Lecture 22 - Food Allergy Flashcards
Characterise the prevalence of immune disorders
Since 1950: • Exponential increase in immune disorders - MS - Type I diabetes - Asthma - Crohn's disease - Food allergy & anaphylaxis
The increase is seen across all age groups, but children 0-4 in particular
What is anaphylaxis?
Most severe form of allergic reaction
Rapid onset
May cause death
What are the determinants of allergic disease?
- Genes
- Early life environment:
• Microbial exposure (most important)
• Vit D
• UV light
• Diet
Describe the effect of genetics and environment leading to disease
- Genes & environment
- Epigenetic modification
- Gene expression
- Altered immune tolerance
- Disease
Describe the observations from studies of mice in germ free conditions
“Fail to develop oral tolerance”:
• Underdeveloped Peyer’s patches lacking GCs
• Few IgA plasma cells and CD4+ T cells in LP
• Reduced n° of IELs
• Fail to develop oral tolerance
• Persistent Th2 responses
Window of opportunity:
• These abnormalities can be reversed, but only in the neonatal period
Compare intestinal microbiota in allergic and non-allergic children
Allergic:
In general:
• Decreased levels of probiotic bacteria
• Increased levels of pathogenic bacteria
- ‘Good’ Bifidobacterium levels reduced and less adherent to intestinal mucous
- Microbiota induce less IL-10 production
Which bacteria are probiotic?
Which bacteria are pathogenic?
Probiotic:
• Lactobacillus
• Bifidobacteria
Pathogenic:
• C. difficile
• S. aureus
When is abnormal microbiota seen in children?
Preceding the development of allergic disease
Describe the changes to microbiota over the first 12 months of life in children who will develop allergic disease
1 month:
• decreased bifidobacteria
• decreased colonisation of Enterococci
• increased Clostridia
6 months:
• increased Staphylococcus
12 months:
• decreased Bacteroides
Why is microflora important for disease?
Intestinal microflora plays a vital role in:
• Immune system maturation
• Development of tolerance
Which are required to avert allergic responses
What is the prevalence of food allergy?
2% - 5% of population
Which group of people most common experience food allergy?
Children: 6-10%
Compared to
Adults: 2%
Food allergies resolve with age
What are the major food groups that cause allergy?
In order of increasing prevalence: • Peanuts • Tree nuts & seeds • Fish • Crustaceans • Eggs • Milk products • Fruit & veg • Food additives • Wheat
8 major food groups cause > 90% of food allergy
What are the common food allergies in children?
Compare this with adults
Children:
• Egg, milk, peanut
• Soy, wheat, fish
Adults:
• Peanut, tree nuts, fish, shellfish
What are the various clinical symptoms caused by the IgE mediated allergic reaction?
- Urticaria
* Angioedema
What is urticaria?
Hives:
• IgE mediated allergic reaction
• Red bumps on skin
• Similar to angioedema, but only occurs in the upper dermis
What is angioedema?
Rapid swelling of dermis, subcutaneous tissue, mucosa & submucosa
Around eye
What are the symptoms in the following regions due to the IgE mediated allergic reaction?
• Airway
• Cardiovascular system
1. Airway • Hoarse voice • Difficultly swallowing & breathing • Feeling of tightness in throat • Coughing • Wheeze
- Cardiovascular
• Drowsy
• Collapse
• Pale and floppy
How is food allergy managed?
• Allergen avoidance
• Education:
- management of allergic reactions - preparation for anaphylaxis
• Adrenaline auto-injector
Is allergen avoidance successful?
No, it’s difficult
- 50% of children have accidental ingestion within 1 yr
- In fatal cases most were aware of the allergy but failed to avoid the food
- 40-100% of fatal reactions were from food prepared outside the home
Is the EpiPen widely used?
- 75% carried it
- 10% were expired
- 32% could use it correctly
Requires regular training
- Even when used, person can die:
- In 12-14% of fatal cases there were early, repeated doses of adrenaline
Describe the mechanism for loss of tolerance to food
- Increased Th2, decreased Th1
- Reduced Treg numbers & activity
- Allergen in gut
- Allergen taken up by DCs
- Allergen presentation to Th2
- Stimulation of B-cells to produce IgE
→ Food allergy
What was observed in the immune response in resolution of food allergy?
- Shift to Th1 responses
* Increased allergen specific Tregs
Compare Desensitisation & tolerance
How are they measured?
Desensitisation: the ability to tolerate a food while ingesting regular doses of the food
• Rapidly reversible
• Mediated by changes in effector cells (mast cells, basophils)
Tolerance: Ability to tolerate a food after a period of time has elapsed since ingesting the food
Expected to last for months-years after stopping therapy
Measured by:
Desensitisation: oral food challenge whilst still on treatment
Tolerance: oral food challenge after stopping therapy
