1. T1HS

Question 1

Explain the pathogenesis of T1HS

Answer 1

i. 1st exposure to trigger/allergen… abnormal TH2 activation… plasma cell production of antigen-specific IgE (sensitisation)
ii. 2nd exposure to antigen… IgE crosslinking on mast cells… mast cell activation and degranulation… release of histamine and chemokines
iii. increased vascular permeability, vasodilation and bronchial constriction

Question 2

name 3 examples of allergens

Answer 2

1. tree and glass pollens
2. house dust mite
3. animal dander (cats and dogs)
4. fungal spores
5. insect venom (wasp and bee stings)
6. medicines, e.g. penicllin
7. chemicals, e.g. latex
8. foods, e.g. milk, peanuts, etc.

Question 3

suggest 3 reasons why allergies are more prevalent in westernised countries than developing countries

Answer 3

1. hygiene hypo. - children exposed to animals, pets and microbes in the early post-natal period appear to be protected against allergic diseases
2. biodiversity hypo. - western lifestyle induces alteration of the symbiotic relationships with parasites and bacteria leading to DYSBIOSIS of the microbiome at mucosal surfaces (gut)
3. some influence by genetics

Question 4

describe the location of mast cells

Answer 4

1. most mucosal and epithelial tissues (GI tract, skin, resp. tract)
2. in connective tissue surrounding blood cells

Question 5

what does mast cell activation in the epidermis cause? which mediators are involved?

Answer 5

• URTICARIA
• if prolonged/chronic exposure: ATOPIC DERMATITIS and ECZEMA

mediators = histamine and leukotrienes/cytokines

Question 6

what does mast cell activation in the deep dermis cause? which mediators are involved?

Answer 6

ANGIOEDEMA (lips, eyes, tongue and upper resp. airways)

mediators = histamine and bradykinin

Question 7

what does systemic activation of mast cells cause

Answer 7

anaphylactic shock:

1. increased vascular permeability and vasodilation… hypotension and cardiovascular collapse, generalised urticaria and angioedema
2. bronchial constriction… breathing probs.

Question 8

name 3 signs and symptoms of anaphylaxis

Answer 8

1. CNS
   - lightheadedness and confusion
   - loss of consciousness
   - headache
   - anxiety
2. Respiratory
   - dyspnoea
   - wheezes or stridor
   - hoarseness
   - pain with swallowing
   - cough
3. Heart and vasculature
   - brady- or tachycardia
   - low BP
4. Skin
   - hives
   - itching
   - flushing
5. GI
   - crampy abdo pain
   - diarrhoea and vomiting
6. pelvic pain, loss of bladder control, runny nose, conjunctival swelling

Question 9

what is allergen desensitisation/immunotherapy

Answer 9

administration of increasing doses of allergen extracts over a period of yrs, given to Ps by injection or sublingual

potential mechanisms:

• CD4+ CD25 Treg cells
• shift from TH2 to TH1
• inhibitory anti-inflammatory cytokines
• allergen specific blocking IgG (instead of IgE)

Question 10

name 4 possible treatments for T1HS

Answer 10

1. anti-IgE mAb
prevention of mast cell activation:
2. anti-histamines
3. leukotriene R antagonists
4. corticosteroids