Allergy Flashcards
what is the definition of allergy?
An IgE mediated Type I hypersensitivity reaction
what is the definition of atopy?
A genetic tendency to produce specific IgE antibodies on exposure to common environmental antigens such as house dust mute, cats, pollen and food.
What is the definition of type I hypersensitivity?
Specific IgE attaches to the Fc receptor on mast cells. Cross linkage of IgE by the allergen leads to degranulation of mast cells
What causes degranulation of the mast cell in allergy?
The IgE cross linking activates the mast cell causing it to then degranulate/
what pre-formed mediators are released from mast cell degranulation?
histamine
tryptase
heparin
what synthesised mediators are released from degranulation of mast cells?
leukotrienes
prostaglandins
How does an allergy trigger a degranulation response?
If someone is allergic on the surface of the mast cells are highly specific IgE coated receptors.
If they eat the allergen the receptors are pulled together which triggers the degranulation
what patients can’t have the skin prick test?
Patients with extensive eczema
Patients who haven’t stopped anti histamine treatment
What is the advantages of the RAST blood test?
Many allergens can be tested from the one sample
Isn’t affected by anti-histamine medications
why is it difficult to diagnose allergies in people with atopic eczema?
The skin is inflammated which drives polyclonal IgE leading to a lot of non-specific positives/
what is the serum total IgE test?
Measures the total amount, this can be normal but then one allergen can have a high specific IgE result
why can serum tryptase be helpful?
it’s a marker of mast cell degranulation
when should serum tryptase samples be taken?
- between 15 minutes and 3 hours after the onset of anaphylaxis
- second sample at 3-6 hours
- third sample at 24-48 hours
after an allergic reaction when do serum tyrptase levels return to normal?
After 12-14 hours
what are persistently elevated baseline tryptase levels associated with?
mastocytosis
what is mastocytosis?
A mast cell clonal disease where patients have unstable mast cells so are more prone to anaphylaxis
what is a true food allergy?
there is IgE mediated degranulation of mast cells
what are common food allergens?
cows milk
protein
egg
peanuts
what is a false food allergy?
There is direct stimulation of mast cells or histamine ingestion for example scromboid fish poisoning
what is a food intolerance?
An adverse reaction to food with no histamine related symptoms
what is a food aversion?
A psychological reaction
Why can some people with a food allergy ie to apples, eat them okay when they have been cooked?
the cooking process denatures the proteins
what are pan allergens?
Cross reaction proteins for example between different plants
In egg what part is more allergenic?
the egg white
