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Questions and Answers
What type of hypersensitivity reaction is characterized by an immediate response after antigen interaction with IgE antibodies?
What type of hypersensitivity reaction is characterized by an immediate response after antigen interaction with IgE antibodies?
Which antibody is primarily involved in Type I hypersensitivity reactions?
Which antibody is primarily involved in Type I hypersensitivity reactions?
What is a necessary condition for an individual to develop a Type I hypersensitivity reaction?
What is a necessary condition for an individual to develop a Type I hypersensitivity reaction?
Which of the following is NOT an example of a common allergen that triggers Type I hypersensitivity reactions?
Which of the following is NOT an example of a common allergen that triggers Type I hypersensitivity reactions?
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What percentage of the population is estimated to be affected by Type I hypersensitivity reactions?
What percentage of the population is estimated to be affected by Type I hypersensitivity reactions?
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Which term describes the genetic predisposition associated with hypersensitivity reactions?
Which term describes the genetic predisposition associated with hypersensitivity reactions?
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Which type of hypersensitivity reaction is associated with immune complex-mediated disorders?
Which type of hypersensitivity reaction is associated with immune complex-mediated disorders?
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Which of the following is considered a Type IV hypersensitivity reaction?
Which of the following is considered a Type IV hypersensitivity reaction?
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Hypersensitivity reactions can be classified into how many main types?
Hypersensitivity reactions can be classified into how many main types?
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What is the primary consequence of antibodies formed against TSH receptors in Hashimoto thyroiditis?
What is the primary consequence of antibodies formed against TSH receptors in Hashimoto thyroiditis?
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Which of the following diseases is characterized by antibodies acting like TSH?
Which of the following diseases is characterized by antibodies acting like TSH?
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Which of the following is NOT an example of a type II hypersensitivity reaction?
Which of the following is NOT an example of a type II hypersensitivity reaction?
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In autoimmune hemolytic anemia, which component of blood is primarily affected?
In autoimmune hemolytic anemia, which component of blood is primarily affected?
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What type of antibodies are involved in the hyperacute rejection reaction?
What type of antibodies are involved in the hyperacute rejection reaction?
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Islet cell autoantibodies are indicative of which autoimmune condition?
Islet cell autoantibodies are indicative of which autoimmune condition?
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What is the primary role of TH2 cells during initial exposure to an antigen?
What is the primary role of TH2 cells during initial exposure to an antigen?
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What is the effect of IL-4 in the sensitization process?
What is the effect of IL-4 in the sensitization process?
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Which mediators are primarily responsible for the immediate phase response in type I hypersensitivity?
Which mediators are primarily responsible for the immediate phase response in type I hypersensitivity?
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What characterizes the late-phase reaction after allergen re-exposure?
What characterizes the late-phase reaction after allergen re-exposure?
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In type II hypersensitivity, what is the primary mechanism of cell damage during a complement-dependent reaction?
In type II hypersensitivity, what is the primary mechanism of cell damage during a complement-dependent reaction?
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What is one characteristic feature of an anaphylactic reaction?
What is one characteristic feature of an anaphylactic reaction?
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Which type of antibody is primarily involved in type II hypersensitivity reactions?
Which type of antibody is primarily involved in type II hypersensitivity reactions?
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How do antibodies mediate cellular dysfunction in type II hypersensitivity?
How do antibodies mediate cellular dysfunction in type II hypersensitivity?
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What role do mast cells play in the type I hypersensitivity response?
What role do mast cells play in the type I hypersensitivity response?
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What is a common example of localized type I hypersensitivity?
What is a common example of localized type I hypersensitivity?
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Study Notes
Hypersensitivity Reactions
- Definition: An exaggerated immune response to an antigen, resulting in tissue damage, disease, or even death.
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Characteristics:
- Priming: Prior exposure to the allergen is necessary for sensitization.
- Susceptibility: Genetic predisposition plays a crucial role, often linked to specific genes like HLA.
- Antigen: Virtually any substance that triggers an immune response can be an allergen.
- Origin: Antigens can be exogenous (external, e.g., pollen, food) or endogenous (internal, self-antigens).
Classification of Hypersensitivity Reactions
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Type I (Immediate):
- Also known as: Allergic or atopic disorders.
- Mechanism: Mediated by IgE antibodies bound to mast cells, leading to rapid reactions.
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Characteristics:
- Affects approximately 10-20% of the population.
- Reactions occur within minutes (5-10 minutes) after exposure.
- Elevated levels of IgE are found in individuals with atopic tendencies.
- Genetic predisposition is required, and the reaction is triggered by allergens.
- Examples: Bronchial asthma, hay fever, food allergies.
Type I Hypersensitivity Reaction Mechanisms
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Initial Exposure (Sensitization):
- Presentation: Antigen-presenting cells (APCs, like macrophages) present allergens to T cells.
- TH2 Activation: T cells differentiate into TH2 cells, secreting cytokines such as IL-4, IL-5, and IL-13.
- IgE Production: IL-4 stimulates B cells to produce IgE antibodies.
- Mast Cell Sensitization: IgE binds to Fc receptors on mast cells (located near blood vessels and nerves) and basophils.
- Note: No reaction occurs during the first exposure; sensitization takes time to develop.
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Re-exposure to Antigen:
- Cross-linking: The allergen binds to IgE on mast cells and basophils, causing their activation and degranulation.
- Mediator Release: Mast cells and basophils release preformed mediators (e.g., histamine, proteases, chemotactic factors), leading to immediate responses.
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Phases of IgE-Triggered Reactions:
- Immediate Phase: Occurs within 5-30 minutes and subsides within 60 minutes, characterized by vasodilation, increased vascular permeability, smooth muscle spasm, and glandular secretions.
- Late-Phase Reaction: Develops 2-8 hours after exposure and can last for days; characterized by tissue infiltration with various immune cells (eosinophils, neutrophils, basophils, monocytes, and TH2 cells) and mucosal epithelial cell damage.
Examples of Type I Hypersensitivity Reactions
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Localized Type I:
- Hay fever: Inflammation of the nasal and conjunctival mucosae, with sneezing and hypersecretion triggered by allergens like pollen.
- Extrinsic asthma: Wheezing and acute respiratory distress due to bronchospasm and increased mucus secretion caused by allergens such as house dust or animal dander.
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Systemic Type I (Anaphylaxis):
- Anaphylactic shock: Hypotension, widespread urticaria, and dyspnea, potentially fatal, often triggered by injected medications (e.g., penicillin) in sensitive individuals.
Antibody-Mediated (Type II) Hypersensitivity Reactions
- Definition: Antibodies bind to target cell surface antigens, causing cell lysis.
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Characteristics:
- Antibodies: Primarily IgG (occasionally IgM).
- Antigen: Can be endogenous (self-antigens) or exogenous (adsorbed on cell surfaces or altered by drug metabolites).
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Mechanisms of Injury:
- Complement Dependent: C3b and IgG or IgM activate complement, resulting in cell lysis (opsonization & phagocytosis).
- Antibody-Dependent Cellular Cytotoxicity (ADCC): Antibodies link natural killer cells or macrophages to target cells without phagocytosis or complement activation, leading to cell killing.
- Antibody-Mediated Cellular Dysfunction: Antibodies bind to cell surface receptors, disrupting function without causing cell injury or inflammation.
Examples of Type II Hypersensitivity Reactions
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Antibodies to Blood Cells:
- Autoimmune hemolytic anemia
- Transfusion reactions
- Hemolytic disease of the newborn (erythroblastosis fetalis)
- Idiopathic thrombocytopenic purpura (ITP)
- Drug-induced cytotoxic antibodies
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Antibodies to Tissue Components:
- Graves’ disease (hyperthyroidism)
- Myasthenia gravis
- Type 1 diabetes mellitus (islet cell autoantibodies)
- Hyperacute rejection reaction (antibodies against donor antigens)
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Description
Explore the various hypersensitivity reactions and their characteristics. Understand the mechanisms behind Type I hypersensitivity, including the role of IgE antibodies and the impact on affected individuals. This quiz will test your knowledge on the definitions and classifications of these immune responses.
