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Questions and Answers
What type of hypersensitivity reaction is characterized by an immediate allergic response, such as anaphylaxis?
What type of hypersensitivity reaction is characterized by an immediate allergic response, such as anaphylaxis?
Which of the following is a hallmark feature of Type 2 hypersensitivity?
Which of the following is a hallmark feature of Type 2 hypersensitivity?
What is the primary immune component involved in Type 3 hypersensitivity reactions?
What is the primary immune component involved in Type 3 hypersensitivity reactions?
Which disorder is most commonly associated with Type 1 hypersensitivity?
Which disorder is most commonly associated with Type 1 hypersensitivity?
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In managing allergic reactions, what is a primary intervention for anaphylaxis?
In managing allergic reactions, what is a primary intervention for anaphylaxis?
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What is the main mechanism behind Type 4 hypersensitivity?
What is the main mechanism behind Type 4 hypersensitivity?
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Which statement accurately describes the timing of Type 3 hypersensitivity reactions?
Which statement accurately describes the timing of Type 3 hypersensitivity reactions?
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Type 2 hypersensitivity primarily involves which type of antigens?
Type 2 hypersensitivity primarily involves which type of antigens?
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Which of the following describes the role of CD4 T cells in hypersensitivity reactions?
Which of the following describes the role of CD4 T cells in hypersensitivity reactions?
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Which type of hypersensitivity is commonly associated with autoimmune diseases?
Which type of hypersensitivity is commonly associated with autoimmune diseases?
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Which immune component is primarily involved in Type I hypersensitivity reactions?
Which immune component is primarily involved in Type I hypersensitivity reactions?
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What is the typical onset time for Type IV hypersensitivity reactions like contact dermatitis?
What is the typical onset time for Type IV hypersensitivity reactions like contact dermatitis?
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What is the primary mechanism involved in Type II hypersensitivity reactions?
What is the primary mechanism involved in Type II hypersensitivity reactions?
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Which allergic disorder is categorized under Type III hypersensitivity?
Which allergic disorder is categorized under Type III hypersensitivity?
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What is a common characteristic of Type III hypersensitivity?
What is a common characteristic of Type III hypersensitivity?
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What type of reactions do soluble haptens lead to in contact dermatitis?
What type of reactions do soluble haptens lead to in contact dermatitis?
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What cytokines are primarily produced in response to prior exposure to tuberculosis?
What cytokines are primarily produced in response to prior exposure to tuberculosis?
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Which response best describes the reaction at the injection site after TB testing?
Which response best describes the reaction at the injection site after TB testing?
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What is a major limitation of tests for prior exposure to tuberculosis?
What is a major limitation of tests for prior exposure to tuberculosis?
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In cases of allergic reactions involving anaphylaxis, which immune cells are primarily activated?
In cases of allergic reactions involving anaphylaxis, which immune cells are primarily activated?
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What is a key characteristic of Type I hypersensitivity reactions?
What is a key characteristic of Type I hypersensitivity reactions?
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Which of the following best describes the mechanism of Type III hypersensitivity?
Which of the following best describes the mechanism of Type III hypersensitivity?
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What is a common management strategy for anaphylactic reactions?
What is a common management strategy for anaphylactic reactions?
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Which of the following antigens typically triggers a Type II hypersensitivity reaction?
Which of the following antigens typically triggers a Type II hypersensitivity reaction?
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In Type I hypersensitivity, what role does histamine play?
In Type I hypersensitivity, what role does histamine play?
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What is the typical timeframe for symptoms to appear in a Type III hypersensitivity reaction?
What is the typical timeframe for symptoms to appear in a Type III hypersensitivity reaction?
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Which of the following conditions is primarily associated with Type I hypersensitivity?
Which of the following conditions is primarily associated with Type I hypersensitivity?
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In Type II hypersensitivity, what is the consequence of IgG or IgM binding to cell surface antigens?
In Type II hypersensitivity, what is the consequence of IgG or IgM binding to cell surface antigens?
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What is a major risk associated with anaphylaxis?
What is a major risk associated with anaphylaxis?
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What therapeutic approach is commonly used for Type I hypersensitivity management?
What therapeutic approach is commonly used for Type I hypersensitivity management?
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Study Notes
Hypersensitivity Reactions
- Hypersensitivity reactions are the consequence of an adaptive immune response.
- An initial stimulus (allergen/innocuous antigen) is required.
- Hypersensitivity is an overreaction of the immune system.
- Recognition of self and non-self antigens is crucial for immune function. Misidentification can lead to autoimmunity.
- Hypersensitivity reactions can be categorized, also known as Types I-IV based on the Gell and Coombs classification.
Objectives
- Diagram the pathophysiology of hypersensitivity reactions.
- Identify immune components, antigen types, mechanisms, and timing involved in hypersensitivity reactions.
- Correlate disorders with the appropriate hypersensitivity reaction type.
What is Hypersensitivity?
- The immune system can overreact to harmless substances, leading to hypersensitivity reactions.
- Examples include reactions to cat hair, allergies, and various other stimuli.
Normal Role of the Immune System
- The innate immune system provides a first line of defense through normal flora, skin, mucosal surfaces, and chemical factors.
- Components like complement and phagocytes (neutrophils, macrophages, and dendritic cells) are involved in local immune defense.
- Amplification of the immune response occurs through phagocytes, cytokines, and migration of dendritic cells.
- The adaptive immune system (B cells, specific antibodies, CD4 and CD8 T cells, and macrophages) contributes to clearing infections.
The True Nature of the Immune System
- The immune system defends against both friend (self) and foe (foreign).
- It works by recognizing antigens, including self-antigens that can trigger autoimmunity.
- Oversensitivity to innocuous or otherwise harmless antigens leads to hypersensitivity reactions.
Hypersensitivity & Allergies Fundamentals
- All hypersensitivities are a consequence of an adaptive immune response.
- An initiating antigen (e.g., allergen/innocuous antigen) triggers this overreaction.
- Adaptive immune response leads to the development of memory, enabling subsequent reactions.
Gell and Coombs Classification
- Type I: IgE-mediated (anaphylaxis)
- Type II: Antibody-dependent cellular cytotoxicity (e.g., Hemolytic disease of the newborn)
- Type III: Immune complex-mediated (e.g., serum sickness, SLE)
- Type IV: Cell-mediated (delayed-type) (e.g., contact dermatitis, PPD)
Type I Hypersensitivity (Anaphylaxis)
- Antigens are typically soluble (e.g., peanuts, pollen, animal dander).
- Initial exposure introduces innocuous antigens, recognized as foreign.
- Type I response involves IgE generation, binding to mast cells/basophils via FcεRI receptors.
- Subsequent exposure triggers mast cell degranulation, releasing histamine and other mediators.
- This response produces inflammation and anaphylaxis.
- Causes of anaphylaxis commonly involve ingested food, medications or insect stings.
- Systemic reactions can be life-threatening.
Type II Hypersensitivity (Cytotoxic)
- Antigens are frequently cell surface antigens (e.g., Rh and ABO antigens on RBCs).
- Initial exposure recognized as foreign leads to IgG or IgM generation by plasma cells.
- Subsequent exposure causes IgG/IgM binding to cell surface antigens, triggering complement activation.
- This can lead to antibody-dependent cellular cytotoxicity and inflammation.
- Common examples include acute hemolytic transfusion reactions and hemolytic disease of the newborn.
Type III Hypersensitivity (Immune Complex)
- Antigens are typically soluble (e.g., anti-venom, self-DNA).
- Initial exposure recognized as foreign, leading to IgG generation in plasma cells.
- Subsequent exposure causes IgG binding to soluble antigens, forming immune complexes.
- These complexes deposit in tissues, activating complement and inflammatory responses.
- Examples include serum sickness and Systemic Lupus Erythematosus (SLE).
Type IV Hypersensitivity (Delayed-Type)
- Antigens can be soluble (e.g., poison ivy, metals, dyes, tuberculin) or cell surface antigens (e.g., granulomatous hypersensitivity).
- Initial exposure leads to activation of cellular immunity.
- The subsequent exposure causes memory T cells to recognize antigen.
- This involves activation of the Th1 pathway, cytokines (IFN-γ, TNF-α) and CD8+ and macrophage activation, leading to inflammation.
- Common examples include contact dermatitis and the tuberculin skin test (PPD).
Hypersensitivity Management
- Management depends on the specific hypersensitivity condition.
- Treatments include antihistamines, corticosteroids, mast cell stabilizers, and epinephrine.
- Allergen immunotherapy, also known as desensitization, is an option in some cases (e.g., subcutaneous or sublingual).
Summary & Review
- A summary of different hypersensitivities, including the immune components, antigens, mechanisms, timeframes and associated disorders is provided.
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Description
Explore the types and mechanisms of hypersensitivity reactions as part of your immunology studies. This quiz covers the pathophysiology, immune components, and correlation of disorders with hypersensitivity reaction types. Test your understanding of how the immune system can misidentify antigens and lead to an overreaction.
