What are different types of acquired immunity?
- Antibody response - humoral
2. Cell-mediated response
Describe ab response?
Occur quickly - systemic and widespread (ab soluble protein)
- Ag uptake
- APC process - present Ag B cells
- T cell - release cytokines
- B cell clonal expansion - diff plasma cells
- Ab production
Describe cell mediated response?
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
What is hypersensitivity?
When immune system respond in exaggerated/ inappropriate way
Usually 2nd response
Type 1-3 - ab mediated
Type 4 - cell mediated
Type I Hypersensitivity?
Immediate/ anaphylaxis
Acute hypersensitivity w/ rapid onset - IgE mediated
What cells are involved type I hyper?
1st exposure - IgE made
2nd exposure - Ag bind Fc receptor on mast cell - cause histamine release and IL5
What does IL5 and histamine release cause?
IL5 -esoinophil release
Histamine; vascular dilation, increased vascular permeability, oedema, bronchospasm, urticarial rash
Diagnosis of type I?
Wheel and flare
Wheel - caused extravasation of serum = angio-oedema
Flare - redness caused by axon response
Management Type I?
Adrenaline
Antihistamine
Corticosteroid
Avoidance
What is type II hypersensitivity?
Cytotoxic reaction
Ab target cell surface self-ag = autoantibody
Mechanism type II?
Ab target autoantibody
Important
- Acute transplant rejection/ blood transfusion
- Haemolytic disease of new born
Type II - pregnancy and foetal blood?
- 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
Difference between pemphigus and phemigoid?
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
Type III hypersensitivity?
Immune complex between Ab/Ag in serum
Complex deposits in lining blood vessel, glomeruli and lungs
Cause: complement activation, leukocyte binding and inflammation
Mechanism type III?
- Immune complex usually bind c’ - bind to erythrocyte and remodelled in liver
- Inflammation - complex bind in lining
- Become activated = histamine release
- Increase vascular permeability - further deposition
- Cause platelet aggregation
- Lysomal enzyme - further tissue damage
What is type III important in?
SLE, eryhtema multi-frome
What is type IV hypersensitivity?
Delayed reaction which is cell mediated - slow to develop and slow to resolve
- T cell recognise Ag expressed
- Cytokine release
What is type IV hypersensitivity important in?
- Lichenoid reaction
2. Contact dermatitis
Mechanism type IV?
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
