Immunopathology: Hypersensitivity Overview
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What distinguishes the type III hypersensitivity reaction from type I in terms of antibodies?

Type III hypersensitivity involves IgG antibodies, while type I involves IgE antibodies.

What is the typical time frame for reaching the peak of an Arthus reaction?

The Arthus reaction typically peaks at 4-8 hours.

What triggers the condition known as extrinsic allergic alveolitis?

Extrinsic allergic alveolitis is triggered by inhaled antigen complexes with specific IgG in the alveoli.

How does type IV hypersensitivity differ in its initiation compared to types I and III?

<p>Type IV hypersensitivity is initiated by antigen-specific T cells, unlike type I and III which involve antibodies.</p> Signup and view all the answers

What role do cytokines play in the response of type IV hypersensitivity?

<p>Cytokines produced by activated T cells recruit macrophages and other T cells, creating a cellular infiltrate.</p> Signup and view all the answers

What distinguishes hypersensitivity reactions from protective immune reactions?

<p>Hypersensitivity reactions are exaggerated or inappropriate immune responses that cause tissue damage, unlike protective immune reactions that promote healing and defense.</p> Signup and view all the answers

Describe the mediators involved in Type I hypersensitivity reactions.

<p>Type I hypersensitivity reactions are mediated by IgE, which induces the activation of mast cells resulting in the release of histamines and other inflammatory mediators.</p> Signup and view all the answers

What are the mechanisms through which Type II hypersensitivity leads to tissue damage?

<p>Type II hypersensitivity involves IgG binding to cell-surface or matrix antigens, engaging Fc-receptor and complement-mediated effector mechanisms that can damage the cells.</p> Signup and view all the answers

What characterizes Type III hypersensitivity reactions?

<p>Type III hypersensitivity reactions are characterized by the formation of immune complexes of IgG and soluble antigens, leading to tissue damage through Fc-receptor and complement activation.</p> Signup and view all the answers

Explain the role of T cells in Type IV hypersensitivity reactions.

<p>In Type IV hypersensitivity, T cells mediate the immune response; TH1 cells activate macrophages for inflammation, and cytotoxic T cells directly inflict damage on tissues.</p> Signup and view all the answers

How do environmental and genetic factors contribute to hypersensitivity?

<p>Environmental factors like allergens and pollutants, along with genetic predispositions, can increase the risk of developing hypersensitivity by influencing immune system responses.</p> Signup and view all the answers

What therapeutic strategies are used to manage hypersensitivity reactions?

<p>Therapeutic strategies for hypersensitivity reactions include avoidance of triggers, use of antihistamines, corticosteroids, and immunotherapy to desensitize patients.</p> Signup and view all the answers

Identify and briefly explain the three groups of damage caused by Type IV hypersensitivity.

<p>The three groups include damage from TH1 cell activation leading to macrophage inflammation, TH2 cell-induced eosinophil responses, and direct cytotoxic effects from CTLs.</p> Signup and view all the answers

What activates mast cells in allergic responses?

<p>Mast cells are activated by the cross-linking of Fc epsilonRI receptors through antigen binding to bound IgE molecules.</p> Signup and view all the answers

What is eotaxin and its role in allergic asthma?

<p>Eotaxin is a chemokine released by eosinophils, playing a crucial role in recruiting these cells to sites of allergic inflammation in asthma.</p> Signup and view all the answers

How does genetic susceptibility affect the incidence of allergic diseases?

<p>Individuals with allergic parents are more than twice as likely to develop allergies, whereas those with non-allergic parents have less than half the likelihood compared to the general population.</p> Signup and view all the answers

What is the ‘hygiene hypothesis’ regarding allergic diseases?

<p>The 'hygiene hypothesis' suggests that early exposure to infectious agents promotes a TH1 immune response, reducing the risk of developing atopic diseases.</p> Signup and view all the answers

What causes allergic rhinitis, commonly known as hay fever?

<p>Allergic rhinitis is caused by airborne allergens reacting with IgE-sensitized mast cells in the nasal passages and conjunctiva.</p> Signup and view all the answers

What are the life-threatening reactions associated with systemic anaphylaxis?

<p>Systemic anaphylaxis can be triggered by ingestion of nuts or seafood, insect bites, or drug injections, leading to severe vasodilation and bronchoconstriction.</p> Signup and view all the answers

What is the role of environmental factors in developing atopic allergic diseases?

<p>Environmental factors, along with genetic susceptibility, significantly influence the development of atopic allergic diseases, with exposure levels affecting immune responses.</p> Signup and view all the answers

In type I hypersensitivity, what mechanisms lead to symptoms like asthma?

<p>In type I hypersensitivity, symptoms like asthma result from the release of vasoactive mediators leading to bronchoconstriction and inflammation.</p> Signup and view all the answers

What is the reaction time for a contact hypersensitivity reaction?

<p>48-72 hours</p> Signup and view all the answers

What histological features are characteristic of contact eczema?

<p>Lymphocytes and macrophages, along with edema of the epidermis.</p> Signup and view all the answers

In a tuberculin hypersensitivity reaction, which cells are primarily involved?

<p>Lymphocytes, monocytes, and macrophages.</p> Signup and view all the answers

What characterizes a granuloma in delayed hypersensitivity?

<p>Persistent antigen presence, hardening, and the formation of giant cells.</p> Signup and view all the answers

What is the typical timeframe for granuloma formation?

<p>21-28 days</p> Signup and view all the answers

List one example of an antigen that could lead to contact hypersensitivity.

<p>Poison ivy or heavy metals.</p> Signup and view all the answers

What type of immune response is elicited by intracellular microorganisms like mycobacteria?

<p>A cell-mediated immune response.</p> Signup and view all the answers

Describe the role of TH1 cells in delayed hypersensitivity reactions.

<p>TH1 cells influence and regulate the cell-mediated immune response.</p> Signup and view all the answers

What determines the type of IgE-mediated allergic reaction?

<p>The dose and route of allergen exposure.</p> Signup and view all the answers

What are the two main mechanisms by which Type II hypersensitivity leads to cell destruction?

<p>Fc dependent mechanisms and complement recruitment via the classical pathway.</p> Signup and view all the answers

What is the main consequence of immune mediated hemolytic anemia (IMHA)?

<p>The loss of red blood cells due to their destruction.</p> Signup and view all the answers

Describe how hemolysis occurs in autoimmune hemolytic anemia (AIHA).

<p>Hemolysis occurs due to antibodies binding to red blood cells, leading to ADCC or complement-mediated lysis.</p> Signup and view all the answers

What initiates Rh incompatibility in Rhesus disease?

<p>The sensitization of a Rh-negative mother to Rh-positive fetal blood.</p> Signup and view all the answers

What type of antibodies are primarily involved in Type II hypersensitivity reactions?

<p>IgM and IgG antibodies.</p> Signup and view all the answers

Which effector mechanisms are recruited in the destruction of red blood cells in IMHA?

<p>Complement-mediated lysis and antibody-dependent cellular cytotoxicity (ADCC).</p> Signup and view all the answers

In IMHA, where does hemolysis most commonly occur in dogs?

<p>Outside the bloodstream, particularly in the spleen, liver, and bone marrow.</p> Signup and view all the answers

What role do activated T cells play in macrophage activity?

<p>Activated T cells produce cytokines like IL-2 and IFN-gamma, which cause macrophages to aggregate into nodules.</p> Signup and view all the answers

What is the time frame for IgE-mediated hypersensitivity reactions to occur?

<p>IgE-mediated hypersensitivity reactions occur within 2-30 minutes.</p> Signup and view all the answers

Describe the mechanism of antibody-mediated cytotoxic hypersensitivity.

<p>Antibody-mediated cytotoxic hypersensitivity involves antibodies directed against cell-surface antigens that mediate cell destruction via ADCC or complement activation.</p> Signup and view all the answers

What causes the local and systemic reactions in immune complex-mediated hypersensitivity?

<p>In immune complex-mediated hypersensitivity, antigen-antibody complexes deposited at various sites induce degranulation of mast cells and PMN, leading to tissue damage.</p> Signup and view all the answers

What cytokines do memory TH1 cells release in cell-mediated hypersensitivity?

<p>Memory TH1 cells release cytokines that recruit and activate macrophages during cell-mediated hypersensitivity.</p> Signup and view all the answers

What is the significance of granulomas in the immune response?

<p>Granulomas represent a sustained immune response where activated macrophages and lymphocytes aggregate to contain pathogens.</p> Signup and view all the answers

What is the main mediator for mast cell degranulation in immune complex-mediated hypersensitivity?

<p>The main mediator for mast cell degranulation in immune complex-mediated hypersensitivity is FcgammaRIII.</p> Signup and view all the answers

List two examples of conditions that fall under IgE-mediated hypersensitivity.

<p>Two examples of IgE-mediated hypersensitivity are hay fever and asthma.</p> Signup and view all the answers

Study Notes

Immunopathology - Hypersensitivity

  • Hypersensitivity is the consequence of the immune system causing tissue damage.
  • Vaccination, transplantation, transfusion, tolerance generation, allergic reactions, immunodeficiency, and autoimmunity are all topics within immunopathology.

Types of Hypersensitivity

  • Gell and Coombs classified hypersensitivity reactions into 4 types.
  • Types I, II, and III are antibody-mediated.
  • Type IV is T cell-mediated.
  • Allergens are antigens that commonly cause hypersensitivity or allergic reactions.

Type I Hypersensitivity (Immediate)

  • Caused by contact with an antigen to which the host has a pre-existing IgE antibody.
  • IgE is present in low levels in serum (with a half-life of 2-3 days).
  • Much of the IgE in the body is bound to high-affinity receptors (FcεRI).
  • The bound state of IgE has a longer half-life (~3 weeks).
  • Mast cells, eosinophils, and basophils have high-density FcεRI receptors (40-250,000 per cell).
  • A wide spectrum of antigen specificities are represented.
  • Activation is via cross-linking of FcεRI receptors by antigen binding to bound IgE molecules.
  • Mast-cell activation and granule release leads to various symptoms, including:
    • Increased fluid secretion and peristalsis in the gastrointestinal tract
    • Decreased airways diameter and increased mucus secretion in the airways
    • Increased blood flow and permeability in blood vessels

Molecules Released by Mast Cells

  • Enzymes (e.g., tryptase, chymase, cathepsin G, carboxypeptidase)
  • Toxic mediators (e.g., histamine, heparin)
  • Cytokines (e.g., IL-4, IL-13)
  • Chemokines (e.g., CCL3)
  • Lipid mediators (e.g., prostaglandins D2, E2; leukotrienes B4, C4; platelet-activating factor)

Type II Hypersensitivity

  • Mediated by IgG, which engages Fc receptors and complement-mediated effector mechanisms.
  • Directed against cell-surface or matrix antigens.

Type III Hypersensitivity

  • Mediated by IgG directed against soluble antigens.
  • Tissue damage results from Fc receptor and complement-mediated effector mechanisms triggered by immune complexes.

Type IV Hypersensitivity

  • T cell-mediated.
  • Subdivided into three groups:
    • Tissue damage due to macrophage activation by TH1 cells
    • Damage caused by TH2 cell activation of inflammatory responses with eosinophils predominant
    • Damage directly caused by cytotoxic T cells (CTL)

Incidence and Genetic Susceptibility

  • Approximately 20-30% of the population exhibits type I hypersensitivity or atopic allergy to common environmental substances.
  • Genetic components play a significant role in atopic allergy.
    • Individuals with both atopic parents have a greater than 2x increased likelihood of susceptibility than compared to the overall population.
    • Individuals with neither atopic parent have less than 1/2 the likelihood of the general population susceptibility to atopic allergy.
  • Various genes influence sensitivity: IL-4, IL-4 receptors, high-affinity IgE receptor β-chain, MHC class II genes, T-cell receptor α locus, and others.

Clinical Aspects of Type I Hypersensitivity

  • Allergic rhinitis (hay fever)
  • Food allergies
  • Atopic (allergic) dermatitis
  • Asthma
  • Systemic anaphylaxis

Rhesus Disease

  • Caused by Rh incompatibility between mother and baby.
  • Results from a Rh-negative mother with Rh-positive antibodies towards a Rh-positive baby.
  • Can occur after mismatched blood transfusions or fetal blood entering the maternal circulation during miscarriage, abortion, placental bleeding, amniocentesis, or external cephalic version.

Goodpasture's Disease

  • Also known as Goodpasture Syndrome or anti-glomerular basement membrane (anti-GBM) disease.
  • Uncommon condition causing rapid kidney and lung destruction.
  • Anti-GBM antibodies bind to the glomerular basement membrane.
  • Treatment typically includes immunosuppressive drugs like steroids.

Myasthenia Gravis (MG)

  • Relatively rare autoimmune disorder of peripheral nerves.
  • Antibodies form against acetylcholine (ACh) nicotinic postsynaptic receptors at the myoneural junction.
  • Leads to a progressive reduction in muscle strength.
  • Thymic abnormalities are often associated with MG.

Hypersensitivity Prevention

  • Prevention is possible by vaccinating a Rh-negative mother with Rh immune globulin during pregnancy with Rh-positive fetus.

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Immunopathology - Hypersensitivity PDF

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Explore the intricate world of hypersensitivity in immunopathology through this engaging quiz. Learn about the four types of hypersensitivity reactions, their mechanisms, and their clinical implications. Test your understanding of antibody-mediated and T cell-mediated responses, along with the role of allergens in these processes.

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