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Questions and Answers
What is one of the main roles of the complement system in hypersensitivity reactions?
What is one of the main roles of the complement system in hypersensitivity reactions?
Which autoimmune disease is characterized by auto-antibodies attacking the basement membranes of kidney glomeruli and lung alveoli?
Which autoimmune disease is characterized by auto-antibodies attacking the basement membranes of kidney glomeruli and lung alveoli?
In the context of hypersensitivity, what happens when cells are opsonized with autoantibodies?
In the context of hypersensitivity, what happens when cells are opsonized with autoantibodies?
What effect do antibodies against the Thyroid-Stimulating Hormone (TSH) receptor have in Graves disease?
What effect do antibodies against the Thyroid-Stimulating Hormone (TSH) receptor have in Graves disease?
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Why is splenectomy beneficial in certain autoimmune conditions such as autoimmune thrombocytopenia?
Why is splenectomy beneficial in certain autoimmune conditions such as autoimmune thrombocytopenia?
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What is the primary characteristic of type I hypersensitivity?
What is the primary characteristic of type I hypersensitivity?
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Which immune cells are primarily activated in the mechanism of type I hypersensitivity?
Which immune cells are primarily activated in the mechanism of type I hypersensitivity?
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What role does IL-4 play in type I hypersensitivity?
What role does IL-4 play in type I hypersensitivity?
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What is the initial event that triggers the type I hypersensitivity reaction?
What is the initial event that triggers the type I hypersensitivity reaction?
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What are potential clinical manifestations of type I hypersensitivity?
What are potential clinical manifestations of type I hypersensitivity?
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How do genes influence susceptibility to type I hypersensitivity?
How do genes influence susceptibility to type I hypersensitivity?
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What is the result of tissue destruction in hypersensitivity reactions?
What is the result of tissue destruction in hypersensitivity reactions?
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Why are some allergens harmful to certain individuals but not to the general population?
Why are some allergens harmful to certain individuals but not to the general population?
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What occurs upon re-exposure to the same allergen in immediate hypersensitivity reactions?
What occurs upon re-exposure to the same allergen in immediate hypersensitivity reactions?
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What is a key characteristic of anaphylactic shock?
What is a key characteristic of anaphylactic shock?
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Which of the following reactions is considered a type of localized hypersensitivity?
Which of the following reactions is considered a type of localized hypersensitivity?
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What is the role of IgG or IgM in Type II hypersensitivity?
What is the role of IgG or IgM in Type II hypersensitivity?
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How does bronchoconstriction occur during anaphylactic shock?
How does bronchoconstriction occur during anaphylactic shock?
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What defines a hapten in the context of Type II hypersensitivity?
What defines a hapten in the context of Type II hypersensitivity?
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Which of the following mechanisms is involved in Type II hypersensitivity when treating autoimmune thrombocytopenia?
Which of the following mechanisms is involved in Type II hypersensitivity when treating autoimmune thrombocytopenia?
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What is the primary result of liberation of mediators like histamine from mast cells?
What is the primary result of liberation of mediators like histamine from mast cells?
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Study Notes
Hypersensitivity Reactions (Lecture 29)
- Hypersensitivity reactions are immune responses that are harmful rather than helpful.
- They are classified into different types, including Type I (immediate) and Type II (cytotoxic).
- An initial exposure to an allergen can result in the production of IgE antibodies, which bind to mast cells.
- A subsequent encounter with the same allergen leads to the release of inflammatory mediators like histamine. This triggers allergic reactions.
- Examples of Type I hypersensitivity include anaphylactic shock (e.g., penicillin injection, bee venom) and local reactions like allergic rhinitis (hay fever) or bronchial asthma.
- Systemic reactions can include systemic vasodilation and a fall in blood pressure.
- Type II hypersensitivity involves antibodies (IgG or IgM) targeting antigens on cell surfaces.
- This can lead to cell destruction through several mechanisms.
- One mechanism involves targeting cells for phagocytosis, leading to conditions like autoimmune thrombocytopenia or hemolytic anemia (as in Goodpasture syndrome).
- Complement activation or interference with cellular function can also contribute to disease (as in Graves' disease).
Type I Hypersensitivity (Immediate)
- Characterized by a rapid response (within minutes) following allergen exposure.
- Involves IgE antibodies bound to mast cells.
- Allergens are environmental substances initially harmless, but some individuals are genetically predisposed to developing an allergic response.
- Th2 cells play a role in the production of IgE.
- The release of histamine and other chemical mediators triggers symptoms in subsequent exposures. This results in inflammation, vasodilation, bronchospasm, and increased mucus secretion.
Sequence of Events in Immediate Hypersensitivity
- First exposure: T-helper 2 (Th2) cells are activated. These cells release cytokines (e.g. IL-4, IL-5) that stimulate B cells.
- IgE antibodies are produced. IgE binds to mast cells.
- Subsequent Exposure: Allergen binds to IgE on mast cells.
- Mast cells release inflammatory mediators (e.g., histamine) triggering a cascade of reactions like vasodilation, bronchospasm, and mucus secretion.
Type II Hypersensitivity (Cytotoxic)
- Antibodies (IgG or IgM) are directed against antigens on cell surfaces.
- Mechanisms include cell targeting for phagocytosis (e.g., autoimmune hemolytic anemia), complement activation, or interference with normal cellular functions.
- Examples include Goodpasture syndrome (lungs and kidneys) and Graves' disease (thyroid).
Mechanisms of Type II Hypersensitivity
- Targeting cells for phagocytosis: Antibodies coat cells making them targets for neutrophils or macrophages.
- Complement activation: Antibody-complement activation leads to inflammation and cell destruction.
- Interfering with normal cellular functions: Antibodies can block receptor sites and interfere with normal cell function.
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Description
Explore the mechanisms and types of hypersensitivity reactions in this lecture. Learn how the immune system can respond harmfully to allergens and the specific pathways involved, including Type I and Type II reactions. Examples such as anaphylactic shock and allergic rhinitis are discussed to illustrate these concepts.
