Hypersensitivity

Question 1

What are different types of acquired immunity?

Answer 1

1. Antibody response - humoral

2. Cell-mediated response

Question 2

Describe ab response?

Answer 2

Occur quickly - systemic and widespread (ab soluble protein)

1. Ag uptake
2. APC process - present Ag B cells
3. T cell - release cytokines
4. B cell clonal expansion - diff plasma cells
5. Ab production

Question 3

Describe cell mediated response?

Answer 3

1st exposure

• Ag processed - presented to naive T cell via MHC
• T cell prolif - Ag specific memory cell

2nd exposure

• T cell recognise Ag - release cytokines
• Targeted apoptosis

Question 4

What is hypersensitivity?

Answer 4

When immune system respond in exaggerated/ inappropriate way
Usually 2nd response
Type 1-3 - ab mediated
Type 4 - cell mediated

Question 5

Type I Hypersensitivity?

Answer 5

Immediate/ anaphylaxis

Acute hypersensitivity w/ rapid onset - IgE mediated

Question 6

What cells are involved type I hyper?

Answer 6

1st exposure - IgE made

2nd exposure - Ag bind Fc receptor on mast cell - cause histamine release and IL5

Question 7

What does IL5 and histamine release cause?

Answer 7

IL5 -esoinophil release

Histamine; vascular dilation, increased vascular permeability, oedema, bronchospasm, urticarial rash

Question 8

Diagnosis of type I?

Answer 8

Wheel and flare
Wheel - caused extravasation of serum = angio-oedema
Flare - redness caused by axon response

Question 9

Management Type I?

Answer 9

Adrenaline
Antihistamine
Corticosteroid
Avoidance

Question 10

What is type II hypersensitivity?

Answer 10

Cytotoxic reaction

Ab target cell surface self-ag = autoantibody

Question 11

Mechanism type II?

Answer 11

Ab target autoantibody

Important

• Acute transplant rejection/ blood transfusion
• Haemolytic disease of new born

Question 12

Type II - pregnancy and foetal blood?

Answer 12

• 1st preg - baby RhD+ - foetal blood enter circulation - baby born but raised ab to RhD+
• 2nd preg - if baby Rhd+ - IgG cross placenta and destroy foetal erythrocytes
• Preformed ant-RhD given Rhd - mother after birth

Question 13

Difference between pemphigus and phemigoid?

Answer 13

Type II

Pemphigus - autoab against desmoglein 1+3 - prevent formation of gap junction = epithelial shed (Esp mucosa)

Pemphigoid - autoab against hemidesmosomes - prevent binding epithelium w/ dermis at basement membrane - epithelial shed at skin and mucosa

Question 14

Type III hypersensitivity?

Answer 14

Immune complex between Ab/Ag in serum
Complex deposits in lining blood vessel, glomeruli and lungs
Cause: complement activation, leukocyte binding and inflammation

Question 15

Mechanism type III?

Answer 15

1. Immune complex usually bind c’ - bind to erythrocyte and remodelled in liver
2. Inflammation - complex bind in lining
3. Become activated = histamine release
4. Increase vascular permeability - further deposition
5. Cause platelet aggregation
6. Lysomal enzyme - further tissue damage

Question 16

What is type III important in?

Answer 16

SLE, eryhtema multi-frome

Question 17

What is type IV hypersensitivity?

Answer 17

Delayed reaction which is cell mediated - slow to develop and slow to resolve

1. T cell recognise Ag expressed
2. Cytokine release

Question 18

What is type IV hypersensitivity important in?

Answer 18

1. Lichenoid reaction

2. Contact dermatitis

Question 19

Mechanism type IV?

Answer 19

Ag in skin internalised by langerhan cells
Travel lymph node - present Ag to T cell
Form memory CD4 cells

Elicitation Phase

• Langerhans cell move from epidermis - dermis
• Present Ag to memory cell
• Cause secretion and pro-inflame cytokines
• Increased leukocyte attraction and neutrophil
• Tissue damage due cytokines