Allergy

Question 1

What are the common names for hypersensitivity I, II, III, IV

Answer 1

I= Anaphylactic
II= Cytotoxic
III= Immune complex
IV= Delayed type

Question 2

Describe type-II hypersensitivity

Answer 2

• Antibody = IgG, IgM against combined self/foreign antigen
• Antigen= cell surface
• Response time= minutes/hours
• Appearance= lysis & necrosis
• Innocuous antigen= penicillin
• Histology= Antibody & complement
• Associated diseases= Erythroblastosis fettles, Goodpasture’s nephritis

Question 3

Describe type-III hypersensitivity

Answer 3

• Antibody= IgG, IgM
• Antigen= Soluble
• Response time= 3-8hours
• Appearance= Erythema, oedema, necrosis, vasculitis
• Innocuous antigen= mouldy hay-farmer’s lung
• Histology= Complement & neutrophils
• Associated diseases=SLE

Question 4

Describe type-I hypersensitivity

Answer 4

• Antibody= IgE
• Antigen= Exogenous
• Response time= 15-30mins
• Appearance= Weal & flare
• Histology= Basophils & eosinophils
• Innocuous antigen= pollen-hay fever

Question 5

Describe type-IV hypersensitivity

Answer 5

• Antibody= None
• Antigen= Tissue & organ specific T-cell mediated cytotoxicity
• Response time= 48-72 hours
• Appearance= erythema induration
• Histology= monocytes & lymphocytes
• Innocuous antigen= Poison ivy, tuberculin test, metals-nickel
• Associated diseases= contact dermatitis

Question 6

How does an allergy develop?

Answer 6

• Environmental &/or genetic stimuli
• Barrier dysfunction
• All of above leads to sensitisation
• Leads to changes in T cell sub-sets dominated by Th2
• Causes IgE production
• Forming an allergy

Question 7

Why do we get allergies?

Answer 7

• Components of immune system involved in responses to parasitic infection also involved in allergic response
• System developed to produce rapid tissue-based response
• Lack of infectious drive is a contributory factor in allergic disease

Question 8

Describe the immune response to parasitic disease

Answer 8

• Increase levels of IgE specific to pathogen-cross reactive
• Tissue inflammation with basophil infiltration, eosinophilia & mastocytosis
• Presence of CD4+ T cells secreting IL4, IL5, IL13

Question 9

What is the hygiene hypothesis?

Answer 9

• Stimulation by microbes is protective
• Prevention of autoimmunity by infections
• Pro-biotics in pregnant women
• Mechanism Th1, Th2 deviation

Question 10

What are genetic influences on the ‘allergic’ immune response?

Answer 10

• Polygenic diseases
• Cytokine gene cluster IL3,5,9,13
• IL12R, IL4R
• FCεRI
• IFNγ, TNF
• Not sufficient for disease only susceptibility

Question 11

Define allergen

Answer 11

Antigens that initiate an IgE-mediated response, first encounter results in innate & IgM response

Question 12

What is the conventional immune response?

Answer 12

• Allergen requires processing
• Presentation to T cells & cytokine release
• Resukts in delineation of T-helper subsets into different types

Question 13

How is IgE produced?

Answer 13

• Th2 cell stimulated by IL4 and interaction with B cell

- B cell proliferation producing IgE

Question 14

What are the roles of the Th2 T cell?

Answer 14

• Multiple cytokine release
• Innate inflammatory response
• Drive for immunoglobulin production

Question 15

What diseases are included in the atopic triad?

Answer 15

• Asthma
• Eczema
• Rhinitis

Question 16

Describe rhinitis

Answer 16

• Allergic/non-allergic
• Allergic-perennial/seasonal
• Blocked nose, runny nose, with eye symptoms
• House dust mite, animal danders, pollens
• Treatment- antihistamines & nasal steroids

Question 17

Describe asthma

Answer 17

• Inflammation & hyper-reactivity of small airways
• In childhood aero-allergic stimuli-house dust mite key pathogenic importance
• Immedite symptoms are IgE mediated
• Damage to airways due tolerate phase response
• Damaged airways hyper-reactive to non-allergic stimuli-fumes

Question 18

Describe atopic dermatitis

Answer 18

• Many different types
• Contact- allergic/non-allergic
• Clinically-intense itching, blistering/weeping cracking skin
• House dust mite major trigger
• Topical steroids & moisturisers

Question 19

What is anaphylaxis?

Answer 19

Acute potentially life-threatening IgG mediated systemic hypersensitivity reaction

Question 20

How is an allergy diagnosed?

Answer 20

• History
• Specific IgE
• Skin prick test
• Intra-dermal test
• Oral challenge test- gold standard
• Basophil activation test
• Component resolved diagnostics

Question 21

What are the advantages & disadvantages of Specific IgE?

Answer 21

• A=safe

- D= False negatives/positives

Question 22

What are the advantages & disadvantages of the skin prick test

Answer 22

• A= Quick, pateint satisfaction

- D= False positives/negatives, slight risk, antihistamines

Question 23

What are indications of treatment for allergy?

Answer 23

• Life threatening reactions to wasp & bee sting
• Severe hay fever
• Animal dander allergy

Question 24

What is symptomatic and specific treatment for allergies?

Answer 24

Sym=Antihistamines, Steroids, Adrenaline

Spec= Immunotherapy (submit or sublingual)

Question 25

What are clinical manifestations of food allergies?

Answer 25

- Gastrointestinal: vomiting, diarrhoea, oral symptoms - Respiratory: rhinitis, bronchospasm - Cutaneous: urticaria, angioedema, atopic dermititis - Anaphylaxis