S2 L2 Type 1 Hypersensitivity Flashcards

1
Q

How do you decide what type of hypersensitivity reaction someone is undergoing?

A
  • The trigger
  • The timing
  • Symptoms
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2
Q

Type I hypersensitivity is known as an allergy (IgE). What are the characteristics of this reaction and what are the different types of reaction?

A

- Antigen: environmental non infectious antigens (allergen)

  • Immediate reaction <30mins

- Local reaction: ingested or inhaled allergen

- Systemic reaction: insect sting or IV administration (bad)

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3
Q

What are some examples of allergens?

A

People with latex allergy often allergic to vegetable and fruit like potato and kiwi. Due to cross reactive allergens. Called oral allergy syndrome

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4
Q

What are the mechanisms that cause damage in a type I hypersensitivity reaction?

A

- Abnormal adaptive immune response against the allergens: TH2 response, IgE production

- Mast cell activation: sensitised individuals

  • Allergic disorders depend on mast cell location
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5
Q

Why do people in Westernised countries have more allergies than those in developing countries?

A

- TH1 response in developing countries forming IgG due to all of their exposures

  • TH2 respose forming IgE in Westernised world

- DIFFERENT LIFESTYLES

  • Also genetics affect allergies as well as environment
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6
Q

What is the hygeine hypothesis?

A
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7
Q

What are the two most notable factors associated with developed countries to explain the high incidence of allergies?

A

- Reduced infectious burden: animals, pets and microbes

- Microbial dysbiosis: alteration of the symbiotic relationships with parasites and bacteria

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8
Q

What is dysbiosis?

A

- Composition and functional alterations of the microbiome

  • Often occurs due to Western lifestyle, e.g from junk food, stress, c-sections, urban living, and increases risk to immune diseases and other things (see image)
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9
Q

Where are the strategic locations of mast cells?

A
  • Most mucosal and epithelial tissues - GI tract, skin, respiratory epithelium

- Connective tissue (surrounding blood cells)

  • Important role in parasitic infections and inflammation
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10
Q

What are some important mast cell mediators that are involved in an allergic reaction and what are their biological effects?

A
  • Tryptase
  • Leukotrienes C4, D4, E4
  • Platelet activating factor
  • Histamine
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11
Q

What is the immune mechanism of an allergic reaction?

A
  • 1st allergen exposure TH2 response and IgE bind to FCERI receptor on mast cell sensitising them
  • 2nd allergen exposure cross-linking of antigen specific IgE causing mast cell degranulation and release of mediators like histamines and leukotrienes that cause changes like vasodilation and increased vascular permeability
  • Location of exposure determines allergic reaction response
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12
Q

Urticaria is a skin manifestation of allergic reactions. How is it caused?

A
  • Mast cell activation within the epidermis causing itchy rash

- Mediators: histamine and leukotrienes/cytokines

  • If chronic exposure then atopic dermatitis or eczema
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13
Q

Angioedema is a facial manifestation of allergic reactions. How is it caused?

A
  • Mast cell activation in the deep dermis so non itchy

- Mediators = histamine and bradykinin

  • Occurs in lip, eyes, tongue and upper respiratory tracts which can be dangerous!!!!
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14
Q

What is anaphylaxis caused by and what are some manifestations of this pathological process?

A
  • Systemic activation of mast cells
  • Hypotension
  • CVS collapse
  • Generalised urticaria
  • Angiooedema
  • Breathing problems so stridor and wheezing
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15
Q

What is the definition of anaphylaxis and what are some of the signs and symptoms?

A

Acute onset rapidly progressive allergic reaction involving skin features and at least one other organ system (e.g CVS, GI, Lungs)

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16
Q

How do we treat anaphylactic shock and what is the mechanism of action for this therapy?

A

- IM epinephrine (adrenaline)

  • Acts on mainly A1 and B2 receptors to reverse peripheral dilation and bronchospasm and increase the force of myocardial contraction
  • Do not delay treatment, monitor pulse, b.p, oxygen, ECG
17
Q

What is needed for epipens to be effective in anaphylaxis?

A
  • IM over SC administration
  • Proper technique
  • May need multiple doses
18
Q

Why may someone be stung by a bee and have a local reaction and then five years later be stung by a bee and go into anaphylaxis?

A

Not initially sensitised to the allergen

19
Q

What are some forms of therapy for mast cell activation and abnormal adaptive immune response in type I hypersensitivity reactions?

A
  • Oral immunotherapy
  • Anti-IgE
20
Q

What is allergen desensitisation and how does it work?

A
  • Administration of increasing doses of allergen extracts over a period of years either by injection or sublingual. 90% effective in those with wasp and bee venom anaphylaxis
  • Mechanism unknown but theories
21
Q

Complete the following table.

A
22
Q

What type of hypersensitivity reaction is myasthenia gravis and how can people die from an exacerbation of this disease?

A

- Type II due to autoantibodies against AchR

  • Can go into respiratory arrest due to tiring of the diaphragm as not enough depolarisation occuring at neuromuscular junction for an action potential
  • Send to ITU and intubate
23
Q

How would you treat myasthenia gravis and what are the side effects of this treatment?

A
  • Plasmapheresis for acute exacerbation
  • Pyridostigmine (AchE inhibitor) which causes an increase in Ach concentration in the synaptic cleft so more likely to depolarise the end plate

- SLUDGE: salivation, lacrimation, vomiting, diarrhoea, cough, sweating, muscle twitching/cramps

24
Q

What are some examples of diseases cause by type II hypersensitivity reactions associated with changes in receptor function?

A
  • Myasthenia Gravis
  • Grave’s disease
  • Anti-GBM syndrome