Hypersensitivity Reactions Overview
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Hypersensitivity Reactions Overview

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Questions and Answers

What type of hypersensitivity reaction is characterized by an immediate response after antigen interaction with IgE antibodies?

  • Type IV hypersensitivity
  • Type I hypersensitivity (correct)
  • Type II hypersensitivity
  • Type III hypersensitivity

    • Which antibody is primarily involved in Type I hypersensitivity reactions?

  • IgE (correct)
  • IgG
  • IgA
  • IgM

    • What is a necessary condition for an individual to develop a Type I hypersensitivity reaction?

  • Exposure to high doses of the allergen
  • Genetic mutation affecting IgE production
  • A previous sensitization to the allergen (correct)
  • Infection with a specific pathogen

    • Which of the following is NOT an example of a common allergen that triggers Type I hypersensitivity reactions?

    <p>Self antigens</p> Signup and view all the answers

    What percentage of the population is estimated to be affected by Type I hypersensitivity reactions?

    <p>10-20%</p> Signup and view all the answers

    Which term describes the genetic predisposition associated with hypersensitivity reactions?

    <p>Genetic susceptibility</p> Signup and view all the answers

    Which type of hypersensitivity reaction is associated with immune complex-mediated disorders?

    <p>Type III hypersensitivity</p> Signup and view all the answers

    Which of the following is considered a Type IV hypersensitivity reaction?

    <p>Contact dermatitis</p> Signup and view all the answers

    Hypersensitivity reactions can be classified into how many main types?

    <p>Four</p> Signup and view all the answers

    What is the primary consequence of antibodies formed against TSH receptors in Hashimoto thyroiditis?

    <p>Blockage of TSH action leading to hypothyroidism</p> Signup and view all the answers

    Which of the following diseases is characterized by antibodies acting like TSH?

    <p>Grave’s disease</p> Signup and view all the answers

    Which of the following is NOT an example of a type II hypersensitivity reaction?

    <p>Rheumatoid arthritis</p> Signup and view all the answers

    In autoimmune hemolytic anemia, which component of blood is primarily affected?

    <p>Red blood cells</p> Signup and view all the answers

    What type of antibodies are involved in the hyperacute rejection reaction?

    <p>Antibodies against donor antigen</p> Signup and view all the answers

    Islet cell autoantibodies are indicative of which autoimmune condition?

    <p>Type 1 diabetes mellitus</p> Signup and view all the answers

    What is the primary role of TH2 cells during initial exposure to an antigen?

    <p>To secrete cytokines that stimulate various immune responses.</p> Signup and view all the answers

    What is the effect of IL-4 in the sensitization process?

    <p>Stimulates B cells to produce IgE antibodies.</p> Signup and view all the answers

    Which mediators are primarily responsible for the immediate phase response in type I hypersensitivity?

    <p>Preformed mediators such as histamine and proteases.</p> Signup and view all the answers

    What characterizes the late-phase reaction after allergen re-exposure?

    <p>Infiltration of tissues with eosinophils and neutrophils.</p> Signup and view all the answers

    In type II hypersensitivity, what is the primary mechanism of cell damage during a complement-dependent reaction?

    <p>Lysis of cells due to complement activation.</p> Signup and view all the answers

    What is one characteristic feature of an anaphylactic reaction?

    <p>Severe hypotension and widespread urticaria.</p> Signup and view all the answers

    Which type of antibody is primarily involved in type II hypersensitivity reactions?

    <p>IgG</p> Signup and view all the answers

    How do antibodies mediate cellular dysfunction in type II hypersensitivity?

    <p>By altering the signaling pathways of target cells.</p> Signup and view all the answers

    What role do mast cells play in the type I hypersensitivity response?

    <p>They release mediators that cause allergy symptoms upon re-exposure to an allergen.</p> Signup and view all the answers

    What is a common example of localized type I hypersensitivity?

    <p>Hay fever triggered by pollen exposure.</p> Signup and view all the answers

    Study Notes

    Hypersensitivity Reactions

    • Definition: An exaggerated immune response to an antigen, resulting in tissue damage, disease, or even death.
    • Characteristics:
      • Priming: Prior exposure to the allergen is necessary for sensitization.
      • Susceptibility: Genetic predisposition plays a crucial role, often linked to specific genes like HLA.
      • Antigen: Virtually any substance that triggers an immune response can be an allergen.
      • Origin: Antigens can be exogenous (external, e.g., pollen, food) or endogenous (internal, self-antigens).

    Classification of Hypersensitivity Reactions

    • Type I (Immediate):
      • Also known as: Allergic or atopic disorders.
      • Mechanism: Mediated by IgE antibodies bound to mast cells, leading to rapid reactions.
      • Characteristics:
        • Affects approximately 10-20% of the population.
        • Reactions occur within minutes (5-10 minutes) after exposure.
        • Elevated levels of IgE are found in individuals with atopic tendencies.
        • Genetic predisposition is required, and the reaction is triggered by allergens.
        • Examples: Bronchial asthma, hay fever, food allergies.

    Type I Hypersensitivity Reaction Mechanisms

    • Initial Exposure (Sensitization):
      • Presentation: Antigen-presenting cells (APCs, like macrophages) present allergens to T cells.
      • TH2 Activation: T cells differentiate into TH2 cells, secreting cytokines such as IL-4, IL-5, and IL-13.
      • IgE Production: IL-4 stimulates B cells to produce IgE antibodies.
      • Mast Cell Sensitization: IgE binds to Fc receptors on mast cells (located near blood vessels and nerves) and basophils.
      • Note: No reaction occurs during the first exposure; sensitization takes time to develop.
    • Re-exposure to Antigen:
      • Cross-linking: The allergen binds to IgE on mast cells and basophils, causing their activation and degranulation.
      • Mediator Release: Mast cells and basophils release preformed mediators (e.g., histamine, proteases, chemotactic factors), leading to immediate responses.
    • Phases of IgE-Triggered Reactions:
      • Immediate Phase: Occurs within 5-30 minutes and subsides within 60 minutes, characterized by vasodilation, increased vascular permeability, smooth muscle spasm, and glandular secretions.
      • Late-Phase Reaction: Develops 2-8 hours after exposure and can last for days; characterized by tissue infiltration with various immune cells (eosinophils, neutrophils, basophils, monocytes, and TH2 cells) and mucosal epithelial cell damage.

    Examples of Type I Hypersensitivity Reactions

    • Localized Type I:
      • Hay fever: Inflammation of the nasal and conjunctival mucosae, with sneezing and hypersecretion triggered by allergens like pollen.
      • Extrinsic asthma: Wheezing and acute respiratory distress due to bronchospasm and increased mucus secretion caused by allergens such as house dust or animal dander.
    • Systemic Type I (Anaphylaxis):
      • Anaphylactic shock: Hypotension, widespread urticaria, and dyspnea, potentially fatal, often triggered by injected medications (e.g., penicillin) in sensitive individuals.

    Antibody-Mediated (Type II) Hypersensitivity Reactions

    • Definition: Antibodies bind to target cell surface antigens, causing cell lysis.
    • Characteristics:
      • Antibodies: Primarily IgG (occasionally IgM).
      • Antigen: Can be endogenous (self-antigens) or exogenous (adsorbed on cell surfaces or altered by drug metabolites).
      • Mechanisms of Injury:
        • Complement Dependent: C3b and IgG or IgM activate complement, resulting in cell lysis (opsonization & phagocytosis).
        • Antibody-Dependent Cellular Cytotoxicity (ADCC): Antibodies link natural killer cells or macrophages to target cells without phagocytosis or complement activation, leading to cell killing.
        • Antibody-Mediated Cellular Dysfunction: Antibodies bind to cell surface receptors, disrupting function without causing cell injury or inflammation.

    Examples of Type II Hypersensitivity Reactions

    • Antibodies to Blood Cells:
      • Autoimmune hemolytic anemia
      • Transfusion reactions
      • Hemolytic disease of the newborn (erythroblastosis fetalis)
      • Idiopathic thrombocytopenic purpura (ITP)
      • Drug-induced cytotoxic antibodies
    • Antibodies to Tissue Components:
      • Graves’ disease (hyperthyroidism)
      • Myasthenia gravis
      • Type 1 diabetes mellitus (islet cell autoantibodies)
      • Hyperacute rejection reaction (antibodies against donor antigens)

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    Description

    Explore the various hypersensitivity reactions and their characteristics. Understand the mechanisms behind Type I hypersensitivity, including the role of IgE antibodies and the impact on affected individuals. This quiz will test your knowledge on the definitions and classifications of these immune responses.

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