Hypersensitivity Reactions Overview

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Questions and Answers

Which type of hypersensitivity reaction is characterized by T-cell-mediated inflammation?

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

What is a common feature of Type I hypersensitivity reactions?

  • Immune complexes deposit in tissues.
  • T cells destroy pancreatic beta cells.
  • IgG/IgM antibodies attack self-tissue.
  • Mast cell degranulation occurs. (correct)

Which of the following is NOT a risk factor for Type IV hypersensitivity?

  • Contact with certain chemicals like formaldehyde
  • Infectious diseases like tuberculosis
  • Exposure to allergens like poison ivy
  • Blood transfusions (correct)

For which type of hypersensitivity is prior exposure indicated by a positive Mantoux test?

<p>Type IV hypersensitivity (A)</p> Signup and view all the answers

Which statement about Type II hypersensitivity is correct?

<p>It results from IgG/IgM antibodies attacking self-tissue. (B)</p> Signup and view all the answers

What initiates the production of IgE antibodies in Type I hypersensitivity reactions?

<p>Initial exposure to environmental allergens (C)</p> Signup and view all the answers

Which clinical manifestation is associated with Type I hypersensitivity reactions?

<p>Urticaria (hives) (D)</p> Signup and view all the answers

What is the mechanism of action behind Type II hypersensitivity reactions?

<p>Opsonization and phagocytosis of cells (B)</p> Signup and view all the answers

Which of the following conditions is an example of Type II hypersensitivity?

<p>Myasthenia gravis (B)</p> Signup and view all the answers

In Type I hypersensitivity, which substance is primarily released by mast cells upon re-exposure to an allergen?

<p>Histamine (D)</p> Signup and view all the answers

What are commonly associated risk factors for Type I hypersensitivity reactions?

<p>Family history of allergies and environmental exposure (B)</p> Signup and view all the answers

Which of the following best describes Type II hypersensitivity reactions?

<p>Cell destruction mediated by antibodies against specific antigens (D)</p> Signup and view all the answers

What is a key characteristic of Type I hypersensitivity reactions regarding their transmissibility?

<p>They are not transmissible (A)</p> Signup and view all the answers

What is the primary cause of Type III Hypersensitivity?

<p>The formation of immune complexes that are deposited in tissues (D)</p> Signup and view all the answers

What occurs during the sensitization phase of Type IV Hypersensitivity?

<p>Memory T cells are generated (A)</p> Signup and view all the answers

Which statement accurately describes the pathophysiology of Type III Hypersensitivity?

<p>Immune complexes activate the Complement System, leading to tissue damage. (C)</p> Signup and view all the answers

What type of agents can trigger Type IV Hypersensitivity?

<p>Environmental antigens like poison ivy (C)</p> Signup and view all the answers

Which of the following autoimmune diseases is categorized under Type III Hypersensitivity?

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

In Type IV Hypersensitivity, which cells are primarily involved in the delayed inflammatory response?

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

What kind of response is characterized by the recruitment of neutrophils in Type III Hypersensitivity?

<p>Complement activation response (B)</p> Signup and view all the answers

Flashcards

Type I hypersensitivity

An immune response triggered by exposure to allergens, involving IgE antibodies binding to mast cells and leading to the release of histamine, leukotrienes, and prostaglandins.

Sensitization Phase

The initial exposure to an allergen that leads to the production of IgE antibodies which bind to mast cells and basophils.

Re-exposure Phase

Re-exposure to the same allergen, triggering cross-linking of IgE on the surface of mast cells, leading to their degranulation and the release of inflammatory mediators.

Clinical Manifestations of Type I Hypersensitivity

A set of reactions that include hives (urticaria), allergic rhinitis (hay fever), asthma, and in severe cases, anaphylaxis.

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Type II hypersensitivity

An immune response directed against antigens present on cell surfaces involving IgG or IgM antibodies.

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Antibody-Mediated Destruction

The process where IgG or IgM antibodies bind to antigens on cell surfaces leading to their destruction by macrophages or the complement system.

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Graves' disease

A disorder where antibodies bind to TSH receptors, leading to overstimulation of the thyroid, causing hyperthyroidism.

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Myasthenia gravis

A disorder where antibodies block acetylcholine receptors at the neuromuscular junction, resulting in muscle weakness and fatigue.

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Autoimmune Disease

Immune system attacks the body's own tissues, causing inflammation and damage.

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Risk Factor for Autoimmune Disease

Genetic predisposition, family history of autoimmune diseases and autoimmune disorders like Graves' disease and Myasthenia gravis.

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Immune Complexes

Formation of immune complexes in the tissues, triggering inflammation. This can be seen in conditions like SLE and RA.

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Cytokine Release in Type IV Hypersensitivity

The release of inflammatory chemicals like IFN-γ and TNF-α by T cells, attracting macrophages to the site of infection and further causing inflammation.

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What is Type 1 diabetes?

An immune response where T cells attack and destroy pancreatic beta cells, which are responsible for producing insulin. This leads to a deficiency in insulin and the development of diabetes.

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What does a positive TB skin test mean?

A positive Mantoux test indicates that a person has been exposed to Mycobacterium tuberculosis. However, it does not mean they have active TB.

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What is Type IV hypersensitivity?

Type IV hypersensitivity is delayed, involving T cells. The body's immune system reacts to allergens like poison ivy, causing inflammation and redness.

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What is Type II hypersensitivity?

Type II hypersensitivity involves antibodies that target self-tissues, leading to their destruction. This can occur in diseases like myasthenia gravis and Graves' disease.

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How can tuberculosis trigger Type IV hypersensitivity?

Type IV hypersensitivity can be triggered by infectious diseases like tuberculosis, leading to a strong immune response.

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Study Notes

Hypersensitivity Reactions

  • Hypersensitivity reactions are immune responses that cause harm rather than benefit.
  • Four main types of hypersensitivity reactions exist: Type I, Type II, Type III, and Type IV.

Type I Hypersensitivity (Immediate/Allergic Reactions)

  • Cause: Exposure to allergens like pollen, pet dander, food, insect venom, or medications.
  • Pathophysiology:
    • Sensitization phase: Initial exposure triggers IgE antibody production, binding to mast cells and basophils.
    • Re-exposure: Subsequent exposure causes cross-linking of IgE, triggering mast cell degranulation and release of histamine, leukotrienes, prostaglandins.
    • This leads to increased vascular permeability, smooth muscle contraction, and mucus secretion.
  • Clinical Manifestations: Urticaria (hives), allergic rhinitis (hay fever), asthma, and anaphylaxis.
  • Transmission: Not transmissible; a response triggered by exposure to allergens.
  • Risk Factors: Genetic predisposition to atopy (family history of allergies, asthma, or eczema), environmental exposure to allergens, and occupation-related exposure.

Type II Hypersensitivity (Cytotoxic Reactions)

  • Cause: Autoimmune disorders (e.g., Graves' disease, Myasthenia gravis) and blood transfusion reactions where the body's immune system targets its own tissues (self-antigens) or foreign antigens.
  • Pathophysiology:
    • Antibodies (IgG or IgM) bind to antigens on cell surfaces.
    • This leads to opsonization and phagocytosis by macrophages.
    • Complement system activation causes cell lysis and death.
  • Examples: Graves' disease (antibodies bind to TSH receptors), Myasthenia gravis (antibodies block acetylcholine receptors).
  • Transmission: Not transmissible; a result of the body's immune response to self or foreign antigens.

Type III Hypersensitivity (Immune Complex-Mediated)

  • Cause: Formation of immune complexes (antigen-antibody complexes) that deposit in tissues, leading to inflammation.
  • Pathophysiology:
    • Circulating immune complexes become trapped in blood vessels or tissues.
    • Complement activation recruits neutrophils, releasing enzymes causing tissue damage.
    • Inflammation and necrosis result in organ damage.
  • Examples: Systemic lupus erythematosus (SLE), rheumatoid arthritis (RA).
  • Transmission: Not transmissible; a result of the body's immune response to self or foreign antigens.
  • Risk Factors: Autoimmune diseases (e.g., SLE and RA), chronic infections.

Type IV Hypersensitivity (Delayed/Cell-Mediated)

  • Cause: Exposure to environmental antigens (e.g., poison ivy), medications, or infectious agents.
  • Pathophysiology:
    • Sensitization phase: Memory T cells are generated after initial exposure.
    • Re-exposure: Activates memory T cells, releasing cytokines like IFN-γ and TNF-α.
    • Delayed inflammatory response leads to macrophage recruitment and tissue damage.
  • Examples: Contact dermatitis (e.g., poison ivy).
  • Transmission: Not transmissible; a result of T-cell-mediated immune responses.
  • Risk Factors: Exposure to allergens, topical medications, chemicals like formaldehyde, and infections (e.g., Tuberculosis).

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