Allergy Flashcards
Definition of allergy
A hypersensitive disorder of the immune system
What do allergic reactions occur in response to?
Normally harmless environmental substances known as allergens
Definition of allergic reaction
An exaggerated or inappropriate immune reaction and causes damage to the host
What are some common allergic reactions?
Eczema
Allergic Rhinitis
Asthma
Food allergies
How does skin manifest with allergic reactions?
Urticaria / angioedema
How does the upper respiratory system present in allergic reactions?
Rhinitis
How does the lower respiratory system present in allergic reactions?
Asthma
How can allergic reactions present systemically?
Anaphylaxis
Pathology of allergic reaction
IgE mediated triggering of mast cells and subsequent accumulation of inflammatory cells at sites of antigen deposition
First allergen exposure - response with T cells and B cells producing IgE
IgE circulates in the blood and binds to IgE-specific receptor (mast cells and basophils)
Pathology of the acute response to an allergen
Ag+ specific IgE
Degranulation with release of histamine, cytokines, interleukins, leukotrienes, and prostaglandins from their granules causing systemic effects such as vasodilation, mucous secretion, nerve stimulation and smooth muscle contraction
When does the late phase response after allergen exposure occur?
2-4 hours
Pathology of late phase response after allergen exposure
Migration of other leukocytes such as neutrophils, lymphocytes, eosinophils and macrophages to the initial site
Risk factors for allergies
Hereditary Race Age Exposure to infectious diseases during early childhood Environmental pollution Allergen levels Dietary changes
Presentation of an allergic reaction
Flushing or rash Burning or itching of skin Hives Nausea / vomiting Abdominal cramps Diarrhoea Sneezing Nasal congestion Runny nose Swelling and tenderness of mouth Difficulty breathing
What are some common food allergens?
Peanuts
Eggs
Milk
Dairy
What is allergic rhinitis?
Allergic inflammation of the nasal airways
When does allergic rhinitis occur?
When allergen is inhaled by an individual with a sensitised immune system
Associations of allergic rhinitis
Asthma
Atopic dermatitis
Symptoms of allergic rhinitis
Immediate - sneezing - itch - nasal blockage - rhinorrhoea - weepy eyes - coughing Late - chronic obstruction - hyposmia - hyperreactivity
Two types of allergic rhinitis
Seasonal
Perrennial
What should you check for in patients diagnosed with allergic rhinitis, especially if persistent or severe?
Asthma
What is the classification system of allergic rhinitis called?
ARIA-classification
Definition of intermittent allergic rhinitis
symptoms < 4 days per week of < 4 consecutive weeks
Definition of persistent allergic rhinitis
Symptoms > 4 days / week and > 4 consecutive weeks
Definition of mild allergic rhinitis
All of
- normal sleep
- no impairment of ADLs, sport, leisure
- no impairment of work and school
- symptoms present but not troublesome
Definition of moderate - severe allergic rhinitis
One of more of
- sleep disturbance
- impairment of ADLs, sport, leisure
- impairment of school or work
- troublesome symptoms
Pathology of type I allergic reaction
Immediate hypersensivity reactions
mediated by IgE antibodies
Which bind to receptors on mast cells and basophils
When cross linked by antigens the IgE antibodies trigger the mast cells and basophils to release pharmacologically active agents that are responsible for the characteristic symptoms of anaphylaxis
Features of a type I allergic reaction
Rapid
Occurring within minutes of exposure to antigen
Late phase reaction also present with recruitment of inflammatory cells
Pathology of a type II allergic reaction
Occur when IgM or IgG antibodies bind to antigen on the surface of cells and activate the complement cascade, which cumulates in the destruction of cells
What is a type II allergic reaction?
Cytotoxic reaction
What is a type III allergic reaction?
Immune complex reaction
Pathology of type III allergic reactions
Complexes of antigen and IgM or IgG antibodies accumulate in the circulation or in the tissue and activate the complement cascade.
Granulocytes are attracted to the site of activation, and damage results from the release of lytic enzymes from their granules
How quickly does the reaction occur after exposure in a type III allergic reaction?
Hours
What is a type IV allergic reaction?
Cell mediated immunity reaction
Another name for a type IV allergic reaction
Delayed type hypersensitivity reaction
What is a type IV allergic reaction mediated by?
T lymphocytes
Pathology of type IV allergic reaction
T cells release cytokines that cause accumulation and activation of macrophages, which cause local damage
When is the onset of type IV allergic reactions?
Delayed onset - 1 - 2 days after antigen exposure
What does the skin test test?
Responses to known allergen
What is RAST?
Presence and levels of allergen specific IgE tested in the blood
What level of RAST in the blood is negative?
Level 0 = < 0.35
What level of RAST shows a very high sensitivity?
Level 6 = > 100
What tests can be done for allergies?
Skin test RAST level in blood Total serum IgE Nasal allergen challenge Nasal cytology
Treatment of allergies
Avoidance Antihistamines Glucocorticoids Epinephrine Immunotherapy
What is immunotherapy useful in?
Allergic rhinitis
Allergic asthma
Allergic conjunctivitis
Where is immunotherapy NOT used?
Food allergy
Urticaria
Atopic dermatitis
What does immunotherapy involve?
Controlled exposure to known allergens to reduce the severity of the allergy
