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Hypersensitivity Reactions: Immunology and Allergies
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Hypersensitivity Reactions: Immunology and Allergies

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Questions and Answers

What is hypersensitivity defined as?

  • A desirable reaction produced by the immune system
  • An exaggerated response to a typically harmless antigen that results in injury to the tissue, disease, or even death (correct)
  • A response that only occurs in people with weak immune systems
  • A normal immune response to an antigen

    • What type of hypersensitivity reaction is also known as anaphylaxis?

  • Type III: Immune complex
  • Type IV: Cell mediated, delayed
  • Type II: Cytotoxic or cytolytic
  • Type I: Immediate (correct)

    • What is the mechanism involved in Type I hypersensitivity?

  • Phagocytosis or lyses of cells
  • Activation of the complement system
  • Release of cytokines and cytolytic enzymes
  • Immediate release of mediators by basophils and mast cells (correct)

    • What is the result of an exaggerated immune response in hypersensitivity?

    <p>Injury to the tissue, disease, or even death</p> Signup and view all the answers

    Which type of hypersensitivity reaction involves immune complexes?

    <p>Type III: Immune complex</p> Signup and view all the answers

    What is the term for protection in Greek?

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

    What type of antibodies are involved in Type I hypersensitivity?

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

    What is a characteristic of Type IV hypersensitivity?

    <p>It is a cell-mediated, delayed response</p> Signup and view all the answers

    Which type of immune response is associated with allergies?

    <p>Th2 response</p> Signup and view all the answers

    What is the primary function of mast cells?

    <p>To store and release inflammatory mediators</p> Signup and view all the answers

    What is the primary difference between mast cells and basophils?

    <p>Basophils have larger granules</p> Signup and view all the answers

    What is the role of IL-4 in the immune response?

    <p>To initiate B cell differentiation</p> Signup and view all the answers

    What is the receptor found on mast cells that specifically binds IgE?

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

    What is the approximate percentage of basophils in peripheral blood?

    <p>Less than 1%</p> Signup and view all the answers

    What genetic factor is associated with atopic allergies?

    <p>IL-4 gene variant</p> Signup and view all the answers

    What type of hypersensitivity reaction is associated with mast cells and basophils?

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

    What is the primary function of Eosinophil chemotactic factor of anaphylaxis (ECF-A)?

    <p>To attract eosinophils to the site of allergic reaction</p> Signup and view all the answers

    What is the effect of histamine on human bronchioles?

    <p>Contraction of smooth muscle</p> Signup and view all the answers

    What is the role of eosinophils in allergic reactions?

    <p>To control allergic reactions by releasing histaminase and arylsulfatase</p> Signup and view all the answers

    What is the effect of serotonin on blood vessels?

    <p>Dilation of capillaries</p> Signup and view all the answers

    Which of the following is a secondary mediator?

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

    What is the effect of proteases on blood vessels?

    <p>Vasodilation and increased permeability</p> Signup and view all the answers

    Which of the following is a clinical manifestation of type I hypersensitivity reaction?

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

    What is the role of neutrophil chemotactic factor?

    <p>To attract neutrophils to the site of allergic reaction</p> Signup and view all the answers

    Why should patients avoid taking antihistamine before the Skin Prick Allergy Test?

    <p>To prevent interference with the test results</p> Signup and view all the answers

    What is the purpose of PRIST in allergy testing?

    <p>To detect total IgE levels</p> Signup and view all the answers

    Which medication is used to stabilize mast cells and basophils?

    <p>Sodium chromoglycate</p> Signup and view all the answers

    What is the ultimate goal of immunotherapy in allergy treatment?

    <p>To shift the immune response to a Th1-type response</p> Signup and view all the answers

    What is the role of T regulatory cells in immunotherapy?

    <p>To produce IL-10 and regulate the immune response</p> Signup and view all the answers

    What is the purpose of injecting small doses of the allergen in desensitization therapy?

    <p>To desensitize the patient and reduce allergic symptoms</p> Signup and view all the answers

    What is the typical duration of desensitization therapy?

    <p>4 years</p> Signup and view all the answers

    What is the mechanism by which IgG4 blocking antibody prevents allergic reactions?

    <p>By combining with the allergen and preventing IgE binding</p> Signup and view all the answers

    What is the main difference between anaphylactic and anaphylactoid reactions?

    <p>Anaphylactic reactions are IgE-mediated, while anaphylactoid reactions are not.</p> Signup and view all the answers

    What is the primary cause of fatalities in anaphylactic reactions?

    <p>Loss of fluid from the bloodstream into tissues</p> Signup and view all the answers

    Which of the following is a common food that can cause anaphylaxis?

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

    What is the purpose of the Skin Prick Allergy Test?

    <p>To diagnose allergies</p> Signup and view all the answers

    What is the typical timeframe for an allergic reaction to appear in the Skin Prick Allergy Test?

    <p>15 minutes</p> Signup and view all the answers

    Which of the following drugs is known to cause type I allergic reactions?

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

    What is the primary source of mediators in anaphylactic reactions?

    <p>Mast cells and basophils</p> Signup and view all the answers

    What percentage of anaphylactoid reactions are idiopathic?

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

    Study Notes

    Hypersensitivity Reactions

    • Hypersensitivity reactions are exaggerated responses to typically harmless antigens, resulting in injury, disease, or even death.
    • These reactions are undesirable and can be damaging, uncomfortable, or occasionally fatal.

    Types of Hypersensitivity Reactions

    • Hypersensitivity reactions can be divided into four types based on the mechanisms involved and the time taken for the reaction: • Type I: Immediate, anaphylactic • Type II: Cytotoxic or cytolytic • Type III: Immune complex • Type IV: Cell-mediated, delayed

    Antibody-Mediated Hypersensitivity

    • Types I, II, and III are antibody-mediated hypersensitivity reactions
    • These reactions involve the activation of B cells and the production of IgE antibodies

    Cell-Mediated Hypersensitivity

    • Type IV is a cell-mediated hypersensitivity reaction
    • This reaction involves the activation of T cells and the production of cytokines

    Causes of Tissue Injury in Hypersensitivity Reactions

    • Release of vasoactive materials
    • Phagocytosis or lysis of cells
    • Activation of the complement system
    • Release of cytokines and cytolytic enzymes

    Type I Hypersensitivity (Anaphylaxis)

    • Also known as immediate hypersensitivity
    • The most common form of hypersensitivity reactions
    • Mediated by IgE antibodies and produced by the immediate release of mediators by basophils and mast cells
    • Exposure to allergens can be through ingestion, inhalation, injection, or direct contact

    Th1 and Th2 Cells

    • In normal immune responses, there is a balance between Th1 and Th2 cells
    • In allergic individuals, the immune response is shifted towards Th2 cells, leading to the production of IgE antibodies

    Mast Cells

    • The principal effector cells of immediate hypersensitivity reactions
    • Found throughout the body, particularly in areas around small blood vessels, lymphatics, nerves, and glandular tissue
    • Have abundant cytoplasmic granules that store preformed inflammatory mediators

    Basophils

    • Similar to mast cells, but distinct in terms of appearance and function
    • Present in peripheral blood, representing less than 1% of total white blood cells
    • Have fewer, but larger granules than mast cells, and the concentrations of inflammatory substances in the granules differ from those of mast cells

    Factors Predisposing to Type I Hypersensitivity

    • Genetic factors, such as atopic allergies (hay fever, asthma, food allergy)
    • Atopic individuals have an IL-4 gene that codes for high levels of IL-4

    Primary Mediators

    • Histamine: the most important vasoactive amine of human anaphylaxis, leading to burning, itching, and other symptoms
    • Eosinophil chemotactic factor of anaphylaxis (ECF-A): attracts eosinophils, which are prominent in immediate allergic reactions
    • Neutrophil chemotactic factor: attracts neutrophils to the site of allergic reaction
    • Serotonin: causes capillary dilation, increased vascular permeability, and smooth muscle contraction
    • Proteases: causes vasodilation and increased permeability

    Secondary Mediators

    • Leukotriene: slow-reacting substance of anaphylaxis (SRSA), leading to bronchoconstriction, hypotension, and vascular permeability
    • Prostaglandins: causes bronchoconstriction, hypotension, and vascular permeability
    • Platelet-activating factors (PAF): causes bronchoconstriction, hypotension, and vascular permeability

    Clinical Manifestations of Type I Hypersensitivity Reaction

    • Asthma
    • Allergic conjunctivitis
    • Rhinitis (hay fever)
    • Atopic dermatitis (atopic eczema)
    • Urticaria (hives)/angioedema

    Systemic Anaphylaxis (Anaphylactic Shock)

    • The most severe form of type I hypersensitivity, characterized by severe bronchoconstriction and hypotension (shock) that can be life-threatening
    • Antigen enters the bloodstream, leading to widespread reaction and affecting almost the entire body
    • Loss of fluid from blood vessels into tissues causes swelling and possibly shock

    Anaphylactoid Reactions

    • Result from systemic release of mediators from mast cells and basophils
    • Mimic signs and symptoms of anaphylaxis
    • Not IgE-mediated, but occur at the first contact with the inciting agent
    • Inciting agents include drugs, iodinated media, vigorous exercise, contrast media, and others

    Diagnosis of Type I Hypersensitivity Reaction

    • Medical history
    • Skin Prick Allergy Test: involves putting a drop of liquid containing a substance onto the forearm, and then gently pricking the skin with a needle
    • Detection of total and specific IgE: using Paper Radioimmunosorbent Test (PRIST) and Radioallergosorbent test (RAST) or Enzyme-linked immunosorbent assay (ELISA)

    Treatment of Type I Hypersensitivity Reaction

    • Allergen avoidance
    • Drugs: anti-histamines, mast cell and basophil stabilizing drugs, and general anti-inflammatory agents
    • Immunotherapy: desensitization (hyposensitization) using allergy shots, which involves weekly injections of very small doses of the allergen for the first year, and then gradually decreasing to monthly injections.

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    Description

    This quiz covers hypersensitivity reactions, including exaggerated immune responses, tissue damage, and diseases related to allergies and autoimmunity. Test your knowledge of immunological responses and their consequences.

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