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Principles > Immunology: allergic disease and hypersensitivity > Flashcards

Immunology: allergic disease and hypersensitivity Flashcards

1
Q

What is the definition of a hypersensitivity reaction?

A

Immune response that results in bystander damage to the self

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2
Q

What is type 1 hypersensitivity?

A

Immediate hypersensitivity i.e. allergy

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3
Q

What is type 2 hypersensitivity?

A

Antibody mediated hypersensitivity

Direct cell killing

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4
Q

What is type 3 hypersensitivity?

A

Immune complex mediated (i.e. antibody-antigen complex) hypersensitivity

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5
Q

What is type 4 hypersensitivity?

A

Delayed type hypersensitivity i.e. T cell mediated

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6
Q

What is the definition of allergy?

A

IgE-mediated antibody response to external antigen

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7
Q

What are some of the environmental risk factors for developing allergy?

A

Westernised culture
Low exposure to bacteria - “hygiene hypothesis”
High antibiotic use

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8
Q

What are the immune cells involved in the allergic response and what do they do?

A

B lymphocytes: recognise antigen and produce antigen-specific IgE antibody
T lymphocytes: provide help for B lymphocytes to make IgE antibody
Mast cells: release vasoactive substances

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9
Q

What do B cells do in response to allergen?

A

Produce antigen specific IgE antibodies to clear antigen

Excess IgE antibodies bind to Fc receptors on mast cells

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10
Q

What happens to mast cells after re-encounter with allergen?

A

Allergen binds to IgE-coated mast cells and causes degranulation, releasing vasoactive mediators, histamine, tryptase and increases transcription of leukotrienes and cytokines

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11
Q

What is extrinsic asthma?

A

IgE mediated response to external allergen e.g. dust mite, pollen etc

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12
Q

What is intrinsic asthma?

A

“Non-allergic” asthma i.e. genetic

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13
Q

What effect does release of histamines from mast cells have on the lungs?

A

Bronchospasm
Inflammatory cell infiltration
Mucosal inflammation

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14
Q

What is urticaria?

A

Hives

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15
Q

What are some non-allergic i.e. non-IgE mediated causes of mast cell degranulation?

A

Urticaria in response to pressure or heat
Morphine and other opiates
Aspirin and non-steroidal anti-inflammatories
Thyroid disease
Idiopathic

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16
Q

What is aspirin asthma?

A

Onset of wheeze 0.5-3 hours after ingestion of aspirin or other classical NSAIDS (particularly diclofenac, ibuprofen

17
Q

What is Samter’s triad?

A

Asthma, nasal polyps and salicylate sensitivity

This is on the severe end of the scale of asthma sensitivity

18
Q

What are some of the advantages of skin prick testing?

A

Cheap
Quick (15 minutes)
Unrivalled sensitivity for the majority of allergens, particularly aeroallergens

19
Q

What is an IgE specific/RAST test used for?

A

To measure amount of IgE in serum directed against specific allergen
Sensitivity and specificity about 70 to 75% compared with skin prick tests

20
Q

How can complement increase vascular permeability?

A

Fragments of complement proteins - anaphylotoxins - released after activation increase permeability of blood vessels
This is to increase traffic of cells to inflammation

21
Q

Give a clinical example of type 2 hypersensitivity.

A

Blood transfusion reactions

22
Q

What happens in blood transfusion/ABO reactions?

A

Anti-blood group antibodies bind to surface of circulating donor erythrocytes and form antigen-antibody complexes
This activates complement which stimulates phagocytosis

23
Q

What is the clinical presentation of Immediate Haemolytic Transfusion Reaction?

A 
Overwhelming systemic inflammatory response:
Pyrexia and rigors
Tachycardia/tachypnoea 
Hypotension/dizziness
Headaches/chest or lumbar pain
May be fatal
24
Q

What are the two main forms of management of type 2 hypersensitivity reactions?

A

Immunosuppression

Plasmapheresis

25
Q

What is plasmapheresis?

A

Patient blood removed via cell separator
Cellular constituents replaced
Plasma replaced by plasma from someone else (FFP) or pooled immunoglobulin - approx. 50% plasma removed each time

26
Q

What is acute hypersensitivity pneumonitis?

A

Immune complexes deposited in the walls of alveoli and bronchioles in a type 3 hypersensitivity reaction e.g. bird fanciers lung

27
Q

Give an example of a systemic type 3 hypersensitivity reaction?

A

Systemic lupus erythematosus (SLE)

Antibodies produced against contents of cell nuclei

28
Q

What are some of the immune suppressant effects of corticosteroids?

A

Decreased release of proteolytic enzymes
Decreased traffic of phagocytes to inflamed tissue
Decreased phagocytosis
Decrease number of circulating lymphocytes
Inhibit antigen-induced Tcell proliferation
Decreased antibody production by plasma cells

Principles (8 decks)

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