Hypersensitivity Reactions Overview

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Questions and Answers

What type of hypersensitivity reaction primarily involves IgE antibodies?

Type IV hypersensitivity

Type I hypersensitivity (correct)

Type III hypersensitivity

Type II hypersensitivity

What is a common symptom associated with localized Type III hypersensitivity reactions?

Nasal congestion

Localized swelling and bleeding (correct)

Itchy rash all over the body

Severe migraines

Which of the following is a diagnostic test commonly used for detecting allergic reactions?

Skin prick test (correct)

Complete blood count

Urinalysis

Magnetic resonance imaging

What is a typical treatment option for managing allergic reactions?

Antihistamines Signup and view all the answers

Mast cell activation is primarily associated with which type of immune response?

Humoral immune response Signup and view all the answers

What is the main mechanism involved in delayed-type hypersensitivity (DTH)?

T-cell mediated response, primarily involving TH1 cells Signup and view all the answers

How is a positive delayed-type hypersensitivity reaction typically identified?

By a firm lesion developing within 48–72 hours after antigen injection Signup and view all the answers

What role do macrophages play in delayed-type hypersensitivity responses?

They promote granuloma formation through prolonged activation. Signup and view all the answers

Which of the following is NOT a typical sensitizing agent that can cause contact dermatitis?

Bacterial toxins Signup and view all the answers

What occurs during the initial exposure in a delayed-type hypersensitivity reaction?

Production of TH1 cells in response to the antigen Signup and view all the answers

What does a tuberculin skin test primarily indicate?

Previous sensitization to tuberculosis antigens Signup and view all the answers

Which cytokines are primarily involved in the effector phase of a delayed-type hypersensitivity reaction?

TH1 inflammatory cytokines Signup and view all the answers

What symptom typically results from the T-cell mediated response in contact dermatitis?

Rash with blister-like lesions Signup and view all the answers

What role do IgE antibodies play in type I hypersensitivity reactions?

They trigger mast cell degranulation. Signup and view all the answers

Which of the following symptoms is NOT typically associated with type I hypersensitivity reactions?

Rash due to drug toxicity Signup and view all the answers

Which diagnostic test is commonly used for identifying type I hypersensitivity reactions?

Skin prick testing Signup and view all the answers

Which treatment option is effective for managing acute allergic symptoms?

Antihistamines Signup and view all the answers

What triggers mast cell activation in an allergic reaction?

Cross-linking of Fcε receptors by allergens Signup and view all the answers

What type of mediators are released from mast cells upon activation?

Histamine, leukotrienes, and prostaglandins Signup and view all the answers

Which of the following allergens is most likely to elicit a type I hypersensitivity response?

Dust mites Signup and view all the answers

Which statement regarding IgE levels in allergic individuals is accurate?

IgE levels are typically elevated in atopic diseases. Signup and view all the answers

Which mechanism is primarily induced by the FcεRI receptor in allergic reactions?

Phosphorylation of ITAMs leading to allergic effects Signup and view all the answers

What component is NOT a known allergen associated with type I hypersensitivity?

Bacterial toxins Signup and view all the answers

What is the primary purpose of using ELISA in allergy diagnostics?

To assess total or allergen-specific IgE levels Signup and view all the answers

Which of the following describes the interaction between IgE antibodies and multivalent antigens in allergic individuals?

IgE antibodies cross-link with the antigens on mast cells. Signup and view all the answers

What is a significant risk associated with type I hypersensitivity reactions, particularly in severe cases?

Anaphylaxis Signup and view all the answers

Study Notes

Hypersensitivity Overview

Hypersensitivity is an undesirable reaction produced by the normal immune system, leading to allergies and autoimmune responses.
Reactions can be damaging, uncomfortable, or occasionally fatal.
Excessive immune response in sensitized individuals can result in tissue damage.

Types of Hypersensitivity

Four main types:
- Type I: Immediate (allergic reactions)
- Type II: Cytotoxic hypersensitivity
- Type III: Immune complex-mediated hypersensitivity
- Type IV: Delayed-type hypersensitivity (cell-mediated)

Type I Hypersensitivity

Involves IgE antibodies and is characterized as immediate and anaphylactic.
Allergies are initiated by interaction between IgE and a multivalent antigen.
Free circulating IgE is usually at low concentrations in healthy individuals.

Common Allergens

Plant pollens: Rye grass, ragweed, Timothy grass, Birch tree
Drugs: Penicillin, sulfonamides, local anesthetics, salicylates
Foods: Nuts, seafood, eggs, milk, peas, beans
Other allergens include insect products and dust mites.

Mechanism of Allergic Reactions

IgE antibodies cross-link Fcε receptors on innate immune cells (mast cells and basophils).
High-affinity IgE receptor (FcεRI) triggers allergic symptoms through signaling pathways.
Resulting mediators include histamine, leukotrienes, prostaglandins, and chemokines, causing various symptoms.

Symptoms and Diagnosis

Symptoms may include eczema, asthma, and anaphylaxis.
Skin testing is a common diagnostic method; it involves injecting small quantities of known allergens to observe swelling and redness.

Type II Hypersensitivity

Cytotoxic hypersensitivity involves complement activation and phagocyte involvement.

Type III Hypersensitivity

Characterized by immune complexes that are not cleared leading to inflammation and tissue damage.
Involves antigens from persistent infections, inhaled antigens, injected materials, and autoimmune reactions.
Examples: Serum sickness, systemic lupus erythematosus.

Immunocomplex Diseases

Immune complex injuries are dependent on the cause, antigen, and deposition sites (e.g., local inflammation in kidneys, lungs, or joints).

Type IV Hypersensitivity (DTH)

Purely cell-mediated and requires previous sensitization; T cells are the primary actors.
Characterized by macrophage recruitment, often demonstrated in conditions like contact dermatitis (e.g., poison ivy).
Detection involves skin tests, with positive responses indicating sensitized T cells.

Contact Dermatitis

Can be triggered by reactive chemicals binding to skin proteins, initiating a strong cell-mediated response.

Summary of Effects

Delayed-type hypersensitivity can result in granulomas and severe tissue damage if the antigen persists, as seen in conditions such as leprosy and tuberculosis.

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Description

This quiz explores the various types of hypersensitivity reactions caused by the immune system, including allergies and autoimmunity. Participants will learn about the different categories of reactions and their potential impacts, from discomfort to serious health risks. Test your understanding of how these immune responses can lead to tissue damage.