What is hypersensitivity?
A state of altered reactivity in which the body reacts with an exaggerated immune response to a foreign agent
What is an allergen?
An antigen that causes allergy
What is type 1 hypersensitivity?
An allergy
Is intolerance different to allergy?
yes as there is no immunological reaction
Why is type 1 hypersensitivity sometimes called ‘immediate hypersensitivity’?
As it occurs rapidly in response to an allergen
What is type 1 hypersensitivity mediated by?
IgE
What is meant by the term ‘atopy’?
When an individual has a genetic predisposition for allergy
Type 1 hypersensitivity can lead to anaphylaxis. What is this?
An acute, serious allergic response
What are examples of inhaled materials that can cause an allergic reaction?
- Plant pollens
- Dander off of animals
What are examples of injected materials that can case an allergic reaction?
- Insect venoms
- Drugs
What are examples of ingested materials that can cause an allergic reaction?
- Food
- Orally administered drugs
What are examples of contacted materials that can cause an allergic reaction?
- Plant leaves
- Metals
What are haptens?
- Small molecules, which when combined with a larger molecule such as a carrier protein, can elicit the production of antibodies that can elicit an immune response
- Some drugs can act as haptens and induce antibody-mediated allergic reactions
What does IgE do?
- IgE producing B cells are activated during sensitisation (first exposure)
- IgE binds to Fc receptor on mast cells or CD63 on basophils
- IgE recognises allergen and next exposure binds rapidly causes immediate degranulation (elicitation)
What are examples of cutaneous (skin) atopy - wheal & flare?
- Urticaria (itchy rash)
- Allergic rhinitis (hay fever)
- Atopic dermatitis (allergic eczema)
- Asthma (lower respiratory tract)
- Food allergies (i.e. proven immunological response - not intolerance)
What is systemic anaphylaxis?
- Anaphylactic shock (mast cells degranulate all over the body)
- Three potential fatal reactions:
- Laryngeal oedema - suffocation
- Bronchiole constriction - Suffocation
- Peripheral oedema - Fluid loss from blood vessels causes hypotension (abnormally low blood pressure) and heart attack
What 4 tests can you use for type 1 allergy testing?
- Skin prick test
- Blood test
- Patch test
- Food challenge
Explain the procedure for a type 1 allergy skin prick test?
- First test to be done when looking for an allergen
- Results within about 20 minutes
- Skin pricked with a tiny amount of the suspected allergen
- Skin around the prick will become itchy, red and a wheal will appear
What is a type 1 allergy blood test?
- Specific IgE test
- Measures blood IgE antibody levels in response to allergen
What is a type 1 allergy patch test?
- tests if skin reaction due to contact with specific allergen
- Small amount of allergen added to metal discs taped to your skin for 20 mins and reaction monitored
What is a type 1 allergy food challenge?
- Diagnose food allergy
- Subject given gradually increasing amounts of the suspected food to which they are allergic and their reaction monitored
- Can only test one food at each appointment
- Has to be conducted in an ITU setting (danger to patient)
What are the possible treatments of a type 1 allergy?
- Avoid allergen (reaction can get worse with exposure)
- Drugs
- Immunological treatment
What drugs can be used to treat type 1 allergies?
- Anti-histamines - compete with histamine for receptors
- Hydrocortisone - block histamine synthesis
- Cromoglycate - Stabilises mast cells - stops histamine release
- Epinephrine - best immediate treatment for anaphylactic shock
- Reverses effects of granules
- Quick action but short duration
What is immunological treatment - hypo-sensitisation?
- repeat injections of allergen
- May work by shifting from IgE to IgG production
