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Questions and Answers
Which type of hypersensitivity reaction is characterized by a delayed immune response?
Which type of hypersensitivity reaction is characterized by a delayed immune response?
What is common across all types of hypersensitivity reactions?
What is common across all types of hypersensitivity reactions?
In which type of hypersensitivity reaction would you expect IgG or IgM antibodies binding to a cell surface?
In which type of hypersensitivity reaction would you expect IgG or IgM antibodies binding to a cell surface?
Which type of hypersensitivity reaction is primarily associated with asthma due to an allergic response?
Which type of hypersensitivity reaction is primarily associated with asthma due to an allergic response?
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What type of immune component is typically involved in hypersensitivity reactions?
What type of immune component is typically involved in hypersensitivity reactions?
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Which of the following statements is true about immune complexes in hypersensitivity reactions?
Which of the following statements is true about immune complexes in hypersensitivity reactions?
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Which characteristic distinguishes the primary response from the secondary response in hypersensitivity reactions?
Which characteristic distinguishes the primary response from the secondary response in hypersensitivity reactions?
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What type of hypersensitivity mechanism primarily involves T-cells?
What type of hypersensitivity mechanism primarily involves T-cells?
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Which of the following best describes the consequence of hypersensitivity reactions?
Which of the following best describes the consequence of hypersensitivity reactions?
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Which term describes the tendency of some individuals to develop IgE-mediated antibodies to allergens?
Which term describes the tendency of some individuals to develop IgE-mediated antibodies to allergens?
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What percentage of the population in developed countries is considered atopic?
What percentage of the population in developed countries is considered atopic?
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What is the primary immunoglobulin involved in Type I hypersensitivity reactions?
What is the primary immunoglobulin involved in Type I hypersensitivity reactions?
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Which of the following conditions is characterized by itchy raised swellings in response to an allergic reaction?
Which of the following conditions is characterized by itchy raised swellings in response to an allergic reaction?
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Which historical context best explains the term 'anaphylaxis'?
Which historical context best explains the term 'anaphylaxis'?
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What does the term 'allergen' specifically refer to?
What does the term 'allergen' specifically refer to?
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Seasonal Allergic Rhinitis affects what percentage of Canadians?
Seasonal Allergic Rhinitis affects what percentage of Canadians?
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Which food allergy prevalence statistic is noted for Canadians?
Which food allergy prevalence statistic is noted for Canadians?
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What does asthma primarily result from?
What does asthma primarily result from?
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The increase in allergy prevalence over the last 30 years has been quantified as?
The increase in allergy prevalence over the last 30 years has been quantified as?
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Study Notes
Overview of Hypersensitivity Reactions
- Hypersensitivity reactions (HSR) occur when the immune system reacts to an antigen in an exaggerated or harmful manner.
- Reactions can vary in severity, from mild to life-threatening.
- Hypersensitivity is categorized by the Gell and Coombs Classification—type I, II, III, and IV.
- Type I hypersensitivity reactions are immediate, often involving IgE antibodies, allergens and mast cells.
- Type II hypersensitivity reactions involve antibodies targeting cells or tissues.
- Type III hypersensitivity reactions involve the formation of immune complexes that deposit in tissues.
- Type IV hypersensitivity reactions are cell-mediated, delayed-type, and involve T cells.
Lecture Objectives
- Identify and distinguish the four types of hypersensitivity reactions (Types I-IV).
- Describe the immunological mechanisms underlying Type I hypersensitivity reactions.
- Describe the immunological mechanisms and pathophysiology underlying hypersensitivity type II reactions.
- Describe the immunological mechanisms and pathophysiology underlying hypersensitivity type III reactions.
- Describe the immunological mechanisms and pathophysiology underlying hypersensitivity type IV reactions.
Hypersensitivity Types I-IV
- Type I: Allergy/Anaphylaxis/Atopy—immediate hypersensitivity; involves IgE antibodies, mast cells, and basophils.
- Type II: Antibody-mediated—antibodies directed against cells or tissues.
- Type III: Immune complex—formation of antigen-antibody complexes that deposit in tissues.
- Type IV: Delayed-Type hypersensitivity (DTH)—cell-mediated; involves T cells and macrophages.
Common Hypersensitivity Reactions
- Adaptive immune response; Antigen is a protein (or a hapten or drug complexed with a protein or altered by a chemical group).
- Sensitization (primary response)
- A secondary, prolonged response.
Hypersensitivity Type I Reactions
- Case study—Allergic Asthma
- Definitions:
- Allergy—altered reactivity
- Allergen—an usually innocuous antigen stimulating an IgE antibody response leading to an allergic reaction in susceptible individuals.
- Atopy—propensity to develop IgE-mediated antibodies to allergens; ~40% of industrialized countries' population are atopic.
- Hives (urticaria)—raised swellings on the body from an allergic reaction.
- Asthma—chronic respiratory condition; hypersensitivity reaction (usually Type I allergy.)
- Anaphylaxis—immediate and exaggerated systemic allergic condition.
Common Allergens
- Inhaled: plant pollens, animal dander, mold spores, house dust mites.
- Injected: insect venoms, vaccines, drugs.
- Ingested: foods, orally administered drugs.
Three Phases of an Allergic Reaction
- Sensitization: Production of allergen-specific IgE that binds to IgE Fc receptors on mast cells and basophils.
- Activation: Re-exposure to the allergen; cross-linking of FcRs triggers rapid degranulation and release of potent inflammatory mediators.
- Effector: Response to inflammatory mediators released from activated mast cells; clinical manifestations (e.g., rhinitis, hives, asthma, anaphylaxis).
Additional Information
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Anaphylaxis—immediate, whole-body allergic reaction; symptoms and signs include puffy face/lips/tongue, urticaria, stridor, wheeze, hypotension, and collapse.
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Treatment for anaphylaxis—IM injection of 1:1000 adrenaline(epinephrine), 0.5 ml (adult/large child), 0.125ml-0.25ml (smaller children).
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Hypersensitivity Type II—case study—Hemolytic Disease of the Newborn (HDN) is a serious condition that occurs when there is an incompatibility between the blood types of a pregnant mother and her fetus. This often involves the Rh factor, an inherited protein found on the surface of red blood cells. When an Rh-negative mother carries an Rh-positive baby, her immune system may produce antibodies against the baby's red blood cells, leading to hemolysis (destruction of red blood cells) in the fetus or newborn, potentially resulting in severe anemia, jaundice, or even heart failure.
The disease can be detected through blood tests and ultrasound evaluations during pregnancy. Management may include monitoring the fetus, administering Rho(D) immune globulin to prevent the mother's immune response, or performing intrauterine transfusions in severe cases. Postnatally, treatments for HDN can involve phototherapy for jaundice or exchange transfusions if necessary. Early diagnosis and intervention are critical for ensuring the health of the newborn.
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Hypersensitivity Type III—case study—Serum sickness is an immune response that occurs after exposure to certain proteins in antiserum or monoclonal antibodies, leading to symptoms such as fever, rash, joint pain, and lymphadenopathy, typically appearing one to two weeks after exposure.
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Hypersensitivity Type IV—case study—Tuberculin, a purified protein derivative, is used to diagnose tuberculosis through intradermal administration, prompting an immune response in those previously exposed to Mycobacterium tuberculosis. Contact hypersensitivity is a delayed allergic reaction causing inflammation upon skin contact with allergens, relevant in allergic contact dermatitis. Understanding these concepts aids in effective immunology diagnosis and treatment.
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Description
This quiz covers the various types of hypersensitivity reactions as classified by Gell and Coombs. Participants will learn to identify and differentiate between Type I, II, III, and IV hypersensitivity, along with their immunological mechanisms. This content is essential for understanding allergic reactions and autoimmune disorders.
