Hypersenstivity

Question 1

What is hypersensitivity?

Answer 1

Hypersensitivity is an exaggerated, inappropriate adaptive response. Happens due to the accumulation of antigens and usually caused on secondary exposure of them.

Question 2

What hypersensitivity reactions are there

Answer 2

Type I,II,III- antibody meditated

Type IV- T cell and macrophage related

Question 3

What is a type 1 hypersensitivity?

Answer 3

This is an IgE response to inoncuous environmental antigens- IgE binds to the Fc receptor on the mast cell and a second encounter causes inflammatory mediators. It causes an acute inflammatory reaction- asthma, rhinos

Question 4

What are the treatments for hypersensitivity

Answer 4

Avoidance
Sodium chromoglycate- stabilises mast cells
Anti-histamines
Desensitisation

Question 5

What is anaphylactic shock?

Answer 5

Severe type 1 reaction that causes systemic symptoms- these include wheezing, face swelling, larynopharynx, nausea, dizziness, fainting, low blood pressure.

Note: Dentists can cause type 1 reaction to anaesthetics- therefore must have adrenaline nearby.

Question 6

What is the type 2 hypersensitivity reaction called

Answer 6

Antibody- dependent cytotoxic hypersensitivity

Question 7

What occurs in type 2

Answer 7

Antibody- dependent cytotoxic hypersensitivity- 12-18 hours after antigen exposure and it causes IgG/IgM to bind to either the foreign or self antigen and allows phagocytosis to happen to those identified cells.

Question 8

What are the examples of type 2

Answer 8

Blood transfusion- incompatible blood causes fever, hypotension, nausea, vomiting

Haemolytic diesease of the newborn- suppose the mother is rhesus -ve and the fetus is rhesus postive- the mother becomes sensitised to the rhesus positive antigen and therefore a subsequent pregnancy with a rhesus positive baby can lead to a immunological reaction from the foetus.

Treated with anti-RHD iGg- eliminates all Rhd- positive RBC before immune response occurs.

Question 9

What is type 3 hypersenstivity?

Answer 9

This occurs more slowly between 18-24 hours. It is medicated by persistence and deposition of antigen- antibody complexes. It can cause severe inflammation
Influenced by

1) size of IC
2) route of antigen
3) dose of antigen
4) binding of antigen to tissue

Question 10

What is a type 4 hypersensitivity?

Answer 10

Delayed reaction occurs between 48-72 hours of exposure. There are three types:

1) contact- eczematous reaction to silver- common with nickel, chromate
2) tuberculin - skin swelling develops after intradermal exposure e.g. seen with a tuberculin infiltration
3) granulomatous- granula formation- aggregation and proliferation of macrophages persisting for weeks.

Type 4 hypersensitivity is medidated by T cells and macrophages.

They have two phases:

1) sensitisation- Silver encountered by dendritic cell in the skin and this migrates to the lymph node and presents the Ag to the T cell
2) elicitation- Silver encountered again and memory T cells are triggered which causes inflammation.