Immuno: Case Studies in Immunology Pt.1 Flashcards
Define anaphylaxis.
A systemic hypersensitivity reaction in which the response is so overwhelming that it can be life-threatening
Describe the mechanism of type I hypersensitivity reactions.
- Cross-linking of IgE on mast cells by an antigen causes degranulation
- The release of various mediators including histamines and leukotrienes results in increased vascular permeability, smooth muscle contraction, inflammation and increased mucus production
List some clinical features of anaphylaxis.
- Conjunctival injection
- Rhinorrhoea
- Angioedema
- Urticaria
- Wheeze/bronchoconstriction
- Laryngeal obstruction/stridor
- Hypotension
- Cardiac arrhythmias
- Vomiting, diarrhoea, abdominal pain
What is the most common clinical feature of anaphylaxis?
Urticaria
Outline the management of anaphylaxis.
- ABCDE approach
- Respiratory support if necessary
- Oxygen by mask
- IM adrenaline (0.5 mg)
- IV antihistamine (10 mg chlorpheniramine)
- IV corticosteroid (200 mg hydrocortisone)
- IV fluids
- Nebulised bronchodiliators
NOTE: steroids take about 30 mins to start working but they are important in preventing rebound anaphylaxis
Describe the mechanism of action of adrenaline in anaphylaxis.
- It stimulates beta-2 receptors causing constriction of arterial smooth muscle
- This leads to increased blood pressure, limits vascular leakage and has a bronchodilator effect
Define positive trypase test
> 1.2 x baseline +2
List some common causes of anaphylaxis.
- Foods: peanuts, fish, shellfish, milk, eggs, soy
- Insect stings: bee venom, wasp venom
- Chemicals, drugs and other foreign proteins: penicillin, IV anaesthetic, latex
What is latex?
Milky fluid produced by rubber trees (Hevea brasiliensis)
What are the two types of latex allergy and how do they typically present?
Type I Hypersensitivity
- Acute onset of classical allergic symptoms soon after exposure (e.g. wheeze, urticaria, angioedema)
- Spectrum of severity
- Occupational exposure can lead to symptoms similar to asthma (e.g. lab workers)
Type IV Hypersensitivity
- Causes contact dermatitis (very itchy, well demarcated rash)
- Usually affecting the hands and feet (due to gloves and footwear)
- Symptoms begin 24-48 hours after exposure
- Not responsive to antihistamines
Which patient groups are particularly susceptible to type I hypersensitivity reactions to latex?
- Patients undergoing multiple urological procedures
- Preterm infants
- Patients with indwlling latex devices (e.g. ventriculoperitoneal shunt)
What can a type I hypersensitivity reaction to latex cross-react with?
- Avocado
- Apricot
- Banana
- Passion fruit
- Papaya
NOTE: basically quite a lot of fruit
Name and describe three types of test for hypersensitivity.
- Specific IgE - this is a blood test that is preferentially used in patients with a history of anaphylaxis
- Skin prick testing
- Patch testing - patch is pasted onto the skin for 24-48 hours and eczema will be seen if there is a reaction
Describe the appearance of biopsy of urticarial tissue in anaphylaxis.
- Infiltrating T cells
- Granulomas
Which subset of patients should be referred to an allergist/immunologist?
All patients after anaphylaxis
Investigations in SLE
Screen all lupus patient for APS antibodies
Describe the mechanism of action of serum sickness.
- Penicillin binds to cell surface proteins
- This acts as a neo-antigen, which stimulates a very strong IgG response
- This means that the individual is sensitised to penicillin
- Subsequent exposure leads to the formation of immune complexes with the penicillin and the production of more IgG antibodies
- Immune complexes deposit in joints, kidneys and skin causing arthralgia, glomeruloephritis and a vasculitic rash
