Hypersensitivity and Type I Allergies

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Questions and Answers

What is the main immune mediator involved in type II hypersensitivity reactions?

IgA

Cytokines

IgM or IgG (correct)

IgE

Which of the following is NOT a clinical example of type II hypersensitivity?

Autoimmune hemolytic anemia

Myasthenia gravis

Goodpasture's syndrome

Rheumatoid arthritis (correct)

What characterizes type III hypersensitivity reactions compared to type II?

Occurs only after exposure to allergens

Involves only IgE antibodies

Involves soluble antigens (correct)

Involves T cells instead of antibodies

What is the main immunologic component involved in Type I hypersensitivity reactions?

IgE Signup and view all the answers

What is the role of complement in type II hypersensitivity?

It aids in opsonization and cell destruction. Signup and view all the answers

What mechanism is primarily responsible for the damage in serum sickness?

Antigen-antibody complex deposition Signup and view all the answers

Which of the following is NOT a clinical manifestation of Type I hypersensitivity?

Hemolytic anemia Signup and view all the answers

What is the timing of symptoms in type IV hypersensitivity?

Between 48 to 72 hours Signup and view all the answers

What feature distinguishes Type I hypersensitivity from other types?

Short time lag phase Signup and view all the answers

Which of the following statements about the Arthus reaction is true?

It involves immune complex formation in blood vessels. Signup and view all the answers

Which test is considered the preferred screening method for Type I hypersensitivity?

In-vivo skin prick test Signup and view all the answers

Which of the following is a characteristic of the immune mechanism in Type I hypersensitivity reactions?

Release of mediators from IgE-sensitized mast cells Signup and view all the answers

Which component is involved in the immune mechanism of type II hypersensitivity that leads to cell function inhibition?

Antibody binding Signup and view all the answers

What type of antigens trigger Type I hypersensitivity reactions?

Short allergens Signup and view all the answers

What is the timing of reactions in Type I hypersensitivity?

Immediate Signup and view all the answers

Type II hypersensitivity is primarily characterized by which type of immune response?

Antibody-mediated cytotoxicity Signup and view all the answers

Study Notes

Hypersensitivity

An exaggerated response to a typically harmless antigen that results in tissue injury, disease, or even death.
Gell and Coombs classified hypersensitivity reactions into four types based on the immunologic mechanism involved, the antibody, and the nature of the triggering antigen.
- Antibody-mediated: Type I, II, and III
- Cell-mediated: Type IV

Type I Hypersensitivity

Commonly referred as allergies
The antigens that trigger type I hypersensitivities are called allergens.
Distinguishing features: Short time lag phase.
Key Immunologic Components:
- IgE
- Basophils
- Mast cells
- Eosinophils

Type I Hypersensitivity Reaction

Immune Mediator: IgE
Synonym: Anaphylactic
Timing: Immediate
Antigen: Heterologous
Complement Involvement: No
Immune Mechanism: Release of mediators from IgE-sensitized mast cells and basophils.
Clinical Examples:
- Anaphylaxis
- Allergic Rhinitis
- Allergic Asthma
- Food Allergies
- Urticaria

Tests for Type I Hypersensitivity

In Vivo Skin Prick Test:
- Preferred screening test for allergies.
- Very small amounts of potential allergens are injected under the skin.
- Positive result: Wheal-and-flare reaction after 20 minutes.
Radioallergosorbent Test (RAST):
- A form of radioimmunoassay.
- A form of allergen-specific IgE testing.
Radioimmunosorbent Test (RIST):
- First test developed for the measurement of total IgE.

Type II Hypersensitivity

Also known as antibody-mediated cytotoxic hypersensitivity.
Involves IgG and IgM antibodies directed against antigens found on cell surfaces.

Type II Hypersensitivity Reaction

Immune Mediator: IgG or IgM.
Synonym: Antibody-mediated cytotoxicity.
Timing: Immediate.
Antigen: Autologous or heterologous, found on the cell surface.
Complement Involvement: Yes.
Immune Mechanism: Cell destruction caused by antibody and complement, opsonization, ADCC. Cell function inhibited by antibody binding.
Clinical Examples:
- Transfusion reactions
- Autoimmune hemolytic anemia
- Hemolytic disease of the newborn
- Drug reactions
- Myasthenia gravis
- Goodpasture's syndrome
- Graves' disease

Type III Hypersensitivity

Also known as immune complex hypersensitivity.
Similar to Type II, but antigens are soluble.

Type III Hypersensitivity Reaction

Immune Mediator: IgG or IgM.
Synonym: Complex-mediated.
Timing: Immediate.
Antigen: Soluble, heterologous or autologous.
Complement Involvement: Yes.
Immune Mechanism: Antigen-antibody complex activates complement proteins. Neutrophils are recruited and release lysosomal enzymes causing tissue damage.
Clinical Examples:
- Serum sickness
- Arthus reaction
- Lupus erythematosus
- Rheumatoid arthritis
- Drug reactions

Arthus Reaction

Immune complexes formed deposit on the walls of blood vessels, activating complement.

Serum Sickness

Results from passive immunization of humans with animal serum.
Humans develop antibodies against protein in the animal serum, antibodies combine with the protein forming complexes that can deposit in the tissues.

Type IV Hypersensitivity

First described by Robert Koch.
Sensitized T cells, rather than antibodies, play a major role.
Also known as delayed hypersensitivity because symptoms peak between 48-72 hours.

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Description

Explore the fascinating world of hypersensitivity, particularly focusing on Type I reactions, commonly known as allergies. This quiz covers the classification of hypersensitivity and key immunologic components involved in allergic reactions, including the roles of IgE, mast cells, and basophils.