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Respiratory Pathology and Immunology > Hypersensitivity I (IMMUNOLOGY) > Flashcards

Hypersensitivity I (IMMUNOLOGY) Flashcards

1
Q

What is hypersensitivity?

A

Usually an exaggeration of normal immune mechanisms that results in bystander damage to the self

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2
Q

What is type I hypersensitivity?

A

An IgE-mediated antibody response t an external antigen (allergen)

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3
Q

What is the hygiene hypothesis?

A

Improved sanitation and decreased incidence of infectious disease has result in a world that is too clean leasing to increased predisposition to allergic conditions during childhood

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4
Q

How does a type I hypersensitivity reaction come about?

A

Stimulation of allergen-specific T-cells by allergen-derived peptides, presented by dendritic cells ( in context of MHC molecules) results in differentiation of CD4+ T-cells into effector TH2 cytokine producing cells

TH2 cells produce IL-4, IL-5, and IL-13 which coordinated the allergic response by regulating IgE synthesis by B cells, stimulating the differentiation and egress of eosinophils at site of allergen exposure

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5
Q

What are specific features of a Type I hypersensitivity reaction?

A 
Asthma
Urticaria
Angioedema
Allergic rhinitis
Allergic conjunctivitis
Diarrhoea and vomiting
Anaphylaxis
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6
Q

What are common allergens?

A 
House dust mites
Pollen 
Animal dander
Foods
Drugs
Latex
Bee & wasp venom
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7
Q

What is angioedema?

A

Self limiting, localised swelling of subcutaneous tissues or mucous membranes
Non-pitting oedema
Often without clear demarcation
Generally not itchy unless associated with urticaria

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8
Q

What occurs with mast cells upon first exposure to an allergen?

A

Express receptors for Fc region of IgE antibody on their surface (Fc-eppsillon-R1). When they encounter with allergen, B cells produce antigen-specific IgE antibody and the allergen is cleared

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9
Q

What occurs with mast cells upon second exposure to an allergen?

A

Allergen binds to IgE-coatedmast cells and disrupts cell membrane causing degranulation and release of vasoactive mediators (histamine, tryptase) also increase cytokines and leukotrienes transcription

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10
Q

What is the role of mast cells in the inflammatory cascade?

A

Increase blood flow
Contraction of smooth muscle
Increased vascular permeability
Increased secretions mucosal surfaces

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11
Q

Which type of asthma is a type I hypersensitivity reaction?

A

Extrinsic atopic asthma

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12
Q

What occurs when an allergic reaction happens in the lung?

A

Histamine and other inflammatory mediators are released causing muscle spasms (wheeze), mucous inflammation (increased sputum production) and inflammatory cell infiltrate (sputum often yellow, associated with chronicity)

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13
Q

What are the clinical features of anaphylaxis?

A 
Itch of palms, soloed feet and genitalia
Wheeze
Flushing, urticaria
Conjuctivital infection
Rhinorrhea, angioedema
Feeling impending doom, loss of consciousness , death
Angioedema of ups and mucous membranes
laryngeal obstruction,s stridor
Hypotension, cardiac arrythmias, MI
Oral itching, vomiting, diarrhoea, abdominal pain
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14
Q

What can cause spontaneous mast cell degranulation?

A

Morphine + other opiates
Non-steroidal anti-inflammatories (e.g. aspirin)
Thyroid disease
Idiopathic
Physical urticaria (due to pressure or heat)

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15
Q

What causes Samter’s Triad (aspirin-induced asthma)?

A

Aspirin and other NSAIDs
Nasal polyps
Asthma
Salicylate sensitivity

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16
Q

What are elective investigations to discover allergies?

A

Skin prick test
Quantitate IgE to putative allergen
Challenge test

17
Q

How can an allergy be diagnosed during an acute anaphylactic episode?

A

Evidence of mast cell degranulation

Serum mast cell tryptase levels

18
Q

How does a skin prick test work?

A

Expose patient to standardised solution of allergen extract through a skin prick to the forearm

19
Q

What is a positive reaction to a skin prick test?

A

Local wheal and flare response

20
Q

What precautions must be taken before a skin prick test?

A

No anti-histamines for at least 48 hrs

21
Q

Which common aeroallergens are tested in a skin prick test?

A 
house dust mites 
Animal dander
Grass pollen
Birch pollen 
Moulds
22
Q

What are the advantages of a skin prick test?

A

Cheap
Quick
Unrivalled sensitivity for most allergens
Patient can see result

23
Q

What are the disadvantages of a skin prick test?

A

Requires experience for interpretation

Very rarely may induce anaphylaxis (1:3000)

24
Q

What does an allergen-specific IgE test measure (RAST/ELISA)?

A

Amount of IgE serum that’s directed against a specific allergen

25
Q

What sensitivity does an allergen-specific IgE test have?

A

70-75%

26
Q

Why isn’t total IgE measured to investigate allergies?

A

There are other causes of elevated IgE and significant allergic disease can occur without IgE elevation

27
Q

What is tryptase?

A

Product of mast cell degranulation

28
Q

When does tryptase reach it’s peak after allergen exposure and when does it return to baseline?

A

After 1-2 hrs

Baseline after 6 hrs

29
Q

What is diagnosing allergens & resultant reaction important for?

A

Targeted avoidance

30
Q

How can mast cell activation be blocked?

A

Mast cell stabilisers such as sodium cromoglycate - stabilise mast cell membranes

31
Q

How is sodium cromoglycate administered?

A

Topical spray when allergen exposure is predictable

32
Q

How do anti-histamines function?

A

They are H1 receptor antagonists - block biological effects of histamines

33
Q

How should anti-histamines be used?

A

Prophylactically and to control symptoms

34
Q

How to leukotriene receptor antagonists work?

A

Block effects of leukotrienes which hare synthesised by mast cells after activation

35
Q

Which anti-inflammatory can be used for allergies and how does it work?

A

Corticosteroids

Inhibits format not inflammatory mediators, e.g. platelet activation factors / prostaglandins / cytokines

36
Q

How is anaphylaxis managed?

A

Self-injectable adrenaline (EpiPen) acts on beta-2-adrenergic receptors to constrict arterial smooth muscle - increases blood pressure - limit vascular leakage
Date bronchial smooth muscle - decrease airflow obstruction

37
Q

What is immunotherapy?

A

Controlled exposure to increasing amounts of allergen via subcutaneous injections to possibly inhibit anaphylaxis

Respiratory Pathology and Immunology (7 decks)

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