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Microbiology and immunology > Hypersensitivity > Flashcards

Hypersensitivity Flashcards

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1
Q

What is hypersensitivity?

A

Excessive or inappropriate immune response that results in a disease

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2
Q

What are the possible causes of hypersensitivity reactions?

A
  • Inappropriate immune response against host tissue (autoimmunity)
  • Inappropriate immune response against commensal microbes or inert environmental antigens (e.g. food)
  • Excessive or inappropriate response to pathogenic microbes resulting in extensive tissue destruction
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3
Q

How are hypersensitivity reactions classified?

A
  • The type of immune response (antibody- v. cell-mediated)
  • Mechanism of tissue injury
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4
Q

What types of hypersensitivity reactions are antibody mediated?

A
  • Type I
  • Type II
  • Type III
  • Type V
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5
Q

What is the pathogenic immune mediator in type I (immediate) hypersensitivity?

A

IgE

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6
Q

What is the mechanism of tissue injury in type I (immediate) hypersensitivity?

A

Mast cells and their mediators:

  • Vasoactive amines (chiefly histamine): increased vascular permeability, contraction of intestinal, bronchial, and arterial smooth muscle
  • Leukotrienes and prostaglandins: bronchoconstriction, increased vascular permeability, mucus production
  • Cytokines (IL-4, IL-5, and IL-13): recruitment and activation of inflammatory cells
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7
Q

What are examples of type I (immediate) hypersensitivity diseases?

A
  • Allergic reactions
  • Anaphylaxis (systemic allergic reaction)
  • Asthma
  • Eczema
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8
Q

What are examples of allergens?

A
  • Dust mites
  • Peanuts
  • Dyes
  • Creams
  • Fragrances in skin care products
  • Eggs
  • Pollen
  • Spores
  • Drugs
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9
Q

What is the etiology of allergy?

A

Occurs in genetically predisposed (atopic) individuals

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10
Q

What are diseases caused by allergy?

A
  • Allergic rhino-conjunctivits (hay fever): due to respiratory exposure to the allergen
  • Asthma: due to respiratory exposure
  • Food allergy: due to GI exposure
  • Atopic dermatitis (eczema): due to skin exposure
  • Anaphylaxis: due to presence of the allergen in the blood
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11
Q

How are allergic reactions managed?

A
  • Identification of the causative allergen and its avoidance
  • Anti-inflammatory agents and antihistamines to treat symptoms
  • Administration of epinephrine (EpiPen) in anaphylaxis
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12
Q

How are allergies diagnosed?

A
  • Very high levels of serum IgE
  • Skin testing to specific allergens
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13
Q

What is the pathogenic immune mediator in type II hypersensitivity?

A

IgM and IgG against antigens bound to cells or tissues

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14
Q

What is the mechanism of tissue injury in type II hypersensitivity?

A
  • Phagocytosis
  • Antibody-dependent cell mediated cytotoxicity (ADCC)
  • Receptor blocking
  • Complement-mediated lysis
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15
Q

What are examples of type II hypersensitivity diseases?

A
  • ABO incompatibility
  • Rh incompatibility
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16
Q

What is a complication of ABO incompatibility in blood transfusions or pregnancy?

A

Hemolysis and subsequent thrombosis

17
Q

What is the pathogenic immune mediator in type V hypersensitivity?

A

Stimulating antibodies against antigens bound to cells or tissues

18
Q

What is the mechanism of tissue injury in type V hypersensitivity?

A

Overactivity of the target organ

19
Q

What are examples of type V hypersensitivity diseases?

A

Grave’s disease

20
Q

How does type V hypersensitivity differ from type II?

A
  • In type II, the reaction leads to direct tissue damage
  • In type V, the reaction leads to overactivity of the target organ (e.g. the thyroid gland in Grave’s disease)
21
Q

What is the pathogenic immune mediator in type III hypersensitivity?

A

Circulating immune complexes of antigens and IgM or IgG, due to failure to clear immune complexes

22
Q

What is the mechanism of tissue injury in type III hypersensitivity?

A

Ag–Ab complexes activate the complement and Fc receptors, resulting in activation and recruitment of leukocytes

23
Q

What are examples of type III hypersensitivity diseases?

A
  • SLE
  • Rheumatoid arthritis
24
Q

What is the pathogenic immune mediator in type IV hypersensitivity?

A

CD4+ T cells or CD8+ CTLs—an exaggerated interaction between the antigen and normal T cell-mediated responses

25
Q

What is the mechanism of tissue injury in type IV hypersensitivity?

A
  • Macrophage activation (M1) resulting in cytokine-mediated inflammation
  • Direct cell killing by CTLs
26
Q

What are examples of type IV hypersensitivity diseases?

A

Tuberculosis

Microbiology and immunology (33 decks)

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