Immunology Type II Hypersensitivity Quiz

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Questions and Answers

What type of antibodies are primarily involved in Type II hypersensitivity reactions?

IgA or IgD

IgM or IgG (correct)

IgE or IgG

IgG or IgM

Which of the following is an example of a cytotoxic Type II hypersensitivity reaction with inflammation?

Myasthenia gravis

Graves' disease

Rheumatic heart disease (correct)

Drug-induced hemolytic anemia

In non-cytotoxic Type II hypersensitivity reactions, the binding of antibodies influences which aspect of cell function?

Cell proliferation

Cell adhesion

Cell metabolism

Cell signaling (correct)

Which mechanism is primarily responsible for cell destruction in cytotoxic Type II hypersensitivity reactions?

Antibody-dependent cell-mediated cytotoxicity (ADCC) Signup and view all the answers

Which condition is a classic example of a non-cytotoxic Type II hypersensitivity reaction?

Graves' disease Signup and view all the answers

Which cytokines are primarily involved in amplifying the Th2 response?

IL-4 and IL-13 Signup and view all the answers

What is a significant drawback of the skin prick test for diagnosing type I hypersensitivity reactions?

May induce systemic anaphylactic shock Signup and view all the answers

What role do eosinophils play in type I hypersensitivity reactions?

They participate in late-phase reactions Signup and view all the answers

What is the mechanism of action for humanized monoclonal anti-IgE antibodies in immunotherapy?

They bind to Fc region of IgE and block its receptor binding Signup and view all the answers

Which of the following cytokines is associated with increasing cell adhesion molecule expression on endothelial cells?

TNF-α Signup and view all the answers

What is a key feature of the immediate early response in type I hypersensitivity?

Results from mast cell degranulation Signup and view all the answers

What is the main function of leukotrienes produced via the lipoxygenase pathway?

Facilitate chemotaxis for immune cells Signup and view all the answers

Which test measures IgE levels in a patient's serum to diagnose allergies?

IgE test Signup and view all the answers

Which cytokines are predominantly involved in the type 2 immune responses during the sensitization phase of type I hypersensitivity?

IL-4, IL-5, IL-13 Signup and view all the answers

What is the primary role of IgE antibodies in type I hypersensitivity reactions?

They cross-link with allergens, triggering mast cell degranulation. Signup and view all the answers

Which of the following is NOT a typical environmental allergen that can trigger type I hypersensitivity reactions?

Viruses Signup and view all the answers

Which phase of hypersensitivity reactions is characterized by the absence of symptoms upon initial exposure to the allergen?

Sensitization phase Signup and view all the answers

What triggers mast cells to release their chemical mediators during the allergic phase of type I hypersensitivity?

The cross-linking of IgE molecules by the allergen Signup and view all the answers

What is the role of phospholipase A2 (PLA2) in the synthesis of newly synthesized lipid mediators during type I hypersensitivity?

It catalyzes the formation of arachidonic acid from membrane phospholipids. Signup and view all the answers

In diagnosing type II hypersensitivity diseases, which of the following tests is commonly used?

Direct Coombs test Signup and view all the answers

Which immune cells are primarily involved in type I hypersensitivity reactions mediated by IgE?

Mast cells, basophils, and eosinophils Signup and view all the answers

Study Notes

Hypersensitivity Reactions

Type II hypersensitivity reactions are antibody-mediated and involve IgM or IgG antibodies directed against antigens on cells or extracellular matrix.
These antibodies are tissue-specific and do not typically circulate systemically.

Type II Hypersensitivity Subtypes

Cytotoxic Reactions: antibodies activate complement, mediate cell destruction through antibody-dependent cell-mediated cytotoxicity (ADCC), or opsonize cells.
- Examples: blood transfusion reactions, drug-induced hemolytic anemia, and hemolytic anemia of newborns.
- Drug-induced hemolytic anemia occurs when individuals produce antibodies against drugs or their metabolites attached to red blood cell proteins, leading to hemolysis.
- Rheumatic heart disease, characterized by antibodies attacking heart valve proteins, is an example of a type II hypersensitivity reaction with inflammation.
Non-Cytotoxic Reactions: antibody binding to antigens affects cell function, either stimulating or inhibiting it.
- Examples: Graves’ disease and myasthenia gravis.

Type I Hypersensitivity Reactions (IgE-Mediated)

Characterized by an exaggerated immune response against harmless environmental antigens (allergens), leading to tissue injury.
Common allergens include plant pollens, drugs, dust, dust mites, animal dander, and food.

Pathogenesis

Sensitization Phase:
- Antigen-presenting cells (APCs) engulf, process, and present allergens in association with MHC Class II molecules to naïve T helper cells.
- Naïve T helper cells differentiate into Th2 and Tfh cells in individuals with allergies.
- Th2 and Tfh cells secrete IL-4, IL-5, and IL-13, collectively known as type 2 immune responses.
- IL-4 induces B cell growth and switching from IgM to IgE isotype.
- IgE antibodies bind to high-affinity IgE receptors on mast cells and basophils.
Allergic Phase:
- Upon re-exposure to the allergen, it cross-links sufficient IgE molecules, triggering mast cell degranulation and the release of chemical mediators.

Chemical Mediators

Preformed Mediators: released immediately upon mast cell degranulation are involved in the immediate early response.
Newly Synthesized Lipid Mediators: synthesis is controlled by activation of phospholipase A2 (PLA2), which hydrolyzes membrane phospholipids to generate arachidonic acid.
- Arachidonic acid is metabolized via the cyclooxygenase pathway (producing prostaglandins) or the lipoxygenase pathway (producing leukotrienes).
- Prostaglandins and leukotrienes are potent vasodilators, bronchoconstrictors, chemotactic factors for eosinophils, basophils, and Th2 cells, and stimulators of mucus secretion.
Cytokines: IL-1, IL-3, IL-4, IL-5, IL-13, and TNF are released and contribute to late-phase reactions (2-8 hours).
- IL-4 and IL-13 amplify Th2 response, while IL-3 and IL-5 promote eosinophil production and activation.

Type I Hypersensitivity Responses

Characterized by immediate early and late-phase responses.
Early Response: occurs within minutes of allergen exposure due to mast cell degranulation and release of preformed and lipid mediators.
Late-Phase Response: (2-8 hours) involves the recruitment of eosinophils, neutrophils, and Th2 cells due to cytokine release from mast cells, primarily TNF-α and IL-1.

Diagnosis of Type I Hypersensitivity Reactions

Skin Prick Test: small amounts of potential allergens are introduced into the skin. A positive reaction (wheal and flare within 30 minutes) indicates an allergic response.
- Disadvantages: can sensitize individuals to new allergens, rarely induce systemic anaphylaxis, manifest late-phase reactions, and produce false-negative results in individuals taking antihistamines.
IgE Test: measures IgE levels in serum.

Immunotherapy for Allergy

Humanized monoclonal anti-IgE antibody: binds to the Fc portion of IgE and blocks its binding to IgE receptors on mast cells.
Desensitization: repeated subcutaneous injections of small quantities of the antigen induce the production of IgG antibodies. This reduces the sensitivity to allergens by reducing the amount IgE antibodies in the system.

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Description

Test your knowledge on Type II hypersensitivity reactions, their mechanisms, and subtypes. This quiz covers cytotoxic and non-cytotoxic reactions, including examples like blood transfusion reactions and drug-induced hemolytic anemia. Assess your understanding of the antibody-mediated immune responses and their clinical implications.