Hypersensitivity

Question 1

What are the Gell-Coombs classification of hypersensitivity reactions ?

Answer 1

1. Anaphylactic/Atopic
2. Antibody-dependent cytotoxic
3. immune complex-mediated
4. T-cell mediated/Delayed

Question 2

Describe Allergy - Type 1 hypersensitivity

Answer 2

• immune mediated response to usually innocuous environmental antigens
• involves prior exposure to antigen resulting in sensitisation of individuals

Question 3

Describe Atopy - type 1 hypersensitivity

Answer 3

• susceptible to immediate HS mediated by IgE
• affects parts of the body not In direct contact with allergen
• used to describe allergic rhinitis, asthma & eczema

Question 4

Describe Type 1 - IgE mediated hypersensitivity

Answer 4

• allergens induce humour response
• generation of antibody-secreting plasma & memory cells
• plasma secrete IgE antibodies
• IgE antibodies bind to high affinity Fc£RI receptors on the surface of mast cells & basophils

Question 5

What does exposure to allergens cross-links IgEs on sensitised mast cells/basophils cause ?

Answer 5

degranulation & release of histamine and other mediators

Question 6

What are some examples of Type I Mast derived mediators ?

Answer 6

• histamine/serotonin
• PAF
• leukotrienes
• IL-4, IL-5

Question 7

Describe Allergic Rhinitis

Answer 7

• hay fever
• type I atopic allergy
• airborne allergens which diffuse across the conjunctivae & nasal mucosa
• allergic inflammation = congestion, itchy, runny eyes & nose

Question 8

Describe Atopic Dermatitis

Answer 8

• example - latex allergy
• inflammatory disease of the skin, itching, redness of eyes, nasal symptoms

Question 9

Define Urticaria

Answer 9

hives

Question 10

Describe Skin Prick testing

Answer 10

Immediate Response
- increased vascular permeability
- local edema
- itching

Late reactions (5-24hrs)
- inflammatory cell infiltrate
- Eosins, neutrophils & T cells

Question 11

Describe Type 2 Rxns

Answer 11

• activation of the complement cascade & production of the anaphylotoxin C5a & membrane attack complex
• recruitment of PMNs & subsequent tissue injury due to release of hydrolytic neutrophil enzymes after autolysis
• NK cell-mediated lysis by antibody-dependent cellular cytotoxicity