Immunology Flashcards
(42 cards)
What is allergy?
Hypersensitivity of immune system to allergens (proteins that immune system recognises as foreign & potentially harmful). Not all proteins/antigens will cause hypersensitivity reaction
The skin sensitisation theory is one of leading theories for allergy at present; describe the skin sensitisation theory
- Break in child’s skin that allows allergens to enter body and react with immune system
- Child does not have contact with the allergen in the GI tract/there is an absence of GI exposure to the allergen
- If, when weaned a baby regularly eats foods containing that allergen their GI tract is regularly exposed to the allergen and hence GI tract will recognise the allergen as food and not as a foreign or harmful protein
- Hence, theory is that regularly exposure to allergen through food and preventing exposure to allergen through skin can help prevent food allergies developing
Coombs & Gell classification has 4 types of hypersensitivity reactions; describe each
- Type 1: IgE antibodies to allergen trigger mast cells & basophils to release histamine & other cytokines. Immediate reaction. Allergy.
- Type 2: IgG and IgM react to allergen and activate complement system leading to direct damange to local cells (e.g. haemolytic disease newborn)
- Type 3: immune complexes accumulate & cause damage to cells (e.g. SLE, RA, HSP)
- Type 4: cell mediated; inappropriate activation of T cells resulting in inflammation & damage to local tissues (e.g. organ transplant rejection, contact dermatitis)
State some key aspects of potential allergy history
- Timing of reaction after exposure
- Previous & subsequent exposure to allergen
- Symptoms: rash, swelling, breathing difficulty, wheeze, cough
- Personal or FH of atopic conditions & alle
Allergies can be diagnosed on history alone; true or false?
True; is most important part; investigations can support diagnosis (and help determine exact allergies if uncertain)
State 3 investigations we can do for allergy
What is the gold standard and why?
- Skin prick testing (hypersensitivity)
- RAST testing (hypersensitivity
- Food challenge test
Food challenge test is the gold standard. Skin prick and RAST testing test for hypersensitivity; just because a child is sensitised it does not mean foods are unsafe to eat and child has allergy (i.e. a person can have IgE bound to mast cells but never experience allergy in their life). Food challenge test requires a lot of resources, time and is only available in certain places.
Explain how skin prick testing is done
- Draw grid on child’s forearm
- Put allergen solutions (that you want to test for) on squares alongside a histamine and water control
- Using fresh needle for each, make a break in skin at site of each allergen
- Assess after 15 minutes comparing size of wheals to the control#
- *NOTE: size of wheal does not indicate severity of allergy; it indicates sensitisation*
- **NOTE: must advise pts not to take antihistamine 72hrs before test*
Explain how RAST testing is done
- Take blood sample and measure total and allergen specific IgE
Explain how food challenges are done
- Done in specialist unit with close monitoring
- Gradually give child increasing quantities of allergen
- Monitor child after each exposure
Discuss the management of allergies (in general- not looking for anaphylaxis management)
- Establish/diagnose correct allergen
- Avoid the allergen
- E.g. avoiding certain foods
- E.g. regular hoovering, changing sheets & pillows if allergic house dust mites
- E.g. stay inside when pollen count high
- Prophylactic antihistamines if contact inevitable
- If at risk of anaphylaxis should be given adrenaline autoinjector
- May be offered immunotherapy (gradually expose to allergen over months)
Why should children be admitted after anaphylactic reaction?
Can have biphasic reaction therefore need admitting for period of observation
Discuss which children are given adrenaline autoinjectors
- All those with anaphylactic reactions
- Children with generalised allergic reactions with risk factors such as:
- Asthma requiring ICS
- Poor access to medical treatment (e.g. rural location)
- Adolescents (higher risk)
- Nut or insect sting allergies
- Significant co-morbidities
Different adrenaline autoinjectors exist and are to be used differently; summarise key points
- Remove safety cap
- Grip with fist with needle pointing down
- Inject into outer portion of mid thigh (can be done through clothing)
- Hold for up to 10 secs (3 secs in Epipen, 10 secs Jext)
- Remove injector
- Massage site for 10 seconds
- Phone ambulance
- Repeat in 5 mins if required
Remind yourself of treatment options for allergic rhinitis
- Avoid trigger (e.g. avoid outdoors in high pollen count, avoid pets, change pillows etc…)
- Oral antihistamines:
- Non-sedating: loratadine, cetirizine, fexofenadine
- Sedating: chlorphenamine (piriton), promethazine
- Nasal corticosteroids (e.g. fluticasone, mometasone)
- Nasal antihistamines
What age does cow’s milk protein allergy typically occur in?
Occurs in children <3yrs
Cow’s milk protein allergy can be IgE and non-IgE mediated; what is the difference between IgE and non-IgE mediated?
IgE mediated: rapid reaction (usually within 2hrs)
Non-IgE mediated: slower reaction (over several days)
See table for differences in symptoms
Describe presentation of cow’s milk allergy
Usually presents <1yr of age:
GI symptoms
- Bloating & wind
- Abdo pain
- Diarrhoea
- Vomiting
General allergic symptoms
- Urticarial rash
- Angio-oedema
- Cough
- Wheeze
- Sneezing
- Watery eyes
- Eczema
*in severe cases anaphylaxis may occur
Discuss the management of cow’s milk allergy
Management is centred around avoiding cow’s milk:
- Breastfeeding mum avoiding dairy
- Replacing formula with special hydrolysed formulas for cow’s milk allergy (still contain cow’s milk protein but proteins broken down so don’t trigger immune response)
- Replace with elemental (amino acid) formulas (if severe and cannot tolerate hydrolysed. Example is neocate)
Over time, about ~6 months try infant on first step of milk ladder then slowly progress up until develop symptoms; as time goes on should eventually be able to progress to normal diet containing milk. Most children grow out of milk allergy by age of 3-5yrs (IgE ~5yrs, non-IgE ~3yrs)
Explain the difference between cow’s milk intolerance & cow’s milk allergy
- Cow’s milk protein intolerance is not an allergic reaction.
- Cow’s milk protein intolerance will present with same GI symptoms as cow’s milk allergy but without allergic features (rash, angioedema etc..)
- Infants with cow’s milk intolerance will be able to tolerate cow’s milk & continue to grow & develop (but have GI symptoms when consume the milk) however those with allergy will not
Discuss the management of cow’s milk intolerance
- Avoid cow’s milk (e.g. breastfeed with mum avoiding dairy, hydrolysed formula, wean to foods not containing cow’s milk)
- After 1yr of age start on milk ladder
Which children with recurrent infections should be sent for further specialist assessment?
- Chronic diarrhoea since infancy
- Failure to thrive
- Appearing unusually well with quite severe infection (e.g. afebrile with large pneumonia)
- Significantly more infections than expected (particularly bacterial LRTIs)
- Unusual or persistent infections (e.g. CMV, PCP, candida)
What investigations would you consider in children who recurrent infections?
- Full blood count: low neutrophils suggest a phagocytic disorder and low lymphocytes suggest a T cell disorder
- Immunoglobulins: abnormalities suggest a B cell disorders
- Complement proteins: abnormalities suggest a complement disorder
- Antibody responses to vaccines, specifically pneumococcal and haemophilus vaccines
- HIV test if clinically relevant
- Chest xray for scarring from previous chest infections
- Sweat test for cystic fibrosis
- CT chest for bronchiectasis
What are primary immunodeficiency disorders?
State some examples
Rare, genetic disorders in which part of the body’s immune system is missing or functions improperly.
What is SCID?
Severe combined immunodeficiency (SCID) is the name given to a group of rare, inherited disorders that cause major abnormalities of the immune system. There are many different types of SCID, each with different genetic causes. Have almost no immunity. Have absent or dysfunctioning T and B cells
