Type 1 hypersensitivity reaction Flashcards
Allergy
Hypersensitivity disorder of the immune system
IgE mediated antibody response to an external antigen (allergen)
Allergic reaction
Immune system reacts abnormally to harmless substances in the environment
Allergen
Substance that causes the allergic reaction
Type 1 hypersensitivity
Immediate reaction - excessive immune response resulting in an inflammatory reaction
From mins up until 2 hours after exposure to an allergen
Cells and molecules involved
Dendritic cells - Present antigen (allergen) to T cells
B lymphocytes - recognise antigen (allergen) and produce specific IgE antibody
T lymphocytes - help B cells make IgE antibody
Mast cells - produce histamine and orchestrate the inflammatory cascade
Routes of exposure to allergen
Skin contact - latex, animal dander
Ingestion - nuts, seafood
Inhalation - dust mite, pollen
Injection - medication, bee sting
Pathophysiology of an allergic reaction
Patient exposed to allergen
Dendritic cells present allergen to T cells
B cells are activated and make IgE antibody (with the help from T cells)
Mast cells release histamine and other substances which orchestrates the inflammatory cascade
Clinical features
Urticaria (rash) Itchy Angioedema Atopy - (Asthma, Hayfever, Eczema) Allergic rhinitis Conjunctivitis Nausea, Vomiting Diarrhoea Muscle spasm - broncho constriction - airway obstruction Mucosal inflammation Decreased blood pressure
Urticaria
hives, nettle rash
Morphology: red, patchy lesions appear within 1 hour of allergen exposure, very itchy
Duration: 2-6 hours
Angioedema
Localised swelling of the subcutaneous tissue in face and neck
Not itchy
Anaphylaxis
Severe, life threatening
Rapidly developing
Increased HR, decreased BP, vasodilation
stridor, flushing, urticaria, angioedema, vomiting, diarrhoea, abdo pain
Investigations
Specific IgE (RAST)
Skin prick test - gold standard, cheap, quick, expose pt to standardised solution of allergen
Challenge test - supervised exposure to allergen
Investigation to check if someone is anaphylactic
Serum mast cell tryptase - evidence of mast cell degranulation
(increased levels suggests anaphylactic)
Management of allergic reaction
Allergen avoidance
Anti-histamines - prevent effects of mast cell activation
Corticosteroids - anti-inflammatory
Mast cell stabilisers - block mast cell activation
Management of anaphylaxis
Self injectable adrenaline
- 300 for adults
- 150 or children
