Allergy

Question 1

Which conditions are atopic? Which are not?

Answer 1

Atopy is an increased propensity to develop IgE mediated reactions to common environmental allergens
Atopic consitions:
- allergic rhinitis
- atopic asthma
- atopic dermatitis
- True food allergy

Not atopic:

• Beesting allergy
• Drug allergy
• Chronic urticaria

Question 2

Which cells and cytokines dominate the atopic response?

Answer 2

Th2 cells
IL-4 acts on naive T cells to create more Th2 cells, and B cells to promote IgE class switching
IL-13 acts on B cells to promote IgE class switching
IL-5 attracts eosinophils

Question 3

Which factors are protective for allergy (favour the Th1 phenoytpe), which factors are not (favouring Th2 phenotype)?

Answer 3

Protective:
- older siblings
- early exposure to day care
- TB, measles or Hep A infection
- rural environment
Risk factors:
- widespread use of antibiotics
- western lifestyle
- urban environment
- diet
- sensitisation to house mites and cockroaches
(also increased autoimmunity in this group)

Question 4

What conditions cause elevated IgE?

Answer 4

Atopic dermatitis +++ (greater than hay fever, rhinitis and asthma which can have levels in the normal range)
Allergic bronchopulmonary aspergillosus (level correlates to disease activity)
parasitic infection
lymphoma esp Hodgkins
Wiskott-Aldrich
Hyper IgE syndrome
IgE myeloma

Question 5

What are the steps in development of an atopic response?

Answer 5

Environmental antigen processing and presentation by an APC to a Th2 cell
Release of IL-4 and IL-13 results in Th2 cell cloncal proliferation and induction of isotpye switching of the B cell
Fc receptors on Mast cell recognise antibody attached to environmental antigen
Intracellular increase in calcium and cytokines induce the mast cell to release inflammatory mediators

Question 6

What is the pattern of reactivity following an allergen challenge (early–>late)

Answer 6

Skin-->nose-->airway
Early response (immediate) caused by vasoactive mediators from mast cells (leukotriene responsive, not antihistamine responsive, steroid resistant)
Late response (2-3 hours) caused by influx of leukocytes, especially eosinophils (cellular reaction), steroid responsive