Allergies Flashcards
What is an allergy?
- Exaggerated immune response to a non-microbial/ environmental antigen.
- Over production of immunoglobulin E (IgE).
- Involve cytokines IL-4,5 & 13 produced by Th2 cells, IgE, mast cells and eosinophils.
What is atopy?
Genetically determined, exaggerated IgE-mediated immune response
- Type 1 hypersensitivity disorders e.g. hay-fever, asthma
What are the types of allergic disease?
Asthma, rhinitis, urticaria & angioedema and eczema
What is asthma?
Chronic disorder of airways with variable airflow limitation.
- Recurrent episodes of wheezing, breathless, tight chest, cough.
- Inhaled allergen - most common
What is rhinitis?
Respiratory disease linked with asthma
- Nasal congestion ,itching and sneezing
What is urticaria and angioedema?
Raised, itchy nettle rash - like hives
- Triggers; food and drug allergens e.g. NSAIDs, ACEIs
What is eczema?
Local inflammation of the skin
- appears in early childhood induced by food e.g. eggs, milk
Describe anaphylaxis.
Severe allergic reaction - life threatening/ death
Systems involved; respiratory, blood, cardio and gastro
Allergen triggers; food, drugs - antibiotics, venoms latex
Describe genetic predisposition.
- Influenced by inheritance of several genes/chromosomes.
- Identification of susceptibility locus for atopy on chromosomes 5q, near site of gene cluster encoding cytokines IL-4,5,9 &13
What is the hygiene hypothesis?
Cleaner environment = less microbes
Describe the skin prick test.
- Gold standard method - drop of allergen on skin, small skin prick, skin reaction - local tissue swelling and degranulation.
- Test selection of allergens according to clinical history.
- Pt must not be taking antihistamines as it will diminish sensitivity of test - false negative.
- Controls; histamines (+ve), saline (-ve).
Describe allergen sensitisation.
Exposure to an allergen leads to IgE production which results in 2 events.
- Differentiation of Tcells to Th2
- Stimulate B cells to switch to IgE production - Th2 cells produce cytokines and provide CD40 ligand to lead antibody class switching.
What are the roles of mast cells and basophils?
Initiate acute inflammatory response
Basophils - reside in circulation
Mast cells - function as immune sentinel cells and produce cytokines.
Where are mast cells found?
In connective tissue surrounding blood vessels and mucosal surfaces.
What is the granule contents of mast cells?
Histamine
Leukotrienes
Inflammatory cytokines
Neutrophil and eosinophil attracting cytokines