Immunology Flashcards
What is an allergy?
An inappropriate hypersensitivity response to a normally harmless allergen. Can be IgE mediated, or non-IgE mediated.
What is sensitisation?
Production of IgE antibodies after repeated exposure to an stimulus.
What is atopy?
A tendency to produce IgE antibodies in response to ordinary exposure to potential allergens.
What are some conditions you might have if you are “a bit atopic”?
Eczema
Asthma
Rhinitis
Food allergy
What is a food allergy?
An immunologically mediated adverse reaction to food.
How does allergic rhinitis present?
What is it also known as?
Blocked runny nose
Itchy nose
Sneezing
Hay fever
What can trigger allergic rhinitis?
Pollen
Pets
House dust mites
A child is brought to you because of chronic itchy red swollen and watery eyes. What immunological differential might you consider?
Allergic conjunctivitis
What is urticaria?
Hives - acute or chronic maculo-papular pruritic rash.
May or may not have angioedema.
When might a child have urticaria?
After a bee/wasp sting with a moderate reaction.
Other than food, what can children be allergic to?
Insects Latex Drugs House dust mites Animals Moulds Pollen
How does allergy presentation change with age?
Food allergy and eczema present earliest, with a peak in asthma presentation slightly later again, then allergic rhinitis incidence increases with age.
What is the hygiene hypothesis?
Lack of childhood/early exposure to allergens increases susceptibility to allergic disease due to suppression of natural immune system development.
What is the dual-allergen exposure hypothesis?
Early oral exposure to food allergens induce tolerance, but early cutaneous exposure to food proteins leads to sensitisation.
What are the 5 Ds of food allergy prevention?
Dry skin (prevent, manage eczema)
Vitamin D
Diet (early weaning, varied diet)
Dogs and Dribble (sharing microbes is good/hygiene hypothesis)
A 12 week old girl presents with vomiting after feeds, hungry but difficult to feed, irritable, and in pain. She has been formula fed since birth.
What are your differentials?
Milk allergy
GORD
Intestinal obstruction
How do non-IgE mediated allergies to food tend to present?
With GI symptoms and failure to thrive, as well as skin symptoms such as pruritis/eczema.
Presentation tends to be delayed compared to exposure.
What are the most common foods that children can be allergic to?
Milk
Eggs
Peanuts
How is lactose intolerance different to a food allergy?
It is metabolic and non-immune mediated, where as true food allergies are immune mediated.
It is still an adverse food reaction.
Other than lactose intolerance, what other non-immune mediated adverse food reactions can people have?
Pharmacological e.g. to caffeine
Toxic e.g. Scromboid fish poisoning
Psychological (food aversion)
Tell me about scromboid food poisoning.
Foodborne illness from spoiled fish.
Bacteria convert histidine to histamine which is unaffected by cooking.
How does scromboid food poisoning present?
10-30 minutes after ingestion -> facial flushing, sweating, headache, dizziness, nausea.
Later -> facial rash (itchy), urticaria, abdominal cramps, diarrhoea, bronchospasm.
What is the pathophysiology of lactose intolerance?
Lactase enzyme activity decreased so lactose ferments in the gut -> diarrhoea, flatulance, and bloating.
A child presents with suspected food allergy.
How would knowing the onset timing help with diagnosis of type of allergy?
IgE mediated onset is immediate to within half an hour.
Non-IgE mediated is delayed (hours to days)
Which foods are more likely to have a non-IgE mediated allergic reaction?
Milk and soya
Wheat
Oats
Rice
Which foods are more likely to have an IgE mediated allergic reaction?
Milk Eggs Peanuts Tree nuts Fish and shellfish Fruits and vegetables
Define anaphylaxis.
Rapidly progressive, potentially fatal, multiple organ system reaction with respiratory symptoms to an allergen.
What can we do to some foods to make them less allergenic?
How can we use this?
Cook it! Denatures proteins, or binds it to other foods for reduced effect.
Use to gradually expose children to foods they are allergic to, in order to desensitise them.
A 2 year old present with blood in their stool, which is also mucousy. They are otherwise well and has no other symptoms.
What food allergy presentation might you consider here?
Proctocolitis
What is pollen food syndrome?
Food allergy to fresh fruit and vegetables which usually presents in adolescence.
What makes it possible for a milk-allergic person to tolerate baked milk?
Casein is more heat resistant than whey, so high temperatures denature some of the proteins.
Bonds are formed with wheat when baking to reduce availability and allergenicity.
Is a well cooked whole egg more or less allergenic than raw egg?
Much less allergenic when cooked - 70% of egg-allergic can tolerate baked egg.
What forms of fish are less allergenic?
Canned tuna and salmon.
Cooking fish does not reduce allergenicity as fish protein is very stable.
What can patients with pollen food syndrome tolerate?
Processed or cooked apple as apple proteins are very heat sensitive.
A child presents with some food allergies. Mum is worried about what else he might be allergic to.
What associations might we look at to investigate further?
Cows milk allergy can be associated with goats milk allergy.
One tree nut allergy assoc. with other tree nut allergy, as with one fish and other fish, and one shellfish and other shellfish.
Makes sense really.
You do a skin prick test on a young boy who is quite atopic. He has eczema, and a few known allergies, but mum wants to know specifically about shellfish.
What phenomenon means that you may not be able to tell her if he is allergic to shell-fish or not?
Cross-reactivity.
Eczema is partly allergy to house dust mites, and there is cross-reactivity between shellfish and HDM. If the skin prick test is definitely negative, then he is not allergic to shellfish, but if it is positive that may be a false positive from HDM allergy.
How is skin prick testing done?
A drop of liquid containing the allergen is put onto the forearm. The skin under the arm is gently pricked.
The patient waits 15 minutes.
If they are allergic to the substance, a wheel will appear. To be positive, the wheal must be more than 2mm wider than the negative saline control.
What do you need to tell parents about skin prick testing?
Don’t give the child antihistamine before the skin prick test as it will interfere with results.
Very safe test.
May be a little uncomfortable for the child, but not painful.
What do IgE assay tests show when thinking about allergy?
They show sensitisation, not clinical allergy.
How can we manage food allergies?
Don’t cut out food groups!!
Dietician-led follow-up with gradual exposure to food groups known to be allergenic.
Symptoms management e.g. anti-reflux medication
Anticipatory allergy testing
Emergency medication prescription where necessary.
When are the first UK immunisations scheduled?
At 2 months of age
Which immunisations are given at 2 months?
6 in 1
PCV
Rotavirus
Meningitis B
Which immunisations are given at 3 months?
6 in 1
Rotavirus
Which immunisations are given at 4 months?
6 in 1
PCV
Meningitis B
Which immunisations are given at 12-13 months?
Hib/MenC combined
MMR
PCV
Meningitis B
What is in the 6 in 1 vaccination?
Diptheria Tetanus Pertussis Polio Haemophilus influenzae type B Hepatitis B
Which immunisations are given at 3 years?
Preschool 4 in 1 booster
MMR (dose 2)
What is in the preschool 4 in 1 booster?
Diptheria
Tetanus
Pertussis
Polio
Which immunisations are given at 12-13 years?
HPV for girls (currently) with a second injection 6-12 months after first injection.
Which immunisations are given at 14 years?
3 in 1 injection
Men ACWY
What is in the 3 in 1 injection?
Diptheria
Tetanus
Polio
When are vaccines contra-indicated?
If the pt has had a confirmed anaphylactic rxn to previous dose containing the same antigens or another component contained in the relevant vaccine.
Which are the live vaccines that we give to children routinely?
MMR
Rotavirus
Nasal flu vaccine (offered to preschool age)
What are the contraindications for giving live vaccines?
- Immunosuppressed pts
- Pregnancy (but that’s not relevant in this block)
How are immunodeficiencies classified?
As primary or secondary
What are primary immunodeficiencies due to?
Single-gene inerited disorders
What are the 4 main types of primary immunodeficiency by pathophysiology? How common are they?
B-cell defects (50%) T-cell defects (30%) Phagocytic deficiency (18%) Complement deficiency (2%)
What can cause secondary immunodeficiency?
- Lymphoreticular malignancy
- Drugs (esp. cytotoxic/immunosupps)
- Viruses (HIV)
- Malnutrition
- Metabolic disorders
- Trauma/major surgery
- Protein loss
What is the most common presentation of immunodeficiency?
Frequent infections
What specifically about recurrent infections is a good indicator for immunodeficiency?
Severe, persistent, recurrent, and bacterial infection.
Also infections by unusal organisms or opportunistic infections such as Pneumocystis jirovecci, CMV, or Candida.
What from a Hx would point to immunodeficiency?
FHx - early death, similar symptoms, autoimmunity, allergy, early malignancy, intermarriage.
RFs - diabetes, meds, iliicit drugs, sexual hx if older child.
Frequency of prev. abx prescription.
Radiotherapy esp. to thymus/nasopharynx
How do immune deficient children look O/E?
They look ill - pale, malaised, cachexic, distended abdo etc.
Signs of severe, multiple and/or specific infections present.
What Ix should be done in suspected immunodeficiency?
FBC - confirm presence of infection IgG IgM IgA ESR/CRP
Swabs (look for unusual organisms)
What lifestyle advice is given for immune deficient pts?
Healthy lifestyle Avoid infection Regular dental check-ups Regular accommodation checks Killed vaccine regime if any antibody response Education in recognising infection early
What medical management can we use for immune deficiency?
- Early recognition of infection
- Antivirals asap
- Immunoglobulin replacement as appropriate
- Bone marrow transplant for T cell deficiency
Define eczema.
A chronic relapsing inflammatory skin condition characterised by an itchy red rash that favours the skin creases (e.g. folds of elbows and behind knees)
What proportion of eczema cases present before age 5?
80%
What are the environmental trigger factors for eczema?
- Irritants (soap/detergents)
- Skin infections
- Contact allergens
- Extremes of temperature and humidity
- Abrasive fabrics
- Dietary factors in about half of children
- Inhaled allergens
What endogenous factors can tirgger eczema?
Stress and hormonal changes (esp. in girls/women)
How is eczema diagnosed?
Clinically, based on an ithcy skin condition + 3 or more of the following:
- Hx of itchiness on skin creases
- Hx of asthma or hay fever
- General dry skin in preceeding year
- Visible flexural eczema
- Onset in first 2 years of life
What does an acute flare up of eczema look like?
Varied - vesicles to poorly demarcated redness.
How is eczema different in infancy in terms of distribution?
Tends to affect face, scalp, and extensor surfaces in infants.
What conditions is atopic dermatitis associated with?
Asthma
Hay fever
Allergic rhinitis
Broadly, how should eczema be managed?
- Information and education
- Psychological support
- Avoid tirggers
- Hydrate skin
- Step-wise approach to medical management
What should form the basis of eczema treatment?
Emollients, used even when the atopic eczema is clear.
Tell me about the application of emollients.
Best when skin is moist. Apply liberally and frequently (every 3-4 hours a day), even when eczema is clear.
Prescribed in large quantities to facilitate this.
What kind of steroids are used on facial and flexural eczema?
Mild corticosteroids
What kind of steroids are used on discoid, scalp, limb, trunk, or lichenified eczema?
Potent corticosteroids
How frequently should topical steroids be applied for eczema?
Once or twice a day
How should bacterial infection of eczema be managed?
Topical emollient with antimicrobials can help prevent infection.
Oral abx usually necessary (14 day course, usually oral flucloxacillin)
When does lichenification of eczema occur?
After repeated scratching
How should lichenification of eczema be managed?
Initially with potent corticosteroid, then use bandages with paste to reduce itching, as well as coal tar and ichthammol in chronic eczema.
What can we escalate to if atopic dermatitis is not managed by maximal topical corticosteroid treatment?
Tacrolimus or pimecrolimus topical preparations
What is the prognosis associated with childhood eczema?
Gradual improvement into adult life.
60-70% of children will be clear by early teens.
If asthmatic or early onset, worse prognosis/longer duration.
