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Immunology > Hypersensitivity Diseases > Flashcards

Hypersensitivity Diseases Flashcards

1
Q

What is the classification of hypersensitivity reactions (Gel and Coomb’s)?

A 
Type I (immediate hypersensitivity)
Type II (direct cell killing)
Type III (immune complex mediated)
Type IV (delayed type hypersensitivity)
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2
Q

Type I hypersensitivity includes…

A

allergic reactions:

-IgE-mediated antibody responses to external antigen/allergen.

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3
Q

What is the mechanism of allergic reactions?

A
  1. T cells are stimulated by allergen-derived peptides, presented by dendritic cells’ MHC class II molecules.
  2. CD4+ T cells thus differentiate into Th2 cytokine-producing cells.
  3. Th2 cells produce Il-4, Il-13 and Il-5, which upregulate IgE synthesis by B cells, as well as stimulation of eosinophil production.
  4. This reaction is useful when fighting worms / helminths.
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4
Q

What are the clinical features of Type I hypersensitivity / allergic disease?

A
  • Rapid onset (1-2 mins) following exposure
  • Asthma
  • Utricaria
  • angioedema
  • hayfever (allergic rhinitis)
  • allergic conjunctivitis
  • anaphylaxis
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5
Q

What is the role of mast cells in allergic reactions?

A
  • they express Fc receptors on their surface. These bind allergen-specific IgE when it’s produced in excess to an allergen.
  • repeated exposure to the allergen causes it to bind to the IgE on the mast cell surface, triggering the release of vasoactive mediators (histamine, heparin)
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6
Q

Features of allergic reactions in lungs?

A 
muscle spasm (bronchoconstriction)
mucosal inflammation (sputum)
infiltration by inflammatory cells (yellow sputum)
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7
Q

What Allergy diagnosis (serological) methods are there?

A
  • skin prick test
  • specific IgE measurement (ELISA)
  • measure tryptase (during an aphylactic episode)
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8
Q

What is allergic disease?

A

IgE-mediated response to an external antigen.

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9
Q

What cells are involved in allergic disease?

A 
B cells (recognise antigen)
T cells (activate B cells' IgE production)
Mast cells
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10
Q

What vasoactive substances are released from the mast cells’ granules?

A

histamine, heparin, tryptase

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11
Q

What is angioedema?

A

localised swelling of subcutaneous tissues or mucous membranes

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12
Q

What are the CPx of anaphylaxis?

A

Wheeze, bronchoconstriction
Oral itching, vomiting, diarrhoea and abdo pain
hypotension, Arrhythmias, Angioedema

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13
Q

What is the pathophysiology of Type II Hypersensitivity?

A

This is Direct cell killing, characterised by antibodies to cell surface antigens.

  • antibody binds to cell-surface antigen
  • complement gets activated, causing opsonisation and cell lysis
  • antibody-mediated phgocytosis also results
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14
Q

What are examples of Type II Hypersensitivity?

A
  • Transfusion reactions (ABO incompatibility)
  • Goodpasture’s syndrome (kidney)
  • Guillan Barre syndrome (nerves/muscles)
  • Grave’s disease (anti-TSH receptor Igs)
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15
Q

What are the management options of Type II Hypersensitivity?

A
  • Plasmapheresis (remove pathogenic antibody from plasma)

- Immunosuppression (switches off antibody production by B cells)

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16
Q

What is the pathophysiology of Type III Hypereactivity?

A

Immune complex mediated:

  • Antibody is produced against soluble antigens.
  • When antigen is in excess, antibodies form immune complexes with the antigen
  • These get trapped in small blood vessels, joints and glomeruli
17
Q

What are examples of local Type III Hypersensitivity reactions?

A

Acute hypersensitivity pneumonitis:

  1. Farmer’s lung (inhaled fungal particles).
  2. Bird fancier’s ling (avian serum proteins)
18
Q

What is the CPx of acute hypersensitivity pneumonitis?

A

Wheezing, breathlessness and malaise 4-8 hours after antigen exposure

-due to leukocyte accumulation and inflammation in the alveoli

19
Q

Give an example of a systemic Type II Hypersensitivity disease?

A

Systemic Lupus Erythematosus (SLE)

20
Q

What do the pathogenic antibodies produced in Lupus (SLE) target?

A

Cell nuclear contents, causing complement in multiple body systems.

21
Q

How is Type III Hypresensitivity diagnosed?

A

test for antigen-specific IgG antobodies

22
Q

What drug is used in Type III Hypersensitivity treatment?

A

corticosteroids

23
Q

What is the pathophysiology of Type IV hypersensitivity?

A

It is T cell mediated.

  • primed effector Th1 cells and memory T cells are first generated
  • future exposure to antigen causes activation of the primed Th1 cells, causing persistent inflammation
24
Q

What are examples of autoimmune Type IV (delayed) hypersensitivity reactions?

A

Type 1 diabetes
Psoriasis
Rheumatoid arthritis

25
Q

What are examples of non-autoimmune Type IV (delayed) hypersensitivity reactions?

A

TB
Leprosy
Sarcoidosis
Transplant rejection

26
Q

What is characterisitc of sarcoidosis?

A

Multisystem granulomas

-most common in lungs

Immunology (4 decks)

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