Hypersensitivity Reactions Overview
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Questions and Answers

What characterizes hypersensitivity reactions?

  • They are harmless reactions to common antigens.
  • They occur exclusively in response to environmental antigens.
  • They primarily depend only on T cells for tissue injury.
  • They involve harmful immune responses against foreign antigens. (correct)

    • What can result from a failure of self-tolerance mechanisms?

  • Autoimmunity leading to reactions against self-antigens. (correct)
  • Decreased responsiveness to microbial antigens.
  • Complete eradication of persistent infections.
  • Increased production of IgE antibodies.

    • What is a significant feature of hypersensitivity diseases?

  • They are only triggered by microbial antigens.
  • They are classified based on immune response types and effector mechanisms. (correct)
  • They exclusively involve T cell-mediated responses.
  • They only involve immediate hypersensitivity reactions.

    • In a population, what percentage may be abnormally responsive to environmental substances?

    <p>20% or more</p> Signup and view all the answers

    What is one of the consequences of excessive immune reactions against microbes?

    <p>Microbial infections may become persistent.</p> Signup and view all the answers

    Which type of antibody is primarily associated with allergic diseases in hypersensitive individuals?

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

    Which of the following statements is accurate regarding humoral and cell-mediated immunities in hypersensitivity?

    <p>Both types can coexist and contribute to tissue injury.</p> Signup and view all the answers

    What is the primary distinction between types of hypersensitivity reactions?

    <p>The type of antigen involved in the reaction.</p> Signup and view all the answers

    What characterizes hormone production in patients with Graves’ disease?

    <p>It becomes independent of TSH presence and body requirements.</p> Signup and view all the answers

    What is the main effect of autoantibodies in myasthenia gravis?

    <p>They reduce the number of acetylcholine receptors on muscle cells.</p> Signup and view all the answers

    Which mechanism is NOT involved in the destruction of RBCs in autoimmune hemolytic anemia?

    <p>Endocytosis by phagocytes without receptor binding.</p> Signup and view all the answers

    How do antibodies function as antagonists in the context of cell-surface receptors?

    <p>They block receptor function upon binding.</p> Signup and view all the answers

    What type of antibodies are generally involved in cell- or tissue-specific diseases?

    <p>Autoantibodies produced during autoimmune responses.</p> Signup and view all the answers

    What results from the binding of autoantibodies to acetylcholine receptors in myasthenia gravis?

    <p>Decreased receptor availability on muscle cells.</p> Signup and view all the answers

    In autoimmune hemolytic anemia, which receptor type contributes to RBC destruction through opsonization?

    <p>Fcγ receptors on phagocytes.</p> Signup and view all the answers

    Which statement about the mechanisms of autoreactive antibodies is true?

    <p>Some antibodies can block receptor activity while others can stimulate it.</p> Signup and view all the answers

    What characterizes the immune response in allergic diseases compared to autoimmune diseases?

    <p>It involves type I hypersensitivity reaction mediated by IgE.</p> Signup and view all the answers

    What is the role of autoantibodies that act as receptor antagonists?

    <p>They block the natural ligand from binding to the receptor.</p> Signup and view all the answers

    In which condition do autoantibodies against the TSH receptor lead to excessive thyroid hormone production?

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

    Which type of hypersensitivity reaction is uniquely associated with allergic diseases?

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

    How do autoantibodies against streptococcal antigens contribute to rheumatic fever?

    <p>They cross-react with heart tissue due to structural similarity.</p> Signup and view all the answers

    What is a common mechanism by which autoantibodies mediate disease in autoimmune disorders?

    <p>Binding to and modulating receptor activity</p> Signup and view all the answers

    What effect does the binding of autoantibodies (agonists) to the TSH receptor have in Graves’ disease?

    <p>Continuous stimulation of thyroid hormone release</p> Signup and view all the answers

    What are the main similarities between the mechanisms of allergic reactions and autoimmune diseases?

    <p>Both involve the binding of antibodies to target cells.</p> Signup and view all the answers

    What is the primary mechanism of tissue injury in immune complex-mediated diseases?

    <p>Inflammation caused by complement activation and leukocyte recruitment</p> Signup and view all the answers

    In Goodpasture's syndrome, what is observed in immunofluorescence?

    <p>Smooth (linear) deposits of antibody along the basement membrane</p> Signup and view all the answers

    Which type of immune response is primarily responsible for tissue injury in T cell-mediated diseases?

    <p>Cytokine production by CD4+ T cells</p> Signup and view all the answers

    Which statement about immune complex-mediated diseases is true?

    <p>They can create systemic disorders due to antigen-antibody complexes.</p> Signup and view all the answers

    What type of inflammation is seen in glomerulonephritis associated with systemic lupus erythematosus (SLE)?

    <p>Neutrophilic inflammation with coarse deposits</p> Signup and view all the answers

    How do T lymphocytes typically cause tissue injury?

    <p>By releasing cytokines and directly killing target cells</p> Signup and view all the answers

    What characterizes the inflammation associated with antibody-mediated glomerulonephritis?

    <p>Presence of antibody deposits that are linear</p> Signup and view all the answers

    In the context of immune complex-mediated diseases, what could promote the recruitment of neutrophils?

    <p>Formation of immune complexes in kidneys</p> Signup and view all the answers

    How can humans be sensitized for delayed-type hypersensitivity (DTH) reactions?

    <p>Through microbial infections, contact sensitization, or injection of protein antigens</p> Signup and view all the answers

    What is the primary purpose of the purified protein derivative (PPD) in relation to tuberculosis?

    <p>To diagnose previous or current tuberculosis exposure</p> Signup and view all the answers

    In a positive tuberculin skin test response, what indicates prior exposure to tuberculosis?

    <p>An indurated hypersensitivity reaction</p> Signup and view all the answers

    What autoimmune characteristic is commonly observed in patients with rheumatoid arthritis?

    <p>High levels of IgM, IgG, and IgA antibodies specific for the Fc region of human IgG</p> Signup and view all the answers

    What is a common goal of current treatments for autoimmune diseases?

    <p>To reduce immune activation and its harmful effects</p> Signup and view all the answers

    In terms of hypersensitivity reactions, which type of hypersensitivity is exemplified by the tuberculin reaction?

    <p>Type 4 hypersensitivity</p> Signup and view all the answers

    Which factor does NOT contribute to DTH reactions according to the given information?

    <p>Viral infections</p> Signup and view all the answers

    Which of the following statements about cytokine antagonists is most accurate?

    <p>They have a wide range of applications in immunologic diseases</p> Signup and view all the answers

    Study Notes

    Hypersensitivity Reactions

    • Hypersensitivity refers to harmful immune responses against foreign antigens like environmental substances, drugs, and microbes.
    • In healthy individuals, there is no reaction towards harmless environmental substances, but 20% of the population may be abnormally responsive to one or more of these substances.
    • Hypersensitivity reactions are classified based on the type of immune response, the mechanism responsible for cell and tissue injury, and the effector mechanism.
    • Reactions can be antibody-dependent or T cell-dependent.

    Classification of Hypersensitivity

    • Type I: IgE-mediated, involves allergic reaction involving mast cells and basophils.
    • Type II: Antibody-dependent cytotoxic reactions, involves antibodies binding to cell surface antigens.
    • Type III: Immune complex-mediated reactions, involves the formation of immune complexes that deposit in tissues and activate complement.
    • Type IV: Cell-mediated reactions, involves T cell-mediated responses.

    Autoimmunity

    • Occurs when immune system reacts against self-antigens, causing autoimmune diseases.
    • Breakdown in self-tolerance mechanisms leads to T and B cell mediated responses.
    • Examples: rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis.

    Antibody-Mediated Diseases

    • Antibodies act as either agonists or antagonists.
    • Agonists mimic the natural ligand and activate the receptor.
    • Antagonists block the natural ligand and inhibit receptor activation.

    Examples of Antibody-Mediated Diseases

    • Graves' disease: AutoAbs against TSH receptor, cause overproduction of thyroid hormones.
    • Myasthenia gravis: AutoAbs against acetylcholine receptor, decrease muscle contraction efficiency.
    • Autoimmune hemolytic anemia: Antibodies target red blood cells, leading to their destruction.
    • Glomerulonephritis: Antibodies target glomerular basement membrane, causes inflammation and damage.

    Immune Complex-Mediated Diseases

    • Involve immune complexes formed in circulation and deposited in tissues.
    • Immune complexes usually composed of antibodies against self-antigens or foreign antigens.
    • Primarily affect multiple organs, but sometimes they affect the kidneys.
    • Examples: Systemic Lupus Erythematosus (SLE).

    Cell-Mediated Diseases

    • T lymphocytes can cause tissue damage through cytokine production or direct killing of target cells.
    • CD4+ T cells mainly contribute to inflammation, while CD8+ CTLs kill cells.
    • T cells involved can be autoreactive or specific for foreign antigens present in tissues.

    Examples of Cell-Mediated Diseases

    • Contact hypersensitivity: Response to environmental antigens, like poison ivy.
    • Tuberculin reaction: Delayed-type Hypersensitivity (DTH) response to Mycobacterium tuberculosis antigens.

    Treatment of Immunologic Diseases

    • Focus on reducing immune activation and the injurious consequences of the autoimmune response.
    • Therapeutic approaches include cytokine antagonists and monoclonal antibodies.

    Pathogenesis of Autoimmune Diseases

    • Systemic lupus erythematosus (SLE): Involves the production of autoantibodies against various components of the nucleus, resulting in tissue inflammation and damage.
    • Rheumatoid arthritis (RA): Involves the production of autoantibodies against the Fc region of IgG, known as rheumatoid factor.

    Treatment of Rheumatoid Arthritis

    • Current treatment focuses on reducing immune activation and inflammation.
    • TNF-α inhibitors have shown significant success in managing RA symptoms.

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    Lecture 22: Hypersensitivity Disorders - 11/04/2024 PDF

    Description

    This quiz covers the fundamental concepts of hypersensitivity reactions, including their classification and mechanisms. You'll learn about the four types of hypersensitivity reactions and how immune responses can lead to harmful effects. Ideal for students studying immunology or related fields.

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