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Year 2 Semester 4 Immune System > Session 2 > Flashcards

Session 2 Flashcards

1
Q

Epidemiology of allergy

A

Allergy is common:

  • Allergic rhinitis (AR) affects up to 30% of adults.
  • Asthma is diagnosed in >1 in 10 UK schoolchildren.
  • Food allergy is confirmed in about 6% of children.
  • Nearly half of UK adults suffer from at least one allergy.
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2
Q

Allergy and morbidity?

A
  • Allergy is associated with significant morbidity:
  • Persistent symptoms of AR impair sleep and reduce productivity.
  • Recurrent hospital admissions for asthma cause high absenteeism.
  • Restrictive diets in food allergy cause social exclusion and malnutrition.
  • Allergy can be fatal
  • Around 1200 people die from asthma in the UK each year.
  • Admissions for anaphylaxis increased >600% in the 20 years to 2012
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3
Q

Define allergen

A

Any substance stimulating the production of IgE or a cellular immune response. Usually a protein, but can be carbohydrates (much less common).

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4
Q

Define sensitivity (in the context of allergy)

A

Normal response to a stimulus.

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5
Q

Define hypersensitivity

A

Abnormally strong response to a stimulus.

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6
Q

Define sensitisation

A

Production of IgE antibodies (detected by serum IgE assay or SPT) after repeated exposure to an allergen.

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7
Q

Define allergy

A

Immunological hypersensitivity that can lead to a variety of different diseases via different pathomechanisms with different approaches in diagnosis, therapy and prevention”. This can be IgE mediated (e.g. peanut allergy) or non-IgE mediated (e.g. milk allergy).

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8
Q

Define atopy

A

A tendency to produce IgE antibodies in response to ordinary exposure to potential allergens. Strongly associated with asthma, rhinitis, eczema and food allergy.

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9
Q

Define anaphylaxis

A

A serious allergic reaction with bronchial, laryngeal and cardiovascular involvement that is rapid in onset and can cause death.

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10
Q

Define food

A

A substance, whether processed, semi-processed or raw, which is intended for human consumption (including drinks), and any substance used in the manufacture, preparation or treatment of food.

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11
Q

Define food allergy

A

An adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a food. Definition encompasses immune responses that are IgE- mediated or non-IgE mediated.

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12
Q

What are the 8 major allergic diseases

A

Allergic rhinitis (Hay fever) - Blocked/runny nose, itchy nose, sneezing. Triggered by pollen, pets or HDM.

Allergic Conjunctivitis - Red, swollen, itchy, watery eyes. Can occur with allergic rhinitis.

Asthma - Chest symptoms of wheeze, cough, shortness of breath and tight chest. Not always allergic.

Atopic dermatitis eczema - Commonest chronic inflammatory skin disease with itch and excoriation

Urticaria (Hives) - Acute/chronic (±6w) maculo-papular pruritic rash without or with angioedema

Insect allergy - Mainly to bee or wasp stings. Mild (local), Moderate (urticaria) Severe (anaphylaxis)

Drug allergy - Especially to antibiotics, but only a minority who are labeled drug allergic are truly allergic.

Food allergy - Clinically broad symptom spectrum varying in timing of presentation and in severity.

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13
Q

How does allergy and sensitisation change with age?

A

Eczema and food allergy tends to improve with age. Asthma worse during teenage years but then improves. Rhino conjunctivitis tends to worsen with age.

Sensitisation follows same trend.

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14
Q

What is a milk allergy?

A

Immunologically mediated hypersensitivity reaction to milk.

  • Commonest food allergy in infants – affects 2-3%.
  • Always presents by 12 months of age.
  • Symptoms can present many weeks after first ingested.
  • Two types of presentation:
  • Immediate-onset IgE mediated (40%)
  • Typical allergy symptoms affecting skin, respiratory and GI tracts.
  • Symptoms of urticaria, cough, wheeze, vomiting and diarrhoea.
  • Can cause anaphylaxis and even be fatal.
  • Delayed-onset non-IgE mediated (60%)
  • Predominantly multiple GI symptoms.
  • Difficult to diagnose: younger presentation similar to colic, reflux.
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15
Q

What are the 14 major food allergies that cause anaphylaxis?

A

Celery

Cereals containing gluten

Crustaceans

Eggs

Fish

Lupin

Milk

Molluscs

Mustard

Nuts

Peanuts

Sesame seeds

Soya

Sulphur dioxide (sometimes known as sulphites)

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16
Q

Define food intolerance

A

Numerous (frequently reported) adverse responses to foods that do not involve an immune response.

17
Q

What is the prevalence of food allergy?

A

Although more than 170 foods have been reported to cause IgE-mediated reactions, prevalence studies have focused on most common foods – milk, eggs and peanuts. Prevalence of self-reported food allergy can be 6x higher than proven allergy; nevertheless more prevalent in children – 6% vs 1-2% in adults.

18
Q

Summarise the differences between immune mediated and non-immune mediated adverse food reactions

A
19
Q

How does food allergy presentation differ between IgE mediated and non IgE mediated?

A

FPIES - Food protein induced enterocolitis syndrome

20
Q

What are the different presentations of immediate-onset food allergy

A
21
Q

What are the different presentations of delayed-onset food allergy?

A
22
Q

What is the food allergy march?

A

‘Food allergy march’ – change in food allergies with increasing age

23
Q

What is the effect of temperature and food matrix on common food allergens?

A
24
Q

How does food processing/cooking affect allergy presentation in food?

A

Food processing destroys conformational (folded) epitopes making them less allegenergic.

25
Q

Implications of cross-reactive food allergens

A
26
Q

Summarise food allergy presentation

A
  • A third of people report adverse reactions to foods.
  • Most common reactions are not immune mediated.
  • True food allergy has two major phenotypes:
  • IgE mediated or immediate-onset
  • Non-IgE mediated or Delayed-onset
  • Different presentations in each phenotype.
  • ‘Food allergy march’ describes different food allergy timing.
  • Processing affects allergenicity by altering proteins.
  • Varying degrees of cross-reactivity amongst ‘related’ foods.
27
Q

How do you make a food allergy diagnosis?

A
28
Q

What are the essential elements of a medical history in suspected food allergy?

A

Context

Thorough description of reaction:

  • Age of onset.
  • Complete list of all foods suspected of causing symptoms.
  • Route of exposure (ingestion, skin contact, inhalation).
  • Activity at time of exposure (exercise or alcohol can potentiate reaction).
  • Any intercurrent illness at time of reaction (can mimic allergic reaction).
  • List of foods previously ingested without symptoms.

Symptoms

  • All observed symptoms and each one’s severity.
  • Timing of symptom onset in relationship to food exposure.
  • Duration of symptoms, treatment provided and response to treatment.

Food

  • Manner in which food was prepared (cooked, raw, added ingredients).
  • Minimal quantity of food exposure required to cause symptoms
29
Q

How can skin prick tests be used to diagnose food allergies?

A

Placing allergen on skin and pricking the skin with a prick lancet, being careful not to break the skin and if allergic, a reaction will show.

30
Q

How can immunoassays be used to detect allergen-specific IgE?

A

Typical immunoassay for detection of specific IgE in 3 steps

  1. Allergen is adsorbed and immobilised to a solid phase.
  2. Patient’s serum is added followed by incubation for 30-60 minutes followed by several washing steps.
  3. Allergen-bound IgE is detected by an enzymatically labeled anti-human IgE monoclonal antibody.

Most commonly used techniques

  • ELISA-Plates, Western blots
  • Strips, ImmunoCAP, Microarrays
31
Q

How can using sIgE screening tests in immediate onset symptoms help diagnose food allergy?

A
  • Detect IgE:
  • Serum specific IgE – IgE circulating in blood
  • Skin prick tests – Response of skin mast cells to allergens
  • Determine presence of sensitivity not allergy
  • Level of sIgE / size of SPT correlates with likelihood of allergy
  • Positive predictive thresholds developed for common allergens
  • Do not correlate with or predict severity of allergic reaction
  • Test selection determined by: Clinical history, Possible cross-reactivity, Targeting likely allergens
32
Q

What are the treatment options for management of a food allergy?

A
  • Appropriate assessment first
  • Allergy focused history and examination.
  • Appropriately selected allergy investigations.
  • Identify food causing symptoms.
  • Dietary advice
  • Exclusions – which food/food groups/food formats to avoid.
  • Inclusion – which food/groups/formats not to avoid.
  • Label reading: Ingredient labeling. Patient Advisory Labels.
  • Food reintroductions.
  • Medical advice
  • Emergency management of allergic/anaphylactic reaction.
33
Q

Management of a milk allergy?

A

Adult - just avoid milk containing products.

Babies - Use formula milk instead. Soya milk optional. Extensive hydrolysed formula - amino acid chains are broken down to reduce allergenicity. Small amount of protein left over though so those babies who are more sensitive will use amino-acid formula and do not contain any milk proteins, instead using plant based proteins. Not used initially as expensive.

Dairy-free weaning advice followed by milk introduction after 12 months.

34
Q

What is Lactose intolerance?

A

Deficiency in the enzyme, lactase.

Lactase evolution and action

  • Detection from 8 weeks gestation; rise from 32 weeks to peak at birth.
  • Activity decreases within months.
  • Present on jejunal brush border apex.
  • Hydrolysis of lactose into monosaccharides galactose and glucose

Lactose intolerance (Lactase non-persistence)

  • Occurs in most humans; variable.
  • Typical symptoms: bloating, flatulence, explosive diarrhoea.
  • Onset subtle; progressive over years.
  • Most diagnosed as adolescent or adult.
  • Not always symptomatic with milk
35
Q

What is the milk ladder?

A

Milk reintroduction using the ‘Milk Ladder’ as part of management for patient with milk allergy.

36
Q

Management of food induced anaphylaxis

A

Dietary advice

  • Dietary exclusions and inclusions.
  • Reading labels. - Look for 14 ‘major’ allergens. - Appear in bold.
  • Managing risk: Eating out and Take-aways. - ‘May contain traces’

Medical advice - how to use epipen

37
Q

Can food allergy cause eczema?

A

No

Year 2 Semester 4 Immune System (4 decks)

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