(L28) Hypersensitivity Flashcards

1
Q

What are the characteristics of type I hypersensitivity?
Timing and mechanism.

L28 S4

A

Immediate response

Caused by degranulation of mast cells and eosinophils stimulated by IgE

Induced by Th2 responses/IL-4

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2
Q

What are the mast cell mediators involved in Type I hypersensitivities?

L28 S5

A

Histamine:
-vasodilator and increased permeability

Protease:
-tissue damage

Prostaglandins
-vasodilator

Leukotrienes:
-smooth muscle contraction

Cytokines:
-inflammation/leukocyte recruitment

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3
Q

What is unique to first and subsequent exposures in type I hypersensitivities?

L28 S6-7

A

First exposure to allergen:

  • causes B cell maturation and production of plasma cells that produce IgE
  • no hypersensitivity response as allergen is likely gone before IgE is produced

Subsequent exposures to allergen:

  • circulating IgE bind allergen and bind to FcεRII (CD23)
  • degranulation occurs due to cross-linking of FcεRII
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5
Q

What are the different phases of a type I hypersensitivity response?

L28 S9

A

Immediate phase:

  • occurs within minutes
  • due to degranulation
  • vasodilation, congestion, and edema

Late phase:

  • occurs 2-24 hours later
  • due to leukocyte infiltration
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6
Q

What is allergen-SIT?

L28 S13-14

A

Administration of allergen in increasing doses to cure allergies

Functions:

  • induces T cell tolerance (Tregs)
  • increases threshold for degranulation
  • decreased IgE-mediated histamine release
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7
Q

What are the characteristics of type II hypersensitivity?

L28 S16

A

IgG/IgM interaction with cell/tissue SURFACE Ags

Classical complement activation and production of anaphylatoxins resulting in leukocyte recruitment

Opsonization of cell via IgG causing neutrophil and macrophage activation

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8
Q

What are examples of type II hypersensitivity that don’t results in cell damage but instead have other physiological responses?

L28 S18

A

Grave’s disease:

  • binding of Ab to TSH receptor in thyroid, activating them
  • results in hyperthyroidism

Myasthenia gravis:
-binding of Ab to ACh receptor in neuromuscular synapses blocking stimulation

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9
Q

What are examples of type II hypersensitivity?

L28 S23

A
  • hemolytic anemia (Rh and I antigen)
  • thrombocytopenia purpora (platelet cells)
  • Goodpasture’s syndrome (basement membrane of glomeruli
  • Grave’s disease
  • myasthenia gravis
  • Pemphigus vulagaris (desmosomes)
  • rheumatic fever (cross reaction with myocardial antigens following streptococcal infection)
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10
Q

What are the characteristics of type IV hypersensitivity?
Timing and mechanism.

L28 S27

A

Delay-type hypersensitivity (DTH) (24-48 hours)

Caused by reaction of of T cells to Ag

CD8+ mediated cell killing

CD4+ (Th1/17) and macrophage cytokine mediated inflammation leading to cell damage

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11
Q

What are the characteristics of type III hypersensitivity?

L28 S24

A

IgG/IgM interaction with cell/tissue SOLUBLE Ags

Formation of immune complexes which deposit in vessels causing complement activation and leukocyte recruitment/activation

Especially problematic in lungs and kidneys

Results in ischemia

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12
Q

What are examples of type III hypersensitivity?

L28 S25

A
  • systemic lupus erythematosus (DNA)
  • polyarteritis nodosa
  • post-streptococcal glomerulonephritis
  • serum sickness (systemic vasculitis)
  • Arthus reaction (local vasculitis)
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13
Q

What is the mechanism of reaction to poison ivy?

L28 S31

A

Pentadecacatechol from poison Ivy complexes with skin protein forming a neoantigen.

The pentadecacatechol is too small to form an immune reaction on its own (hapten)

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14
Q

What are examples of type IV hypersensitivity?

L28 S29

A
  • multiple sclerosis (myelin)
  • rheumatoid arthritis
  • Type 1 DM (pancreatic β cell Ags)
  • Crohn’s disease
  • contact sensitivity (poison ivy haptens)
  • chronic infections (ie. tuberculosis)
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16
Q

What are examples of type I hypersensitivity?

L28 S4;10–11

A
Anaphylaxis (systemic)
Asthma (local)
Acute urticaria (bug bites)
Allergic rhinitis (pollen)
Food allergies
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17
Q

What are the most common contact allergens?

L28 S32

A

Metals:

  • nickel
  • cobalt
  • chromium
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