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Immune System > 1. Hypersensitivity Reactions > Flashcards

1. Hypersensitivity Reactions Flashcards

1
Q

What is the definition of hypersensitivity?

A

The antigen-specific immune responses that are either inappropriate or excessive and result in harm to host

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2
Q

Give examples of exogenous antigens that can cause hypersensitivity

A

Non infectious substances (innocuous)
Infectious microbes
Drugs (penicillin)

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3
Q

Give examples of intrinsic antigens that can cause hypersensitivity

A 
Infectious microbes (mimicry)
Self antigens (auto-immunity)
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4
Q

What are the broad types of hypersensitivity reactions?

A

Type I/immediate (allergy)
Type II/antibody mediated
Type III/immune complexes mediated
Type IV/cell mediated (delayed)

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5
Q

What is the sensitisation phase?

A

First encounter with the antigen. Activation of APCs and memory effector cells. A previously exposed individual to the antigen is said to be sensitised

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6
Q

What is the effector phase?

A

Pathologic reaction upon re-exposure to the same antigens and activation of the memory cells of the adaptive immunity

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7
Q

How long after exposure does type II hypersensitivity usually develop?

A

5-12 hrs

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8
Q

Which antibodies do type II hypersensitivity reactions involve?

A

IgG or IgM

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9
Q

Which antigens do type II hypersensitivity reactions target?

A

Cell bound antigens

  • exogenous: blood group antigens, Rhesus D antigens
  • endogenous: self antigens
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10
Q

What are the 2 different outcomes induced in type II hypersensitivity reactions?

A

Tissue/cell damage

Physiological change

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11
Q

Describe the mechanisms of type II hypersensitivity causing tissue/cell damage

A

Complement activation - cell lysis, neutrophil recruitment/activation, opsonisation
Antibody-dependent cell cytotoxicity

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12
Q

Give examples of the complement activation mechanism in type II hypersensitivity

A

Haemolytic disease of the newborn (HDN)

Transfusion reactions

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13
Q

Give examples of antibody-dependent cell cytotoxicity mechanism in type II hypersensitivity

A

Autoimmune haemolytic anaemia
Immune thrombocytopenic purpura
Goodpastures syndrome

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14
Q

Give 2 examples of disease caused by type II hypersensitivity (IgM)

A

Haemolytic transfusion reactions

Immune mechanism - ABO or Rhesus D antigens

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15
Q

Give an example of disease caused by type II hypersensitivity (IgG)

A

Haemolytic disease of the newborn

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16
Q

What are the mechanisms of type II hypersensitivity causing physiological change?

A 
Receptor stimulation (Graves’ disease)
Receptor blockade (myasthenia gravis)
17
Q

What are the therapeutic approaches to type II hypersensitivity causing tissue/cell damage?

A

Anti-inflammatory drugs
Plasmapheresis
Splenectomy
Intravenous immunoglobulin

18
Q

Which diseases is plasmapheresis therapy used in?

A

Myasthenia gravis
Goodpastures syndrome
Graves’ disease

19
Q

How long after initial exposure does type II hypersensitivity develop?

A

3-8 hrs

20
Q

Which immune complexes are involved in type III hypersensitivity?

A

Immune complexes between IgG or IgM and antigens

21
Q

What does type III hypersensitivity target?

A

Soluble antigens - foreign (infection), endogenous (self antigens)

22
Q

What is tissue damage caused by in type III hypersensitivity?

A

Caused by the deposition of immune complexes in host tissues

23
Q

What are the key factors that affect immune complex pathogenesis in type III hypersensitivity?

A

Complex size
Host response
Local tissue factors

24
Q

What are the immune mechanisms in type III hypersensitivity?

A
  1. Intermediate-sized immune complexes deposited in the tissue
  2. Complement activated
  3. Neutrophil chemotaxis
  4. Neutrophil adherence and degranulation
25
Q

Give examples of diseases caused by type III hypersensitivity reactions

A

Rheumatoid arthritis - develop antibodies against Fc portion of IgG
Glomerulonephritis
Systemic lupus erythematosus

26
Q

How long after initial exposure does type IV hypersensitivity develop?

A

24-72hrs

27
Q

Which cells does type IV hypersensitivity involve?

A

Lymphocytes and macrophages

28
Q

What are the subtypes of type IV hypersensitivity?

A

Contact hypersensitivity
Tuberculin hypersensitivity
Granulomatous hypersensitivity

29
Q

Which cells are present in the effector phase of type IV hypersensitivity?

A

TH1

Macrophages

30
Q

Give examples of diseases caused by type IV hypersensitivity to exogenous antigens

A

Contact hypersensitivity - epidermal reaction e.g. nickel, poison ivy, organic chemicals
Granulomatous hypersensitivity - tissue damage e.g. TB, leprosy, schistosomiasis, sarcoidosis

31
Q

Give examples of diseases caused by type IV hypersensitivity to endogenous antigens

A

Pancreatic islet cells - DM
Thyroid gland - Hashimoto’s thyroiditis
Fc portion of IgG - rheumatoid arthritis

32
Q

What is the therapy for type III and IV hypersensitivity?

A

Anti-inflammatory drugs - NSAIDs, corticosteroids, steroid-sparing agents
Monoclonal antibodies

33
Q

What are the mechanisms of type I hypersensitivity?

A

Abnormal adaptive immune response against the allergens - T helper 2 response against exposure, causes IgE production
IgE causes mast cell activation

34
Q

Name the important mast cell mediators

A

Tryptase
Histamine
IL-4, IL-13, IL-5
Leukotrienes C4, D4, E4

35
Q

What is urticaria caused by?

A

Mast cell activation within the epidermis

Mediators are histamine and leukotrienes/cytokines

36
Q

What is angioedema caused by?

A

Mast cell activation in deep dermis

Mediators are histamine and bradykinin

37
Q

What are the systemic manifestations of allergic reactions (anaphylaxis)?

A

Systemic activation of mast cells leads to:

  • hypotension
  • cardiovascular collapse
  • generalised urticaria
  • angioedema
  • breathing problems
38
Q

What is the action of IM adrenaline in anaphylactic shock?

A

Reverses peripheral vasodilation and reduces oedema and alleviates hypotension
Reverses airway obstruction/bronchospasm
Increases the force of myocardial contraction
Inhibits mast cell activation

39
Q

What is the therapy for type I hypersensitivity?

A

Oral immunotherapy - allergen desensitisation
Omalizumab - anti-IgE monoclonal antibody
Mepolizumab - anti-IL5 monoclonal antibody
Anti-histamine
Leukotriene receptor antagonists
Corticosteroids

Immune System (4 decks)

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