Allergy

Question 1

Type I hypersensitivity

Answer 1

IgE mediated hypersensitivity e.g. food allergy, eczema

Question 2

Type II hypersensitivity

Answer 2

Cytotoxic, antibody dependent Hypersensitivity. It can be mediated by IgM, IgG or complement. e.g. ABO blood incompatibility

Question 3

Type III hypersensitivity

Answer 3

Immune complex disease caused by IgG. E.g. Lupus, post-streptococcal glomerulonephritis

Question 4

Type IV hypersensitivity

Answer 4

Delayed type hypersensitivity, and is cell mediated. It is antibody INdependent and is mediated by T-Cells. E.g.Mantoux/tuberculin test

Question 5

How does sensitisation occur and what are the underlying physiological mechanisms involved?

Answer 5

Exposure to allergenic protein
Antigen presenting cell ( eg dendritic cell )
Th2 Lymphocyte produces IL-4 and IL-13
IL-4 acts on B Cells
B Cells stimulated to produce large amounts of Specific IgE
IgE binds to the Fc receptor on Mast Cells and Basophils
These Mast Cells and Basophils are now sensitised

Question 6

What are the actions of histamine?

Answer 6

Endothelial Cell Separation - results in localised swelling and the typical Urticarial rash

Vasodilatation - can result in hypotension

Localised irritation - of nerve endings causes itching

Bronchoconstriction - hence causes wheezing

Question 7

describe the term anaphylaxis

Answer 7

Hypotension, Bronchoconstriction or Airway compromise in the setting of an allergic reaction

Question 8

what are the signs and symptoms of anaphylaxis

Answer 8

pallor and sweating
stridor
wheeze

Question 9

how can you test for allergy

Answer 9

Food challenge - GOLD STANDARD - risk of anaphylaxis
skin prick testing - results available in 20 mins
specific IgE test - takes blood and identifies specific antibodies to allergens.