Infection 9 - Allergies Flashcards
What is a hypersensitivity reaction?
Immune responses that are either inappropriate or excessive, and result in harm to the host
In which phase of a hypersensitivity response are there no clinical manifestations?
Sensitization phase (1st encounter with antigen)
What is the most common hypersensitivity reaction ‘allergies’?
Type I = IgE mediated
Which antibody mediates allergic reactions?
IgE
List some symptoms of a Type I ‘allergic’ hypersensitivity reaction:
- Urticaria
- Eczema
- Rhinitis
- Asthma
- Gastroenteritis
- Angioedema
List some common allergens which trigger a Type I hypersensitivity reaction:
- House dust mite
- Animals
- Tree/grass pollen
- Insect venom
- Medicines
- Chemicals (ie latex)
- Foods (ie milk, eggs, peanuts, seafood)
What must happen for a mast cell to degrade when triggering a type I hypersensitivity reaction?
The antigen must cross-link 2 antigen-specific IgE expressed on the mast cell
What happens if an antigen cross-links 2 antigen-specific IgE expressed on a mast cell?
Mast cell begins degradation, triggering:
- Release of Histamine and Chemokines
- Synthesis of Leukotrienes and Prostaglandins
= Increased vascular permeability, vasodilation, bronchoconstriction
What complication occurs if an allergen causes the systemic activation of Mast cells?
Anaphylaxis
- hypotension
- angioedema
- general urticaria
- breathing problems
What are the main triggers of fatal anaphylaxis?
- Stings
- Food (particularly nuts)
- Antibiotics
- Anaesthetic drugs
What is the treatment for anaphylaxis?
Intramuscular Adrenaline
How many epipens do people usually need to stop and reverse an anaphylactic shock?
2 doses
What is a wheal and flare reaction?
A skin prick test which tests for allergies.
A wheal and flare > 3mm is indicative of an allergy
What is the management of a patient with an allergy?
- Allergen avoidance
- Patient (+ parent) education
- Medic alert ID
- Drugs (ie anti-histamines, corticosteroids, epipen)
- Allergen desensitisation (if high risk of anaphylaxis)
How soon do symptoms appear after a Type I hypersensitivity reaction is triggered?
< 30 mins
How soon do symptoms appear after a Type II hypersensitivity reaction is triggered?
5 - 12 hrs
- Drug-induced haemolytic anaemia
- Granulocytopenia
- Thrombocytopenia
are all types of what kind of hypersensitivity reaction?
Type II (antibody mediated) hypersensitivity reaction
How soon do symptoms appear after a Type III hypersensitivity reaction is triggered?
3 - 8 hrs
- Systemic lupus erythematosus (SLE)
- Aspergillosis
- Rheumatoid arthritis
are all types of what kind of hypersensitivity reaction?
Type III (immune-complex mediated) hypersensitivity reaction
How soon do symptoms appear after a Type IV (cell mediated) hypersensitivity reaction is triggered?
24-48 hrs
A Tuberculin Mantoux reaction is what kind of hypersensitivity reaction?
Type IV (cell mediated) hypersensitivity reaction
Why do westernised countries have an increasing prevalence of allergic disorders?
- Small families (exposed to less antigens)
- Stable intestinal flora
- Increased antibiotic use
- Reduced helminth burden
- good sanitation education
- reduced orofaecal burden
= TH2 phenotype = IgE production
What type of T helper cells are usually produced by people in developing countries, compared to those in westernised countries? How does this affect the prevalence of allergic disorders?
Developing countries = TH1 phenotype
Westernised countries = TH2 phenotype
TH2 = IgE production = Mast cell degranulation = increased prevalence of allergic disorders in westernised countries
Define atopy:
Genetic tendency to be ‘ hyperallergenic’
