Allergies Flashcards

1
Q

Define allergy?

A
  • Disease following a response by the immune system to an otherwise innocuous antigen.
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2
Q

Define Hypersensitivity

A

Harmful immune responses that produce tissue damage

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3
Q

What are the different types of hypersensitivity reactions and the immune reactant involved?

A

Type 1 - IgE.

Type 2 - IgG.

Type 3 - IgG.

Type 4 - Th1 cells, Th2 cells and cytotoxic T lymphocytes

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4
Q

Describe how allergy is mediated

A

It is IgE mediated and always occurs on secondary exposure to an allergen. So initial exposure event has always taken place. Allergy occurs when IgE triggers Mast cell degranulation

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5
Q

Describe the production of IgE antibodies

A

They are produced by plasma B cells in lymph nodes, or locally at the site of inflammation

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6
Q

Where is IgE located?

A

Mostly in tissue bound to mast cell surface through high affinity IgE receptors

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7
Q

What type of cells favour IgE responses?

A

CD4+ T cells of the Th2 phenotype that produce IL4 cytokines. Th2 T cells also force B cells to switch the isotype of theduce Ig they secrete from IgM to IgE

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8
Q

What does CD4 Th1 cells produce and what does this cause?

A

They produce TNF alpha, interfuron gamma and GM-CSF which cause macrophage activation

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9
Q

What does CD4 Th2 cells produce and what does this cause?

A

IL4 and IL5 which causes B cell activation.

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10
Q

What doe CD8 cytotoxic T cells produce?

A

Interferon gamma and TNF alpha which target cell lysis

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11
Q

What are some common allergens?

A

Inhaled materials - Pollen and house dust mites.

Injected materials - Wasps or drugs.

Ingested materials - Food or oral drugs

Contacted materials - Plant leaves, chemicals and metals

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12
Q

Describe the function of Der p and how it triggers an immune response

A

It is a major allergen in feces of house dust mites and can cleave tight junctions between epithelial cells in the airway. Der p 1 is taken up by dendritic cells, present to T cells which then become Th2 and cause B cells to secrete IgE

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13
Q

Describe what occurs in allergic asthma?

A
  • Bronchial constriction, increased secretion of fluid and mucus, trapping inhaled air.
  • Chronic inflammation may then occur with continued presence of Th2 T cells, eosinophils and neutrophils
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14
Q

Describe what occurs with a skin allergy?

A
  • Allergens entering the skin site causes rash. Wheal and flare first appears within mins due to vasodilation after mast cell degranulation. After 8 hours more diffuse oedema at the site due to influx of lymphocytes and leukocytes.
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15
Q

Describe what occurs when you ingest an allergen?

A

It leads to two main symptoms:
- Activation of GI mast cells results in transepithelial fluid loss from smooth muscle contraction - vomiting and diarrhoea.

  • If allergens enter bloodstream then generalised disseminated rash and urticaria.
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16
Q

What are the chemical mediators of an allergic response? Name an example of each

A

Mast cells which contain a wide range of inflammatory mediators:

  • Lipids (Prostaglandins which increase vascular permeability, body temp),
  • Toxic mediators (histamine which increases vascular permeability and heparin which inhibits coagulation),
  • Cytokines (IL-4 which amplifys the Th2 response and TNF alpha which is pro-inflammatory),
  • Enzymes
17
Q

Describe the treatment of allergy?

A

There are two men types; desensitisation - Patients injected with escalating doses of allergen which results in a gradual shift from Th2 to Th1 cells (potential risk of anaphylaxis).

Blockade of effector pathways - Anti-histamines (H1 receptor blockers)

18
Q

How should you treat severe anaphylaxis?

A

Injection of adrenaline. 0.15mg for child and 0.3mg for adult

19
Q

Describe the theory’s of why the population are having for allergic reactions

A
  • Hygiene hypothesis, are we not exposed to as many infectious disease in early childhood?
  • Pollution, does it increase allergic asthma?
  • Infection control, Allergies and asthma is lower in areas of high helminth burdens. IgE is a key defence in helminth expulsion. Data suggests helminth infections induce T cells Tregs which suppress activity of Th2 cells.
20
Q

DEscribe genetic influences on allergy.

A

There are many genes that can influence allergy, not just one. Some examples are IL-4 promotor variants and IL-4 receptor variants