Immuno 1: Hypersensitivity and allergy: part 4 Flashcards
What are the three things in asthma that cause airway narrowing
Airway wall oedema (due to vascular leakage) mucus secretion and airway smooth muscle contraction (NOTE: these are all due to the mediators released from the mast cell activation and degranulation)
What happens upon exposure to asthama causing antigen to peak flow
PEF starts at less than 100% (as asthmatic so reduced anyway) EARLY RESPONSE: Initially, there is a rapid and significant reduction in PEF in response to antigen exposure. This is due to the immediate hypersensitiviy (IgE mediated, mast cell activation, acute airway narrowing due to the oedema, mucus and contraction) This recovers quickly (within an hour) However, over 2-8hrs there is then another reduction in PEF , the LATE RESPONSE: There is cell-mediated delayed type hypersensitivity in which lymphocyte and eosinophil mediated infmallation occurs (Th2 cells activate eosinohils, leading to IL4 and IL5 release) Important to remember that asthma is a mixture of type I and type IV. This graph is on somebody who has already been sensitised to antigen and had subsequent exposures already. So what happens when you give them allergen You get type I reaction straight away (due to IgE cross-linking) Then later you get cell mediated type IV reaction which is when Th2 activates eosinophils. This is not accounted for by type I, which only involves mast cell/basophil degranulation
Outline the chronic airway inflammation in asthma
So we had early and late response which are referring to acute onset inflammation Not there is also CHRONIC INFLAMMATIONlON 1. Cellular infiltrates (Th2 lymphocytes and eosinophils, from delayed type hypersensitivity) 2. Smooth muscle hypertrophy 3. Mucus plugging 4. Epithelial shedding 5. Sub-epithelial fibrosis
What are the important clinical features of asthma
REVERSIBLE generalised airway obstruction (–> chronic episodic wheeze) Bronchial hyperresponsiveness (–>bronchial irritability) Cough Mucus Breathlessness Chest tightness Responds to treatment (COPD doesn’t) Spontaneous variation Reduced and variable PEF
What are the important clinical features of allergic rhinitis
Note the mechanism is very similar to asthma in terms of type 1 and then type 4 Seasonal (hay fever, grass, tree pollens) Perennial (house dust mites or pets) Symptoms: sneezing, rhinorrhoea, itchy nose and eyes, nasal blockage, sinusitis, loss of smell/taste
Outline the clinical features of allergic eczema
I think this is the same as contact dermatits so it is type 5 Chronic itchy skin rash Flexures of arms and legs HDM sensitisation and dry cracked skin Complicated by bacterial and (rarely) viral infections (early childhood, herpes simplex) 50% clears by 7 years 90% by adulthood
Outline the important clinical features of food allergy
Mild: itchy lips, mouth, angioedema, urticaria Severe: nausea, abdominal pain, diarrhoea, collapse, wheeze, ANAPHYLAXIS
What are the most common food allergens in infants and adults
Infancy-3yrs egg, cows milk Children/adults peanut, nuts, shell fish, fruits, cereals, soya
What is anaphylaxis
severe generalised allergic reaction Generalised degranulation of IgE sensitised mast cells
Symptoms of anaphylaxis
itchiness around mouth, pharynx, lips swelling of the lips, throat and other parts of the body wheeze, chest tightness, dyspnoea faintness, collapse diarrhoea & vomiting death if severe & untreated
Which systems are involved in anaphylaxis
Systems: Cardiovascular - vasodilatation, cardiovascular collapse Respiratory - bronchospasm, laryngeal oedema Skin - vasodilatation, erythema, urticaria, angioedema GI - vomiting, diarrhoea
How can food allergens be tested
Careful history essential Skin prick testing RAST (blood specific IgE): Total IgE Lung function (asthma)
What is the emergency treatment of anaphylaxis
EpiPen & Anaphylaxis kit –>antihistamine, steroid, adrenaline –> Seek immediate medical aid
How is anaphylaxis prevented
Avoidance of known allergen Always carry a kit & EpiPen Inform immediate family & caregivers Wear a MedicAlert® bracelet
How is allergic rhinitis treated
anti-histamines (sneezing, itching, rhinorrhoea) nasal steroid spray (nasal blockage), if the inflammation is cell mediated (anti-histamine only helps if it’s just due to type 1) cromoglycate (children, eyes)
