IMMUNOLOGY

Question 1

Type 1 hypersensivity

Answer 1

IgE mediated, seconds to minutes
Allergen binds to IgE on basophils/mast cells –> x-linkage –> degranulation
Vasoactive amines (histamine, tyrptase, leukotrienes, PG, PAF) –> inflammatory response (INF/TNF/GMCSF)

Question 2

Type 2 hypersensitivity

Answer 2

Antibody-dependent cytoxic, mintures to hours with IgG/M/A attacking antigens on cell surface
Complement, lysis and opsonisation
E.g AI haemolytic anaemia, goodpastures, blood transfusion reaction, myasthenia gravis, graves

Question 3

Type 3 hypersensitivity

Answer 3

Immune complex mediated, 1-3 weeks, duration 10-15hrs
IgG/M form Ag/Ab complexes depositing beneath endothelium/tissues –> activation of complement triggering neutrophils with tissue destruction & anaphylotoxins
E.g. SLE, GN, HSP, serum-sickness like reaction

Question 4

Type 4 hypersensitivity (delayed)

Answer 4

Cell mediated, days to weeks with previous exposure
APCs display antigens on T helper cells –> cytokine/interferon release –> macrophage/Tc cell activation
E.g. TB skin reactions, GVHD, contact dermatitis, SJS/TENS

Question 5

Atopy substances involved

Answer 5

Th2 cytokines
- Il4, IL13 –> isotype switch to IgE
- IL5, IL 9 –> differentiation/development of eosinophils
- IL 3, IL4, IL9 –> mast cell activation

Question 6

Atopic dermatitis/asthma substances in addition to regular cytokines

Answer 6

Th1 cells –> interferon gamma and TNF
Chronic allergy–> Th1 releases IL17 –> acts on epithelial cells and APCs to cause a proinflammatory state

Question 7

Inhibitors of IgE synthesis

Answer 7

IL12, interferon alpha and gamma

Question 8

Th2 cytokines inducing tissue remodelling

Answer 8

IL4/9/13: mucous hypersecretion and metaplasia of mucous cells
IL4/13: fibroblast growth
IL5/9: subepithelial fibrosis

Question 9

Differentials of eosinophilia (6 categories)

Answer 9

• Allergic disease – atopic conditions
• Respiratory – eosinophilic pneumonia, ABPA
• GIT – eosinophilic gastroenteritis, allergic colitis, IBD
• Infections – helminthic infection
• Neoplastic – eosinophilic leukemia, Hodgkin disease
• Drug induced

Question 10

Differentials of high IgE (at least 4)

Answer 10

• Allergic disease – atopic conditions (eczema most common)
• Helminthic infection
• Hyper IgE syndrome
• Allergic bronchopulmonary aspergillosis
• Wiskott/Aldrich syndrome
• Bone marrow transplant
• Hodgkin disease
• Bullous pemphigoid
• Idiopathic nephritic syndrome

Question 11

Medications to withhold when doing SPT

Answer 11

Antihistamine (2nd gen ~4 days, H2 antagonists e.g. ranitidine and cimetidine 1 day), antidepressants (7 days for TCAs and mirtazapine), Sanomigraine, prochlorperazine, some neuroleptics for up to 2 weeks (olanzapine, quetiapine, chlorpromazine, fluenthixol/phenazine)

Question 12

Medications which do not affect SPT

Answer 12

leukotrient receptor antagonists (e.g. singulair), decongestants, SABA/LABA, glucocorticoids, oral theophylline, cyclosporine