Foundations of Hypersensitivity Reactions
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Questions and Answers

What is an example of a Type IV hypersensitivity reaction?

  • Contact dermatitis (correct)
  • Asthma
  • Anaphylaxis
  • Rheumatoid arthritis

    • What type of cells are involved in the cytolytic T cell response to poison ivy?

    CD8 T cells

    Which of the following diseases can involve Type IV hypersensitivity?

  • Multiple Sclerosis (correct)
  • Type 1 Diabetes Mellitus (correct)
  • Hemophilia
  • Tuberculosis (correct)

    • All diseases only involve one type of hypersensitivity reaction.

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

    What is characterized by mononuclear cell infiltration of the dermis?

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

    What is meant by the term 'immunopathology'?

    <p>The process by which the host's cells/tissues are injured through the host's immunologic reaction to a stimulus.</p> Signup and view all the answers

    Which of the following describes hypersensitivity?

    <p>An injurious adaptive immune reaction</p> Signup and view all the answers

    How many types of hypersensitivity reactions are there?

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

    What type of hypersensitivity reaction is mediated by IgE?

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

    Name one hallmark of the late-phase reaction in Type I hypersensitivity.

    <p>Influx of eosinophils</p> Signup and view all the answers

    In Type II hypersensitivity, antibodies are produced against ______ antigens.

    <p>cellular self</p> Signup and view all the answers

    What is a classic example of a Type III hypersensitivity disease?

    <p>Systemic lupus erythematosus</p> Signup and view all the answers

    Which type of hypersensitivity reaction is mediated primarily by T cells?

    <p>Type IV</p> Signup and view all the answers

    What type of cells are the effector cells in Type IV hypersensitivity reactions?

    <p>T cells</p> Signup and view all the answers

    What is a granuloma reaction?

    <p>A prolonged immune response that walls off an antigen that cannot be cleared.</p> Signup and view all the answers

    What role do mast cells play in Type I hypersensitivity?

    <p>They secrete histamine and other mediators</p> Signup and view all the answers

    Anaphylaxis is an example of a ______ reaction.

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

    Which type of antibody is primarily involved in mediating Type I hypersensitivity reactions?

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

    What distinguishes Type II hypersensitivity from Type III hypersensitivity reactions?

    <p>Type II reactions result in cell damage, Type III primarily causes inflammation.</p> Signup and view all the answers

    Which disease is commonly associated with Type III hypersensitivity reactions?

    <p>Systemic lupus erythematosus</p> Signup and view all the answers

    In the context of immunopathology, which statement about mast cells in Type I hypersensitivity is accurate?

    <p>Mast cells can release multiple inflammatory mediators upon activation.</p> Signup and view all the answers

    What is a key component in the pathogenesis of autoimmune diseases related to hypersensitivity reactions?

    <p>The development of autoreactive T cells.</p> Signup and view all the answers

    What is a critical effect of chronic exposure to allergens on the airways?

    <p>Remodeling leading to airway obstruction</p> Signup and view all the answers

    Which statement accurately describes the mechanism of Type II hypersensitivity?

    <p>Antibodies bind to self-antigens, leading to cell lysis.</p> Signup and view all the answers

    What is the primary function of vasoactive amines released from mast cell granules during an acute inflammatory response?

    <p>Promote vasodilation and vascular leakage</p> Signup and view all the answers

    What triggers the systemic reaction of anaphylaxis?

    <p>A sudden and minimal exposure to an antigen</p> Signup and view all the answers

    Which of the following mediators is associated with the late-phase reaction in Type I hypersensitivity?

    <p>Cytokines such as TNF and IL-4</p> Signup and view all the answers

    What characterizes the sensitization phase in Type II hypersensitivity?

    <p>Development of antibodies against self-antigens</p> Signup and view all the answers

    What genetic predisposition increases the likelihood of IgE production in certain individuals?

    <p>Increased production of T Helper-2 cytokines</p> Signup and view all the answers

    Which of the following diseases exemplifies Type II hypersensitivity?

    <p>Autoimmune hemolytic anemia</p> Signup and view all the answers

    Which of the following conditions is NOT typically associated with Type I hypersensitivity reactions?

    <p>Celiac disease</p> Signup and view all the answers

    What characterizes the initial response during the acute inflammatory reaction mediated by mast cell degranulation?

    <p>Vasoactive amines inducing rapid changes in vascular permeability</p> Signup and view all the answers

    What is the potential outcome of the systemic reaction of anaphylaxis if not treated promptly?

    <p>Progressive vascular shock and potential death</p> Signup and view all the answers

    Which statement best describes why certain antigens preferentially induce an IgE response?

    <p>Genetic factors influence IgE production and low antigen doses favor it.</p> Signup and view all the answers

    What role do phagocytes play in Type II hypersensitivity reactions?

    <p>They ingest antibody-coated cells to clear them.</p> Signup and view all the answers

    Which statement best defines anaphylaxis?

    <p>A severe and rapid systemic allergic reaction.</p> Signup and view all the answers

    In the context of asthma as a Type I hypersensitivity reaction, what is the primary physiological change during a flare-up?

    <p>Constriction of bronchioles due to smooth muscle contraction</p> Signup and view all the answers

    What role do proteases released from secretory granules of mast cells play during an acute inflammatory response?

    <p>Degrading the extracellular matrix and activating complement</p> Signup and view all the answers

    In autoimmune hemolytic anemia, what immunological process leads to red blood cell destruction?

    <p>IgM or IgG antibodies binding to self-antigens</p> Signup and view all the answers

    How does mucus overproduction affect airflow in chronic airway exposure?

    <p>It contributes to airflow obstruction.</p> Signup and view all the answers

    Which characteristic identifies the sensitization phase in Type I hypersensitivity?

    <p>B cells become IgE-secreting plasma cells</p> Signup and view all the answers

    What is the primary effector mechanism involved in Type IV hypersensitivity reactions?

    <p>Activation of T cells and cytokine release</p> Signup and view all the answers

    How does IgE contribute to immediate hypersensitivity reactions?

    <p>By binding to high-affinity receptors on mast cells</p> Signup and view all the answers

    What distinguishes Type II from Type III hypersensitivity reactions?

    <p>Type II has direct cellular damage from antibodies, while Type III involves immune complex formation</p> Signup and view all the answers

    What is a potential consequence of excessive IgE production in sensitized individuals?

    <p>Exaggerated allergic reactions</p> Signup and view all the answers

    Which factor has contributed to the surge in allergy incidence in developed nations?

    <p>Changes in environmental and dietary factors</p> Signup and view all the answers

    What primary characteristic differentiates Type I, II, and III hypersensitivity from Type IV hypersensitivity?

    <p>Type IV is slower and mediated by T cells rather than antibodies</p> Signup and view all the answers

    Which statement best describes the role of mast cells in Type I hypersensitivity?

    <p>Mast cells release granules and cytokines upon cross-linking of IgE</p> Signup and view all the answers

    What is the main immune mechanism involved in the pathology of autoimmune diseases related to hypersensitivity?

    <p>Dysregulation of T cell activation leading to self-tissue targeting</p> Signup and view all the answers

    In what way do cytokines released by mast cells affect the body during a Type I hypersensitivity reaction?

    <p>They promote vasodilation and increase vascular permeability</p> Signup and view all the answers

    Study Notes

    Hypersensitivity Reactions Overview

    • Hypersensitivity reactions are damaging immune responses against foreign or self-antigens.
    • Four types of hypersensitivity reactions exist, classified by immunologic mechanisms (Type I-IV).
    • Immunopathology refers to tissue injury resulting from immune reactions, which can be excessive or misdirected.

    Types of Hypersensitivity

    • Type I (IgE-Mediated)

      • Also known as immediate hypersensitivity; symptoms arise within minutes.
      • Involves B cells producing IgE that binds to mast cells, leading to degranulation upon re-exposure to the antigen.
      • Mediators include vasoactive amines (histamine), lipid mediators (arachidonic acid), and cytokines (TNF, IL-4).
      • Examples: seasonal allergies, urticaria, asthma, anaphylaxis, characterized by vascular shock and airway obstruction.

    • Type II (Antibody-Mediated Cytotoxicity)

      • Involves IgM or IgG antibodies against self-antigens, leading to cell lysis or opsonization for phagocytosis.
      • Can alter normal cell function (e.g., myasthenia gravis, Grave’s disease).
      • Example: autoimmune hemolytic anemia and Goodpasture’s syndrome, where antibody binding results in tissue damage.

    • Type III (Immune-Complex)

      • Formed when antibodies combine with soluble antigens, leading to deposition in blood vessel walls and inflammatory response.
      • Activation of complement recruits neutrophils, which release enzymes causing tissue damage.
      • Examples: systemic lupus erythematosus, post-streptococcal glomerulonephritis, with kidney damage resulting from immune complex deposition.

    • Type IV (T Cell-Mediated)

      • Delayed-type hypersensitivity mediated by T cells, exhibiting a slower response (1-3 days).
      • Cytokines from TH1 cells recruit macrophages, leading to tissue damage.
      • Granuloma formation occurs when antigens persist, limiting spread through walled-off immune responses.
      • Examples: contact dermatitis, granulomatous inflammation from tuberculosis, transplant rejection, and some autoimmune disorders like Type 1 Diabetes and Multiple Sclerosis.

    Key Mechanisms and Terms

    • Sensitization Phase: Initial exposure to an antigen is crucial, as it primes the immune system for subsequent reactions.
    • Bi-Phasic Reaction (Type I): Initial acute response followed by a more sustained late-phase response characterized by eosinophil influx.
    • Granuloma Reaction: Results from prolonged immune activation, often due to chronic infections or allergens.
    • Atopic Individuals: Predisposed to produce IgE due to genetic factors, increasing sensitivity to allergens.

    Clinical Context

    • Hypersensitivity reactions can lead to various diseases encountered across multiple clinical contexts.
    • Increased allergy incidence in developed nations, particularly among children.
    • Understanding these mechanisms is vital for diagnosing and managing allergic diseases and autoimmune conditions.

    Acute Inflammatory Response

    • Characteristic symptoms arise from mast cell mediators initiating an acute inflammatory response.
    • Initial response (1-2 hours) involves:
      • Vasodilating vasoactive amines (notably histamine) released from mast cell granules.
      • Lipid mediators derived from arachidonic acid that promote vascular changes and recruit leukocytes.
      • Proteases in granules that degrade extracellular matrix and activate complement.
    • Late-phase reaction is typically more pronounced and prolonged, marked by cytokines (e.g., TNF and IL-4) orchestrating the immune response, with eosinophil influx being a distinctive feature.

    IgE Production and Allergy

    • Only a subset of antigens trigger an IgE response; lower antigen doses favor production.
    • Genetics influence IgE production; individuals predisposed to increased T Helper-2 cytokines (like IL-4 and IL-13) are termed atopic.

    Hypersensitivity Reactions Overview

    • Hypersensitivity refers to exaggerated immune responses to otherwise harmless substances.
    • Allergy incidents have surged in developed nations, notably among children.
    • Four types of hypersensitivity reactions classified by immunological mechanisms:
      • Types I-III involve direct antibody action.
      • Type IV is mediated by T cells.

    Type I Hypersensitivity (IgE-Mediated)

    • Symptoms manifest rapidly (within minutes of antigen exposure).
    • Sensitization phase begins with initial antigen exposure leading B cells to produce IgE.
    • Secreted IgE binds to high-affinity IgE receptors on mast cells, persisting even in the absence of antigen.
    • Upon subsequent antigen exposure, cross-linking of IgE on mast cells results in granule exocytosis and cytokine release, the effector phase.
    • Chronic exposure may result in airway remodeling: smooth muscle hypertrophy, thickened basement membrane, and increased mucus production.

    Systemic Reactions and Anaphylaxis

    • Anaphylaxis entails severe systemic reactions: vascular shock, widespread edema, and respiratory distress due to bronchiole constriction.
    • Life-threatening reactions can occur with minimal antigen exposure.

    Type II Hypersensitivity (Antibody-Mediated)

    • Mechanism involves sensitization whereby antibodies (primarily IgM or IgG) target cellular (self) antigens.
    • The antibodies bind to cells or extracellular proteins, leading to complement fixation, cell lysis, or opsonization for phagocytic uptake.
    • Examples include autoimmune hemolytic anemia and transfusion reactions.
    • Damage can also arise through inflammation without phagocytosis, involving neutrophil activation and local complement activation.

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    Related Documents

    Hypersensitivity Reactions 2024 PDF
    2024 Hypersensitivity Reactions Lecture Notes PDF

    Description

    This quiz covers the fundamental concepts of hypersensitivity reactions as explored in the Foundations block. Instructors Lonnie Lybarger, PhD, and Erika Bracamonte, MD, guide learners through the mechanisms and classifications of these immune responses. Prepare for both theoretical and clinical aspects discussed during the session.

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