Allergies

Question 1

What is an allergy?

Answer 1

disease following a response by the immune system to an otherwise innocuous antigen

Question 2

what is a hypersensitivity?

Answer 2

harmful immune responses that produce tissue damage

Question 3

What is the immun reactant in type I hypersensitivity?

Answer 3

IgE

Question 4

Describe the antigen in in type I hypersensitivity

Answer 4

Soluble

Question 5

What is the effector mechanism in in type I hypersensitivity?

Answer 5

Mast cell activation and degranulation

Question 6

What is an example of in type I hypersensitivity

Answer 6

Allergy

Asthma

Question 7

Describe the mediation of allergy by antibodies

Answer 7

IgE mediated and always occurs on secondary exposure to an allergen, so an initial exposure event has always taken place

Question 8

Describe the normal serum levels of IgE and the reason for this?

Answer 8

very low

sticks to mast cells

Question 9

When does allergy occur?

Answer 9

When IgE triggers mast cell degranulation

Question 10

Where is IgE produced?

Answer 10

produced by plasma B cells in lymph nodes or locallat sites of inflammation

Question 11

Where is IgE located?

Answer 11

in tissue, bound to mast cell surface due to high affinity of IgE receptor FceRI

Question 12

What cells fabour IgE responses>

Answer 12

CD4+ T cells of the Th2 phenotype that produce IL4 cytokines favour IgE responses

Question 13

What do CD8 cytotoxic cells produce?

Answer 13

• IFNgamma
• TNFalpha

Target cell lysis

Question 14

What do CD4 Th1 cells produce?

Answer 14

• IFNgamma
• GM-CSF
• TNFalpha

macrophage activation

Question 15

What do CD4 Th2 cells produce?

Answer 15

• IL4
• IL5

B cell activation

Question 16

What are some common sources of allergens?

Answer 16

• inhaled material
  
  • plant pollens
  • house dust mite
• injected material
  
  • venoms
  • vaccines
  • drugs
• ingested material
  
  • food
  • orally administered drugs
• contacted materials
  
  • plant lkeaves
  • industrial products from plants
  • synthetic chemicals in industrial products
  • metals

Question 17

What are the main features of inhaled allergens?

Answer 17

• protein - T cell response
• Enzymatically active
• Low dose - IL4 response = CD4 T cells
• small size
• highly soluble
• stable - survive dessication

Question 18

What is IgE thought to be cruical against?

Answer 18

host defence against parasites

Question 19

What is the major allergen in house dust mite?

Answer 19

Der p 1

Question 20

How does Der p 1 work?

Answer 20

can cleave tight junctions between epithelial cells allowing access

taken up by dendritic cells, presented to T cells, which becomes Th2 and cause B cells to secrete IgE

Question 21

What is the most important factor in determining the symptoms of an allergen?

Answer 21

location and distibrution

Question 22

What is allergic asthma?

Answer 22

• bronchial constriction
• increased secretion of fluid and mucus trapping inhaled air
• chronic inflammation may follow with the continued presence of Th2 cells, eosinophils and neutrophils

Question 23

Draw a graph showing the FEV (air expulsion capacity) in an asthmatic response

Answer 23

Question 24

What usually occurs in a skin allergy?

Answer 24

rashes

Question 25

What is wheal and flare a result of?

Answer 25

vasodilation after mast cell degranulation causing localised redness

Question 26

What happens approx. 8 hrs after a skin allergy occurs?

Answer 26

oedema at the site due to influc of lymphocytes and other leukocytes attacted by chemokines

Question 27

What do ingested allergens cause?

Answer 27

• Activation of GI Mast cells results in transepithelial fluid loss and smooth muscle contraction: diarrhea and vomiting
• If allergen enters blood stream, generalised disseminated rash, Urticaria, (hives).
• In severe cases of food allergy, eg nuts and shellfish, life threatening generalised anaphylaxis and cardiovascular collapse may occur

Question 28

What are the main chemical mediators involved in allergic response?

Answer 28

• lipids
• toxic mediators
• cytokines
• enzymes

Question 29

What is the effect of lipids in allergic response?

Answer 29

• Prostaglandins; increased vascular permeability, increased body temperature.
• Platelet activating Factor; increased adhesion between endothelium and neutrophils.
• Leukotrienes, attract and activate neutrophils, increased vasc permeability

Question 30

What is the effect of toxic mediators in allergic response?

Answer 30

• Histamine; increased vascular permeability, and promotes movement of fluid from the vasculature by constricting vascular smooth muscle.
• Heparin, inhibits coagulation

Question 31

What is the effect of cytokines in allergic response?

Answer 31

• IL-4, IL-13; amplify Th2 response
• IL-3, IL-5, GM-CSF; promote eosinophil activation and production
• TNF-alpha; pro-inflammatory, activates endothelium
• Chemokine MIP-1alpha; attracts macrophages and neutrophils

Question 32

What are the enzymes involved in allergic response?

Answer 32

• Tryptase
• Chymase
• Cathepsin G
• Carbopeptidase
• Remodel connective tissue matrix

Question 33

What are the two main types of treatment currently used for treatment of allergy?

Answer 33

densensitisation and blockade of effector pathways

Question 34

How does desensitisation and blackade work?

Answer 34

• Aim to shift response from IgE dominated to IgG dominated
• Patients injected with escalating doses of allergen, gradual shift from Th2 to Th1 T cells.
• Potential risk of inducing anaphylaxis!
• Anti-histamines, H1 receptor blocking.
• Topical or systemic corticosteroids to supress chronic inflammation in asthma and rhinitis

Question 35

What should severe anaphylaxis be treated with?

Answer 35

epinephrine (adrenaline) injection

Question 36

What is a key defence in helminth expulsion?

Answer 36

IgE