allergy

Question 1

atopy?

Answer 1

Specific IgE very important in helminth infestations
Atopy = production of specific IgE against common environmental allergens
>30% of the population atopic by this definition
50% atopic by 2030 (WHO estimates)
>20% of the population have symptoms of 1 or more allergic disorder (rhinitis, asthma, eczema, food)
Allergen processed normally, TH2  IL-4,5  IgE produced + development of mast cells & eosinophils
Mast cells & eosinophils make IL-3,4,5, GM-CSF

Question 2

asthma, intrinsic and extinsic?

Answer 2

Affects 20% children, 10-15% adults
Extrinsic: triggered by certain allergens
Intrinsic: no allergens identifiable

Question 3

hgow to diagnose asthma?

Answer 3

Any allergens responsible can be identified by skin tests or RAST/FEIA so as to try and decrease exposure

Extrinsic asthma has biphasic response - immediate phase within 30min (due to histamine + other mast cell pre-formed mediators) and delayed phase 6-8hr later due to later action of further mediators after infiltration by lymphocytes and granulocytes
Essential histological feature is inflammation
Rx: inh/po/iv -2 agonists, steroids, theophyllines

Question 4

anaphylaxis, non ige?>

Answer 4

Causes of non-IgE-mediated anaphylactic reactions:
blood and blood products (via C3a, C5a)
opiates, aspirin, NSAID, X-ray contrast media by direct action on mast cells
Idiopathic (ie cause unknown)

Question 5

desensitisation therapy?

Answer 5

Associated with inhibition of CD4 T-cell recruitment and decrease eosinophil activation in upper airway biopsies
Clinical response correlates with marked increase in no of cells expressing mRNA for IFNgamma on biopsy
? treatment alters TH1 -> TH2 balance in favour of TH1
The increase IFN gamma expression is associated with increaseM φ activation and increase MHC class II expression
The increase IgG4 concentrations may be an epiphenomenon indicating the fundamental shift in TH1/TH2 balance
? treatment induces CD4+25+ regulatory T-cells

Question 6

eczema?

Answer 6

Often 2o skin infection eg with Staph aureus
[IgE] , RAST + skin prick test pos - ie atopic
Expansion of IL-4,5,13-secreting TH2-like cells in peripheral blood and skin
Chronic macrophage activation +  secretion of GM-CSF, PGE2
Uncertain relationship with food precipitants, allergy