Allergies

Question 1

What is an allergy?

Answer 1

• Exaggerated immune response to a non-microbial/ environmental antigen.
• Over production of immunoglobulin E (IgE).
• Involve cytokines IL-4,5 & 13 produced by Th2 cells, IgE, mast cells and eosinophils.

Question 2

What is atopy?

Answer 2

Genetically determined, exaggerated IgE-mediated immune response
- Type 1 hypersensitivity disorders e.g. hay-fever, asthma

Question 3

What are the types of allergic disease?

Answer 3

Asthma, rhinitis, urticaria & angioedema and eczema

Question 4

What is asthma?

Answer 4

Chronic disorder of airways with variable airflow limitation.
- Recurrent episodes of wheezing, breathless, tight chest, cough.
- Inhaled allergen - most common

Question 5

What is rhinitis?

Answer 5

Respiratory disease linked with asthma
- Nasal congestion ,itching and sneezing

Question 6

What is urticaria and angioedema?

Answer 6

Raised, itchy nettle rash - like hives
- Triggers; food and drug allergens e.g. NSAIDs, ACEIs

Question 7

What is eczema?

Answer 7

Local inflammation of the skin
- appears in early childhood induced by food e.g. eggs, milk

Question 8

Describe anaphylaxis.

Answer 8

Severe allergic reaction - life threatening/ death
Systems involved; respiratory, blood, cardio and gastro
Allergen triggers; food, drugs - antibiotics, venoms latex

Question 9

Describe genetic predisposition.

Answer 9

• Influenced by inheritance of several genes/chromosomes.
• Identification of susceptibility locus for atopy on chromosomes 5q, near site of gene cluster encoding cytokines IL-4,5,9 &13

Question 10

What is the hygiene hypothesis?

Answer 10

Cleaner environment = less microbes

Question 11

Describe the skin prick test.

Answer 11

1. Gold standard method - drop of allergen on skin, small skin prick, skin reaction - local tissue swelling and degranulation.
2. Test selection of allergens according to clinical history.
3. Pt must not be taking antihistamines as it will diminish sensitivity of test - false negative.
4. Controls; histamines (+ve), saline (-ve).

Question 12

Describe allergen sensitisation.

Answer 12

Exposure to an allergen leads to IgE production which results in 2 events.
- Differentiation of Tcells to Th2
- Stimulate B cells to switch to IgE production - Th2 cells produce cytokines and provide CD40 ligand to lead antibody class switching.

Question 13

What are the roles of mast cells and basophils?

Answer 13

Initiate acute inflammatory response
Basophils - reside in circulation
Mast cells - function as immune sentinel cells and produce cytokines.

Question 14

Where are mast cells found?

Answer 14

In connective tissue surrounding blood vessels and mucosal surfaces.

Question 15

What is the granule contents of mast cells?

Answer 15

Histamine
Leukotrienes
Inflammatory cytokines
Neutrophil and eosinophil attracting cytokines

Question 16

What is the granule contents of eosinophils?

Answer 16

• T and B cell attracting chemokines
• Fibrotic cytokines
• Matrix metalloproteinases and collagenases

Question 17

What is the early phase of allergic response?

Answer 17

• Physiological mechanisms
• Loss of organ function due to; mucus production, vasodilation and swelling, bronchoconstriction.

Question 18

What is the late phase response of allergic response?

Answer 18

• Immunological mechanisms
• Smooth muscle scarring
• Recruitment of immune cells into peripheral tissues

Question 19

What is the immediate phase response of allergy?

Answer 19

• Mast cell degranulation
• Histamine release

Question 20

What is the late phase allergy response?

Answer 20

• Immune response
• Eosinophil migration