Allergy Flashcards
Define allergy
A hypersensitive disorder of the immune system
Give some common allergic reactions
Eczema, asthma, food allergies, allergic rhinitis
Define allergen
An antigen which causes the allergic reaction - usually proteins
List some common food allergens
Nuts, eggs, milk, dairy, shellfish, fish
Give some common signs of an allergic reaction
Sneezing, congestion, runny nose, difficulty breathing, itching, hives, nausea/vomiting
Describe generally the pathophysiology of an allergic reaction
IgE antibody mediated triggering of mast cells and resulting accumulation of inflammatory cells at the site of antigen deposition.
Describe the pathophysiology of allergy on first exposure to an allergen
First allergen exposure prompts a response in T cells and B cells which produce IgE. IgE circulates in the blood and binds to an IgE specific receptor on mast cells and basophils
Describe the acute response to allergen exposure
Exposure of the allergen triggers allergen specific IgE production, degranulation occurs with release of histamine, cytokines, interleukins, leukotrienes - causes vasodilation, nerve stimulation, smooth muscle contraction
Describe the late-phase response to allergen exposure
2-4 hours after exposure
Inflammatory response due to migration of other leukocytes such as neutrophils, lymphocytes, eosinophils and macrophages to the initial site
What are the risk factors for allergy?
Hereditary, race, age
Environmental influences in childhood, pollution, dietary changes
Ix for allergy?
Skin test - responses to unknown allergens - high NPV, up to 15% false positive
RAST - presence and levels of allergen-specific IgE
General Tx for allergy?
Avoidance
Pharmacotherapy
Immunotherapy
Why are a positive and a negative control important when using a skin test?
Positive control = histamine, to ensure that the patient does react to histamine. Negative control = saline, to ensure that the patient does not react to the saline and therefore every allergen.
Pharmacological Tx for allergy?
Several drugs available to prevent activation of cells and degranulation processes or to block the action of allergic mediators
Antihistamines, glucocorticoids, epinephrine, antileukotrienes
Immunotherapy for allergy?
Controlled expression to known allergens. Useful for allergic rhinitis, allergic asthma
