Types of Immune Response: Hypersensitivity I & II

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Questions and Answers

What characterizes Type I hypersensitivity reactions?

They are immune responses that do not involve prior sensitization to the antigen.

They are delayed-type reactions that take several days to develop.

They involve immediate immunologic reactions mediated by immunoglobulin E (IgE) bound to mast cells. (correct)

They occur due to the combination of an antigen with immunoglobulin M (IgM) in sensitized individuals.

Which of the following best describes the term 'Atopy'?

An autoimmune disorder characterized by overactive T cells.

A genetically determined susceptibility to allergic reactions. (correct)

A deficiency in immunoglobulin production.

An immediate hypersensitivity reaction to food antigens only.

Which of the following conditions is most commonly associated with Type I hypersensitivity?

Rheumatoid arthritis and lupus erythematosus.

Blood group incompatibility reactions.

Type II diabetes and metabolic syndrome.

Anaphylaxis and allergic rhinitis. (correct)

In the context of hypersensitivity reactions, which statement about Type II reactions is correct?

They can result in damage to tissue due to antibody-binding to the surface of target cells. Signup and view all the answers

What is a key factor contributing to the development of hypersensitivity diseases?

Inherited susceptibility genes associated with abnormal immune responses. Signup and view all the answers

What initiates the early phase reaction in a type I hypersensitivity response?

Introduction of an allergen leading to IgE production Signup and view all the answers

Which cytokine is considered the most potent for activating eosinophils in the late-phase reaction?

IL-5 Signup and view all the answers

What is a characteristic feature of the late-phase reaction in type I hypersensitivity?

Recruited eosinophils causing tissue damage Signup and view all the answers

Which of the following is NOT a chemical mediator released during a type I hypersensitivity reaction?

Cytokine IL-2 Signup and view all the answers

Which effector cell primarily responds to allergens in type I hypersensitivity reactions?

Mast cells Signup and view all the answers

What clinical manifestation is commonly associated with anaphylactic shock?

Hoarseness due to laryngeal edema Signup and view all the answers

What role do T helper-2 cells play in type I hypersensitivity?

They stimulate IgE production upon allergen exposure. Signup and view all the answers

Which of the following allergic stimuli can trigger a type I hypersensitivity reaction?

Food allergens Signup and view all the answers

What is a common effect of histamine release during the early phase of a type I hypersensitivity reaction?

Enhanced vascular permeability and edema Signup and view all the answers

What occurs during the degranulation of mast cells upon second exposure to an allergen?

Release of primary mediators causing clinical symptoms Signup and view all the answers

Study Notes

Types of Immune Response: Type I & II Hypersensitivity Reactions

Abnormal immune responses are called hypersensitivity reactions
Hypersensitivity is an exaggerated response to harmless antigens
Imbalance between effector and regulatory mechanisms cause hypersensitivity
Individuals previously exposed, or sensitized, to an antigen can develop hypersensitivity reactions
Reactions can result from exogenous or endogenous antigens
Types I, II, and III are immediate (chemical) reactions within 24 hours
Type IV is a cellular reaction that takes several days

Type I Hypersensitivity (Atopy/Allergy)

Rapidly developing immune reaction
Antigen combines with IgE bound to mast cells in sensitized individuals
Also known as anaphylactic reaction
Allergy is an abnormal adaptive immune response, potentially involving antigen-specific IgE

Type I Hypersensitivity Mechanism

Early phase (5-30 minutes): Allergen exposure triggers T helper 2 (Th2) cells and IgE production in genetically susceptible individuals
IgE binds to mast cell Fc receptors. Subsequent allergen exposure leads to mast cell degranulation
Degranulation releases chemical mediators (histamine, leukotrienes, prostaglandins)
Resulting effects include increased vascular permeability, smooth muscle contraction (e.g., bronchospasm), and other symptoms.
Late phase (4-12 hours): Neutrophils, eosinophils, and lymphocytes recruited by mast cell mediators
TH2 cytokine IL-5 activates eosinophils
Tissue damage and late-phase inflammation results

Clinical Examples of Type I Hypersensitivity

Systemic anaphylaxis (anaphylactic shock)
Allergic rhinitis (hay fever)
Asthma
Food allergies
Atopic dermatitis

Type II Hypersensitivity (Cytotoxic Hypersensitivity)

Antibodies (primarily IgG and sometimes IgM) bind to antigens on cell surfaces or other tissue components
This leads to cell destruction, inflammation, or altered function
Three mechanisms:
- Opsonization and phagocytosis
- Complement- and Fc receptor-mediated inflammation
- Antibody-mediated cellular dysfunction

Clinical Examples of Type II Hypersensitivity

Hemolytic transfusion reaction
Hemolytic disease of the newborn (erythroblastosis fetalis)
Autoimmune anemia
Drug reactions

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Description

Explore the different types of hypersensitivity reactions, focusing on Type I and Type II responses. This quiz covers the mechanisms, triggers, and outcomes associated with abnormal immune responses, including allergic reactions and their biological basis. Test your knowledge on these crucial immunological concepts.