CSIM1.46 Allergic Dz 1 Flashcards
List examples of type 1 hypersensitivity reactions
Atopic type 1 reaction can include urticaria (hives), allergic rhinitis, asthma attacks, anaphylaxis, angioedema,
Describe anaphylaxis
Difficulty breathing due to swelling airways, skin weels, itchy, pain. Swollen lips and tongue. Low BP: light headedness
Happens over minutes to hours
What causes a type 1 HS reaction?
Sensitisation of the immune system to a particular antigen i.e. The allergen.
Produces allergen-specific IgE which coats Mast Cells.
On subsequent exposure, allergen binds to IgE, activating the mast cell to cause degranulation and release of contents
Contents: histamine, leukotrienes, prostaglandins and other proinflammatory cytokines.
These chemicals give rise to the symptoms of a reaction namely, vasodilation, smooth muscle spasm and leukocyte extravasation.
Describe a type 2 hypersensitivity reaction “tissue-specific” and examples
Triggered by cells or matrix-associated antigens.
Antigens cause IgG to react, activating complement and antibodies against the specific tissue-type antigen. Causing tissue destruction.
Examples of type 2 HS are goodpasture’s disease, myasthenia gravis, auto-immune haemolytic anaemia.
Describe a type 3 HS reaction and examples “non-tissue specific”
reacted to by IgG, it is triggered by immune complexes deposited in different tissue.
Immune-complexes then activate IgG and complement and phagocytes causing tissue destruction
E.g. SLE, rheumatoid arthritis, farmer’s lungs
Describe a type 4 HS reaction
T cell mediated. Triggered by antigens binding to specific T-cells, causing an immmun reaction.
Attracts macrophages, cytotoxic cells and other pro-inflammatory cells.
E.g. Contact dermatitis, tuberuclin test (mantoux test), coeliac disease.
Role of mast cells in a type 1 HS reaction
Contains granules of histamine, leukotrienes, prostaglandins.
These chemicals induce edema by increasing vascular permeability, which causes extravasation of fluid and leads to swelling.
They cause smooth muscle dilation which leads to increase in blood flow to the periphery and a decrease in blood pressure.
They cause bronchospasms which cause tightening of airways and shortness of breath.
What is atopy?
Atopy is the tendency to produce IgE in response to low doses of allergens.
What is the “allergic march”
It is the tendency for atopic symptoms to present in a person in a chronological pattern
Starting with eczema, food allergy, then rhinitis and asthma all during or before the end of adolescence.
Emergency management of anaphylaxis
Lie or sit the patient Monitor O2 and assess ABC Adrenaline IM Salbultamol nebulised Fluids IV Chlorphenamine IV Hydrocortisone IV
Why is adrenaline given in an anaphylatic shock?
Adrenaline induces vasoconstriction,
increases heart rate and contractility,
also causes bronchial smooth muscle dilation and decrease mucus production.
