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Immunology > Type I hypersensitivity > Flashcards

Type I hypersensitivity Flashcards

1
Q

What are the important pieces of information to obtain from someone who has had an allergic reaction?

A
  • Trigger
  • Timing
  • Symptoms
  • Therapy
  • Outcome
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2
Q

Why would someone not experience an allergic reaction when they are exposed to the allergen for the first time?

A
  • Only become sensitized after the first exposure
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3
Q

Outline type I hypersensitivity

A
  • Allergy
  • Immunological basis for different diseases
  • Immediate reaction <30 minutes
  • Antigens (allergens) that are environmental and non-infectious
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4
Q

What causes a local type I hypersensitivity reaction?

A
  • Ingested or inhaled allergen
  • E.g. eczema, hayfever
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5
Q

What causes a systemic type I hypersensitivity reaction?

A
  • Insect sting
  • IV administration
  • Ingestion
  • Allergen directly in bloodstream
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6
Q

Give some examples of allergens that cause type I hypersensitivity reactions

A
  • Seasonal exposure
  • Perennial exposure
  • Accidental exposure
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7
Q

What are some allergens that one may be exposed to seasonally?

A
  • Tree and grass pollens
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8
Q

What are some allergens that one may be exposed to perennially?

A
  • House dust mite
  • Animal dander
  • Fungal spores
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9
Q

What are some allergens that one may be exposed to accidentally?

A
  • Insect venom
  • Medicines (e.g. penicillin)
  • Chemicals such as latex
  • Foods: peanuts, milk, nuts, shellfish etc.
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10
Q

What are the mechanisms of type I hypersensitivity reactions?

A
  • Abnormal adaptive immune response against an allergen (harmless substance)
  • T helper 2 response
  • IgE production
  • Mast cell activation in sensitised individuals
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11
Q

Outline the hygiene hypothesis

A
  • Children exposed to animals, pets and microbes in the early post natal period appear to be protected against certain allergic diseases
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12
Q

Outline the biodiversity hypothesis

A
  • Western lifestyle induces alteration of the symbiotic relationships with parasites and bacteria leading to dysbiosis of the microbiome at mucosal surfaces
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13
Q

Outline the origin of mast cells

A
  • Produced by bone marrow but only mature in tissue
  • Once matured, mast cells express a receptor that binds IgE
  • Also express a stem cell receptor important for differentiation and maturation
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14
Q

Where are mast cells located in the body?

A
  • Most mucosal and epithelial tissues
  • E.g. GI tract, skin, respiratory epithelium
  • In connective tissue surrounding blood cells
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15
Q

What are the functions of mast cells?

A
  • Recruit and activate effector cells
  • Direct antimicrobial effects
  • Physiological tissue remodelling
  • Angiogenesis regulation
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16
Q

Give some examples of mast cell mediators

A
  • Tryptase (enzyme)
  • Histamine
  • Leukotrienes
  • Platelet activating factor
17
Q

What are the biological effects of tryptase?

A
  • Remodel connective tissue matrix
18
Q

What are the biological effects of histamines?

A
  • Toxic to parasites
  • Increase vascular permeability
  • Cause smooth muscle cell contraction
19
Q

What are the biological effects of leukotrienes C4, D4, E4?

A
  • Cause smooth muscle contraction
  • Increase vascular permeability
  • Stimulate mucus secretion
20
Q

What are the biological effects of platelet-activating factor?

A
  • Attracts leukocytes
  • Amplifies production of lipid mediators
  • Activates neutrophils, eosinophils, and platelets
21
Q

What is the immune mechanism of the first allergen exposure?

A
  • Direct activation of mast cells
  • Leads to production of allergen specific IgE
22
Q

What is the immune mechanism of the second allergen exposure?

A
  • Allergen cross-links form
  • Allergen binds to 2 different IgEs at cell surface of mast cells
  • This activates mast cells and causes degranulation
23
Q

What are some skin manifestations of allergic reaction?

A
  • Urticaria
  • Caused by mast cell activation within the epidermis
  • Mediators are histamine and leukotrienes/cytokines
24
Q

What are the facial manifestations of allergic reactions?

A
  • Angioedema of the lips, eyes, tongue and upper respiratory airways
  • Caused by mast cell activation in the deep dermis
  • Mediated by histamine and bradykinin
25
Q

What are the systemic manifestations of allergic reaction?

A
  • Anaphylaxis
  • Systemic activation of mast cells
  • Hypotension
  • Cardiovascular collapse
  • Generalised urticaria
  • Angioedema
  • Breathing problems
26
Q

What are some of the signs and symptoms of anaphylaxis?

A
  • Swelling of lips, tongue and throat
  • Fast or slow heart rate
  • Low BP
  • Shortness of breath
  • Wheezes or stridor
  • Pain on swallowing
  • Crampy abdominal pain
  • D and V
  • Loss of consciousness
  • Confusion
27
Q

How do we treat anaphylactic shock?

A
  • IM adrenaline
28
Q

How does adrenaline treat anaphylactic shock?

A
  • Reverses peripheral vasodilation and reduces oedema
  • Alleviates hypotension
  • Reverses airway obstruction/bronchospasm
  • Increases force of myocardial contraction
  • Inhibits mast cell activation
29
Q

What are some key points about adrenaline therapy?

A
  • Multiple doses may be required
  • Ensure that epipen is used properly
30
Q

What therapy is used to treat type I hypersensitivity reactions?

A
  • Allergen desensitization (oral immunotherapy) e.g. Omalizumab and Mepolizumab
  • Antihistamines
  • Leukotriene receptor antagonists
  • Corticosteroids
31
Q

Define allergen desensitization

A
  • It involves the administration of increasing doses of allergen extracts over a period of years, given to patients by injection or drops/tablets under the tongue
  • Effective in patients with bee and wasp venom anaphylaxis
32
Q

What are the potential mechanisms of allergen desensitization?

A
  • CD4 and CD25 regulatory cells
  • Shift from TH2 to TH1
  • Inhibitory anti-inflammatory cytokines
  • Allergen specific blocking IgG

Immunology (3 decks)

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