison ivy reaction) - Tuberculin skin test (used to diagnose latent tuberculosis) - Delayed rejection of transplanted organs or tissues It's important to note that hypersensitivity reactions can vary in severity and presentation. Some hypersensitivity reactions can be mild and localized, while others can be severe and systemic, potentially leading to life-threatening conditions. Understanding the mechanisms and characteristics of each type of hypersensitivity is crucial for proper diagnosis, management, and treatment of related disorders.

Hypersensitivity refers to exaggerated immune responses that can lead to tissue damage or other adverse effects. There are four types of hypersensitivity reactions, each characterized by different mechanisms and immune responses. Here are the names, characteristics, and examples of disorders associated with each type of hypersensitivity: **Type I Hypersensitivity (Immediate Hypersensitivity):** - **Mechanism:** Involves the activation of IgE antibodies and mast cells. Upon re-exposure to an allergen, mast cells release histamines and other chemicals, leading to rapid and severe symptoms. - **Examples:** - Allergic rhinitis (hay fever) - Asthma - Anaphylaxis (severe and potentially life-threatening allergic reaction) **Type II Hypersensitivity (Cytotoxic Hypersensitivity):** - **Mechanism:** Involves antibodies (IgM or IgG) targeting specific cells or tissues, leading to cell destruction through mechanisms such as complement activation or antibody-dependent cellular cytotoxicity (ADCC). - **Examples:** - Autoimmune hemolytic anemia (antibodies target red blood cells) - Hemolytic disease of the newborn (Rh incompatibility between mother and fetus) - Myasthenia gravis (antibodies target acetylcholine receptors at neuromuscular junctions) **Type III Hypersensitivity (Immune Complex-Mediated Hypersensitivity):** - **Mechanism:** Immune complexes (aggregates of antigens and antibodies) deposit in various tissues, triggering inflammation and complement activation. - **Examples:** - Systemic lupus erythematosus (SLE) - Rheumatoid arthritis - Serum sickness (resulting from the injection of foreign serum, like after certain treatments) **Type IV Hypersensitivity (Delayed-Type Hypersensitivity):** - **Mechanism:** Involves sensitized T cells, particularly CD4+ T cells. Upon re-exposure to an antigen, these T cells release cytokines that lead to inflammation and tissue damage. - **Examples:** - Contact dermatitis (e.g., poison ivy reaction) - Tuberculin skin test (used to diagnose latent tuberculosis) - Delayed rejection of transplanted organs or tissues It's important to note that hypersensitivity reactions can vary in severity and presentation. Some hypersensitivity reactions can be mild and localized, while others can be severe and systemic, potentially leading to life-threatening conditions. Understanding the mechanisms and characteristics of each type of hypersensitivity is crucial for proper diagnosis, management, and treatment of related disorders.