Hypersensitivity and Autoimmunity
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Questions and Answers

Which type of hypersensitivity reaction is primarily associated with IgE antibodies?

  • Type III
  • Type II
  • Type I (correct)
  • Type IV

Which condition is commonly categorized under Type II hypersensitivity reactions?

  • Food allergies
  • Contact dermatitis
  • Asthma
  • Hemolytic transfusion reactions (correct)

What type of hypersensitivity reaction is characterized by immune complexes?

  • Type III (correct)
  • Type I
  • Type II
  • Type IV

Koch's phenomenon is an example of which type of hypersensitivity reaction?

<p>Type IV (A)</p> Signup and view all the answers

Which diagnosis method is employed to identify allergies in patients?

<p>Skin prick test (A)</p> Signup and view all the answers

What can result from exposure to normally sequestered antigens during development?

<p>Autoimmune disease (A)</p> Signup and view all the answers

How can structural modification of tissue proteins lead to autoimmune disease?

<p>By creating autoantibodies that target modified proteins (C)</p> Signup and view all the answers

What does cross-reactivity refer to in the context of autoimmune diseases?

<p>Antibodies targeting both foreign and self-antigens (D)</p> Signup and view all the answers

What is an example of an autoimmune disease caused by the modification of surface proteins?

<p>Autoimmune hemolytic anemia (C)</p> Signup and view all the answers

What is the primary mechanism behind autoimmune diseases resulting from exposure to normally hidden antigens?

<p>Survival of unmatured lymphocytes (C)</p> Signup and view all the answers

What characterizes type IV hypersensitivity?

<p>Responses are mediated by T-cells and macrophages (B)</p> Signup and view all the answers

In immune complex-mediated hypersensitivity, what is a primary mechanism of tissue damage?

<p>Deposition of immune complexes leading to inflammation (C)</p> Signup and view all the answers

What is the typical time frame for reactions in type I hypersensitivity?

<p>15-30 minutes (B)</p> Signup and view all the answers

Which of the following describes the role of macrophages in delayed hypersensitivity reactions?

<p>Engulf antigens and present them to T-cells (B)</p> Signup and view all the answers

Which immunological response is characterized by the presence of serum sickness and systemic lupus erythematosus (SLE)?

<p>Type III hypersensitivity (D)</p> Signup and view all the answers

What is the hallmark of autoimmune diseases related to autotolerance failure?

<p>Immune response against self-antigens (C)</p> Signup and view all the answers

What type of hypersensitivity is characterized by complement activation and cell destruction via antibodies?

<p>Type II hypersensitivity (B)</p> Signup and view all the answers

What is a major characteristic of the Arthus reaction?

<p>Development of localized swelling and redness (A)</p> Signup and view all the answers

Which of the following best describes acquired (induced) tolerance?

<p>Induced at any time in life (A)</p> Signup and view all the answers

Which cell type is primarily involved in type III hypersensitivity reactions?

<p>Neutrophils (C)</p> Signup and view all the answers

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Flashcards

Type I Hypersensitivity

An immediate and exaggerated immune response to an allergen, involving IgE antibodies, mast cells, and the release of histamine.

Type II Hypersensitivity (Cytotoxic)

A hypersensitivity reaction in which antibodies bind to antigens on cell surfaces, leading to cell lysis or damage. Examples: ABO incompatibility in blood transfusions, Rh incompatibility in newborns.

Type III Hypersensitivity (Immune Complex)

A hypersensitivity reaction triggered by immune complexes formed from antigens and antibodies. These complexes deposit in tissues, activating complement and causing inflammation. Examples: serum sickness, Arthus phenomenon.

Type IV Hypersensitivity (Cell-Mediated)

A delayed-type hypersensitivity reaction mediated by T cells, which directly attack target cells or release cytokines that cause tissue damage. Examples: contact dermatitis, allograft rejection.

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Tolerance

The ability of the immune system to distinguish self from non-self and avoid attacking the body's own tissues. This prevents autoimmune diseases.

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Autoimmunity

The immune system mistakenly attacks the body's own tissues. This happens when the body's immune system fails to recognize self-antigens and launches an immune response against them.

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Adaptive immune response

A type of immune response that involves the recognition and destruction of foreign antigens, such as those found on bacteria or viruses. This involves the production of antibodies and the activation of T cells.

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Breakdown in autotolerance

The immune system fails to distinguish between self and non-self antigens. This can lead to the production of autoantibodies, attacking the body's own tissues.

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Exposure to sequestered antigens

This occurs when the immune system encounters proteins normally hidden from the body's defenses. These hidden antigens are usually sequestered, meaning they're not exposed to the immune system during development. When released, they can trigger an immune response, leading to autoimmune disease.

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Structural modification of tissue proteins

Drugs, chemicals, or viruses can alter the structure of tissue proteins, making them appear foreign to the immune system. This leads to an immune response against these modified proteins, causing autoimmune disease.

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Autotolerance

The body's ability to not mount an immune response against its own antigens. This is a normal process that prevents the immune system from attacking the body's own cells.

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Type II cytotoxicity

A type of hypersensitivity reaction where the immune system attacks foreign antigens that are bound to the surface of cells. This is a direct attack on specific cells, leading to their destruction.

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Immune Complex-Mediated Hypersensitivity (Type III)

A type of hypersensitivity reaction where immune complexes (antigen-antibody complexes) are formed in the bloodstream and deposited in various tissues, leading to inflammation and tissue damage.

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Hypersensitivity

An exaggerated immune response against an antigen that is not inherently harmful, but can lead to various allergic reactions.

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Delayed Hypersensitivity (DTH - Type IV)

A type of hypersensitivity reaction mediated by T cells, where the immune system mounts a delayed response to a specific antigen. This occurs 48-72 hours after exposure to the antigen.

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Immediate Hypersensitivity (Type I)

A type of hypersensitivity reaction mediated by IgE antibodies. Immediate hypersensitivity is characterized by rapid onset (minutes) and involves the release of histamine and other mediators from mast cells.

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Contact Dermatitis

A delayed hypersensitivity reaction that occurs after exposure to substances like poison ivy or nickel. It involves an inflammatory response in the skin, characterized by red, itchy, and sometimes blistering patches.

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Tuberculin Test

A delayed hypersensitivity reaction that is commonly used in diagnosing tuberculosis. This test involves injecting a small amount of tuberculin under the skin. A positive reaction indicates prior exposure to the tuberculosis bacteria.

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Acquired Tolerance

A type of tolerance that is induced during life. This occurs when the immune system is exposed to an antigen over time, leading to decreased or absent immune responses. This is a more controlled induction of tolerance.

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Study Notes

Hypersensitivity Reactions and Autoimmunity

  • Hypersensitivity reactions are harmful immune responses to a harmless antigen.
  • Autoimmunity is a breakdown in tolerance where the immune system attacks its own body's cells.

Lecture Outline

  • Hypersensitivity reactions
  • Autoimmune diseases and tolerance

Lecture Learning Objectives

  • Understand Hypersensitivity reactions
  • Understand autoimmune diseases and tolerance

Immunopathogenesis

  • Immunopathogenesis is the study of the disease mechanisms of hypersensitivity reactions.

Gell and Coombs Classification of Hypersensitivity Reactions

Type Examples Mechanism
I Anaphylaxis, asthma, hay fever, eczema, food allergies IgE
II HTR caused by ABO incompatibility, HDN caused by Rh incompatibility Cytotoxic Ab
III Serum sickness, Arthus phenomenon, rheumatoid arthritis Immune complexes
IV Koch's phenomenon, allograft rejection, contact dermatitis Cell-mediated

Type I Hypersensitivity Reactions

  • Allergen triggers the production of IgE antibodies, binding to mast cells.
  • Subsequent exposure to allergen leads to mast cell degranulation and release of vasoactive amines.
  • This results in a range of symptoms, including inflammation and tissue damage.
  • The process is regulated by CD4 cells and IL-4.

IgE-mediated Allergic Reactions

  • This table describes common allergens, their routes of entry, and resulting symptoms in IgE-mediated allergic reactions.
Syndrome Allergen(s) Route(s) of entry Response
Systemic anaphylaxis Drugs, serum, venoms, peanuts IV (injection to tissue) Increased vascular permeability, edema, tracheal occlusion, circulatory collapse, and death
Wheal and flare Insect bites, Allergy testing Subcutaneous Local increase in blood flow and vascular permeability
Allergic rhinitis (hay fever) Pollens, dust-mite feces Inhaled Edema of nasal mucosa, irritation of nasal mucosa
Bronchial asthma Pollens, dust mite feces Inhaled Bronchial constriction, increased mucus production, airway inflammation
Food allergy Shellfish, Milk, Eggs, Fish, Wheat Oral Vomiting, diarrhea, pruritis, urticaria, anaphylaxis

Skin Prick Test for Allergy Diagnosis

  • Introducing a low dose allergen into skin to detect immediate hypersensitivity reactions.

Drug Hypersensitivity

  • A series of hypersensitivity reactions triggered by medication, including skin rashes, inflammation, and other symptoms.

Erythema Nodosum Lesions

  • Skin lesions due to hypersensitivity to Coccidioides immitis antigens .

Bite Reactions

  • Skin reactions, appearing as multiple linearly arranged erythematous nodules, with tense blister formation.

Hives (Urticaria)

  • Skin rashes, characterized by red, raised, itchy areas.

Type II Cytotoxic Mechanism

  • Antibodies bind to target cells, leading to their destruction by complement activation or phagocytosis.

Immune Complex-Mediated Hypersensitivity

  • Immune complexes (antigen-antibody complexes) deposit in tissues, activating complement and attracting inflammatory cells.
  • Resulting inflammation and tissue damage are characteristic of this type of hypersensitivity. This can lead to many issues.

Mechanisms of Damage in Immune Complex Hypersensitivity

  • Immune complexes are formed from antigen and antibody, aggregated platelets are involved, and complement is activated.
  • Vasoactive amines are released, microthrombi form, and enzymes are released.
  • This leads to inflammation, tissue damage, and other complications.

Immune Complex Hypersensitivity

  • Immunopathological responses due to the formation of immune complexes in tissues, resulting in various diseases.

Immunopathogenesis/ Tolerance and Autoimmunity

  • Discusses tolerance to self-antigens; when tolerance to outside antigens is required, which can cause issues like autoimmune diseases.

Definition of Tolerance

  • The body's ability to not attack its own cells, meaning it doesn't attack its own self-antigens. This has two aspects:
  • Auto-tolerance (natural tolerance of self-antigens).
  • Acquired tolerance (induced tolerance of outside antigens).

Autotolerance

  • Tolerance to self-antigens, induced early in development, mainly in utero. Failure can cause autoimmune diseases.

Acquired (Induced Tolerance)

  • Induction of tolerance to an antigen throughout life. This is important for allergy treatment, immune response to an antigen, and graft rejection.

Definition of Autoimmune Disease

  • Adaptive immune response to self-antigens, leading to the production of autoantibodies and/or self-reactive T-cells, resulting in autoimmune diseases.

Aetiology of Autoimmune Diseases (Causes)

  • Exposure to sequestered antigens:
    • Antigens not usually exposed to the immune system during development, but exposed for example by injury to these areas, will trigger an immune response
  • Structural modification of tissue proteins:
    • Certain drugs, chemicals or viruses can alter protein structures on tissues.
    • These proteins are no longer recognized by the body as self and the immune system will initiate an attack leading to autoimmune diseases.
  • Cross-reactivity:
    • Antibodies produced against one antigen can react with similar antigens on other tissues, which is known as cross-reactivity.
    • This leads to the body attacking its own tissues instead of the foreign antigen.

Genetic Predisposition to Autoimmune Disease

  • Genetic factors play a role
  • Some autoimmune diseases run in families
  • This may be linked to specific MHC antigens, which are capable of presenting self peptides to self-reactive cells.
  • Several autoimmune diseases exhibit strong associations with specific MHC proteins.

Mechanisms of Tissue Injury in Autoimmune Disease

  • Type II: Cytotoxic reactions
  • Type III: Immune-complex-mediated reactions
  • Type IV: Cell-mediated reactions

Ulcerative Colitis

  • A form of inflammatory bowel disease.

Lab Diagnosis of Autoimmune Diseases

  • Elevated serum immunoglobulins
  • Presence/detection of autoantibodies
  • Detection of immune complexes in serum and tissues
  • Level of complement in serum

Management of Autoimmune Diseases

  • Anti-inflammatory drugs
  • Immunosuppressive drugs
  • Plasmapheresis
  • Interference with cytokine network

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Lecture 10: Hypersensitivity & Autoimmunity PDF

Description

This quiz covers hypersensitivity reactions and autoimmune diseases, exploring the mechanisms and classifications involved. Gain insights into how the immune system can react harmfully to harmless antigens and the breakdown of tolerance that leads to autoimmunity.

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