Hypersensitivity Flashcards
What antibody is involved in type 1 hypersensitivity?
IgE
What is meant by atopy?
Atopy = allergy
Give examples of allergies
• Anaphylaxis • Angioedema • Urticaria • Rhinitis • Asthma • Dermatitis, eczema
What are the symptoms of anaphylaxis?
Hypotension, angioedema, airway obstruction
What is angioedema?
Short lived, non-itchy oedema of the subcutaneous tissues occurs. Some forms, such as lip swelling, may be manifestations of food allergy.
Describe the role of degranulating cells.
Mast cells are resident in many tissues.
Eosinophils migrate to tissues where type I hypersensitivity reaction is.
Mast cells initiate allergic symptoms after allergen and IgE interact.
Mast cells have receptors for IgE and FcεRI (high affinity IgE receptor).
When do B cells produce the IgE needed for type 1 hypersensitivity?
B cells produce it when co-stimulated with IL-4 (secreted by TH2 cells)
IL-5: eosinophil maturation
Describe the genetics involved in allergy.
Filaggrin is expressed by keratinocytes and involved in maintaining epithelial barriers and moisturizing surfaces and controlling pH.
What are the clinical features of anaphylaxis?
- almost invariably symptoms begin. Within 60 minutes
- The later the onset the less severe the attack
- 20% have biphasic reaction 1-8hrs later therefore need steroids and hospital admission
What are the effects of adrenaline?
- reverses peripheral vasodilation
- Decreases angioedema
- Increases peripheral vascular resistance
- Causes bronchodilator
- Improves BP and coronary perfusion
- Decreases release of inflammatory mediators
What is the treatment of anaphylaxis?
- Begin ABCDE assessment and ask for senior help
- Secure airway and high flow oxygen
- IM adrenaline
- Secure IV access
- IV antihistamine, hydrocortisone, fluids
- Nebuliser salbutamol
What is the most common presentation to the allergy clinic in infancy?
Egg allergy
What constitutes a severe allergic reaction?
- Angioedmema of the airway
- Bronchospasm
- Hypotension
Describe the process of anaphylaxis
- Anaphylaxis is the most serious type of allergy
- Mast cells produce prostaglandins and leukotrienes through the cyclooxygenase and lipoxygenase pathways.
- The result is vasodilation and increased vascular permeability.
- Shift of fluids from the vascular to the extra-vascular space resulting in a fall in vascular tone.
- Severe drop in blood pressure.
- In the skin, mast cells release histamine further contributing to welling and fluid shift.
What are the effects of histamine?
Bronchial smooth muscle contraction
Vasodilation
Separation of endothelial cells (responsible for hives)
Pain and itching
