Hypersensitivity Reactions Overview
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Questions and Answers

Which of the following could trigger an autoimmune response?

  • The body's own cells (correct)
  • Eating peanuts
  • A bee sting
  • Exposure to a bacterial infection

    • Which of these is NOT a type of antigen that can cause an infection?

  • Bacteria
  • Dust (correct)
  • Viruses
  • Fungi

    • What type of antigen is usually found in the pollen of plants?

  • Harmless (correct)
  • Autoimmune
  • Self
  • Infectious

    • Which of the following is NOT an example of a harmless antigen?

    <p>A virus (B)</p> Signup and view all the answers

    Which category of antigen is most likely to cause an allergic reaction?

    <p>Harmless (C)</p> Signup and view all the answers

    What is the primary characteristic of a hypersensitivity reaction?

    <p>An overactive immune response to foreign or self antigens. (B)</p> Signup and view all the answers

    What is the key difference between the four types of hypersensitivity?

    <p>The time frame within which the reaction occurs. (A)</p> Signup and view all the answers

    Which of the following is NOT considered a hypersensitivity reaction?

    <p>Normal immune response to a bacterial infection. (A)</p> Signup and view all the answers

    Which type of hypersensitivity is typically associated with autoimmune diseases?

    <p>Type III (A), Type IV (C), Type II (D)</p> Signup and view all the answers

    What is the main reason why hypersensitivity reactions can be harmful?

    <p>They can lead to inflammation and tissue damage, potentially causing organ failure. (D)</p> Signup and view all the answers

    Flashcards

    Hypersensitivity

    An exaggerated immune response to antigens.

    Types of Hypersensitivity

    There are four distinct types of hypersensitivity reactions.

    Mechanism of Hypersensitivity

    Each type of hypersensitivity has unique immunological mechanisms.

    Link to Autoimmune Diseases

    Hypersensitivity can be linked to autoimmune diseases.

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    Exogenous vs Endogenous Antigens

    Exogenous are external antigens; endogenous are self-antigens.

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    Infection antigens

    Antigens that originate from pathogens like bacteria, viruses, and fungi.

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    Harmless substance antigens

    Antigens from non-threatening sources such as pollen, food, and drugs.

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    Food antigens

    Antigens derived from edible items, like eggs, fruits, and nuts.

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    Self antigens

    Molecules from the body that can trigger an autoimmune response.

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    Autoimmunity

    A condition where the immune system mistakenly attacks self antigens.

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    Study Notes

    Hypersensitivity Reactions

    • Hypersensitivity reactions are exaggerated immune responses to exogenous or endogenous (self) antigens.
    • Antigens can be infectious (bacterial, viral, fungal) or harmless substances (animals, wool, drugs, plant pollens, metals, dust, foods). Self antigens can lead to autoimmunity.
    • Stages of hypersensitivity include sensitization (asymptomatic first contact with an antigen) and effector (symptomatic phase during repeated exposure).

    Types of Hypersensitivity

    • There are four types of hypersensitivity reactions: Type I (allergy/immediate), Type II (cytotoxic), Type III (immune complex), and Type IV (delayed/cell-mediated).
    • Type I hypersensitivity is antibody-mediated, while Type IV is cell-mediated. Types I, II, and III are antibody-mediated.
    • Type I hypersensitivity reactions are immediate, symptoms appearing 15-30 minutes, or delayed up to 6-24 hours. These are also known as allergies or atopic reactions; they are often triggered by external antigens, not self-antigens.
    • Type I reactions include localized reactions (e.g., urticaria, allergic rhinitis, asthma); and systemic reactions (anaphylaxis). Anaphylaxis can be life-threatening.
    • Type II cytotoxic hypersensitivity results in cell destruction, and is triggered by antigens on cells; these antigens can either be exogenous (drugs) or endogenous (part of a cell membrane, leading to disease.)
    • Examples of Type II hypersensitivity include blood transfusion reactions, hemolytic disease of the fetus and newborn, and autoimmune diseases (e.g., myasthenia gravis; drug-induced autoimmune hemolytic anemia).
    • Type III immune complex hypersensitivity involves the formation of immune complexes (antibodies bound to antigens); these complexes deposit in tissues and activate complement, leading to inflammation (e.g., vasculitis).
    • Examples of Type III hypersensitivity include Arthus reaction and serum sickness.
    • Type IV delayed hypersensitivity has a delayed onset (48-72 hours). It involves T cells, macrophages, and cytotoxic T cells, and can result in tissue damage and fibrosis.
    • Examples of Type IV include contact dermatitis, granulomatous formation (e.g., tuberculosis, tuberculin skin test), and some autoimmune diseases (e.g., type 1 diabetes, multiple sclerosis).

    Mechanisms of Hypersensitivity Reactions

    • Type I (Immediate):
      • First exposure (sensitization): Plasma cells produce IgE antibodies; IgE binds to mast cells and basophils.
      • Second exposure: Allergen binds to IgE on mast cells, triggering degranulation and release of histamine, tryptase, and other mediators, leading to allergic symptoms (itching, vasodilation, edema, etc.). Late reaction involves eosinophils.
    • Type II (Cytotoxic):
      • IgM or IgG antibodies bind to cell membranes, leading to complement activation, phagocytosis, NK cell activation, and cell lysis, resulting in cell destruction.
    • Type III (Immune Complex):
      • IgG antibodies bind to circulating antigens, forming immune complexes. Complexes deposit in tissues, activate complement, and cause inflammation.
    • Type IV (Delayed):
      • T helper cells (Th1) are activated by antigens. They release cytokines that activate macrophages and cytotoxic T cells, causing delayed tissue damage and inflammation.

    Clinical Examples

    • Many specific conditions fall under the classification of hypersensitivity reactions; examples mentioned in the notes include asthma, SLE, Arthus reaction, serum sickness, myasthenia gravis, transfusion reaction, hemolytic disease of the fetus, and contact dermatitis.

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    Related Documents

    Hypersensitivity Reactions (Immunology) PDF

    Description

    This quiz explores the various types of hypersensitivity reactions including their mechanisms and stages. Delve into the classifications of Type I to Type IV reactions, as well as their implications in immune responses. Test your knowledge of how the body reacts to different antigens and the concept of autoimmunity.

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