Hypersensitivity

Question 1

What are type I hypersensitivity reactions?

Answer 1

Allergies

IgE mediated

Question 2

What are type I hypersensitivity reaction set off by?

Answer 2

Genetically hypersensitive T helper cells

Question 3

What are the phases of type I hypersensitivity?

Answer 3

Sensitisation

Reaction

Question 4

What happens in the sensitisation phase of type I hypersensitivity?

Answer 4

Antigen presenting cell picks up allergen, and is met by T helper cell, causing an aggressive reaction and release of IL-4 and IL-5
IL-4 activates IgE cells and IL-5 activates granulocytes
IgE gets picked by by mast cells and primes it

Question 5

What happens in the reaction phase of type I hypersensitivity?

Answer 5

Re-exposure to antigen triggers fast degranulation of primed mast cells, which release histamine and cause inflammation
Release of interleukins cause activation of eosinophils and T helper cells, causing more inflammation and more priming of mast cells

Question 6

How can allergies be tested for?

Answer 6

Skin testing
Patch testing
Serum tryptase

Question 7

What is the treatment of allergies?

Answer 7

Antihistamines
Corticosteroids
Adrenaline
Allergen avoidance

Question 8

What is atopy?

Answer 8

Genetic tendency to developing allergies

Question 9

What are the 3 atopies?

Answer 9

Hayfever
Asthma
Eczema

Question 10

What is eczema?

Answer 10

Degranulation of basophils and mast cells in response to sensitised IgE
Leaky skin allows mire allergen in and water out

Question 11

What is type II hypersensitivity?

Answer 11

Cytotoxic hypersensitivity

Tissue specific

Question 12

What is the process of type II hypersensitivity?

Answer 12

Failure of central tolerance allows self reactive B and T cells into bloodstream, which produce IgE against normal self cells
Anti-body antigen complexes form and oponise the reactant cell, and complement system and macrophages are activated
NK cells respond to oponisation and degranulate

Question 13

What is type III hypersensitivity?

Answer 13

Immune complex mediated

Systemic

Question 14

What is the process of type III hypersensitivity?

Answer 14

Plasma cell and T helper cell form ligand bond, and antibodies release
Antigen-antibody complexes form and are deposited in tissues, causing inflammation

Question 15

What is an example of a type III hypersensitivity?

Answer 15

Systemic lupus erythematous

Question 16

What causes systemic lupus erythematous?

Answer 16

Failure of central tolerance allowing self reactive B and T cells to circulate
leaked auto-antigen presented to B cells, passed to T helper cells, and antibodies against DNA are made

Question 17

What are type IV hypersensitivity reactions?

Answer 17

Delayed hypersensitivity

T cell mediated

Question 18

Why are type IV hypersensitivity reactions delayed?

Answer 18

Takes 48-72 hours as it takes time to recruit T helper cells

Question 19

What is the process of a type IV hypersensitivity reaction?

Answer 19

Antigen presenting cells present antigen to T helper cell, which binds with it
IL-12 is released by APC and differentiates T helper cell to TH1
TH1 cell then releases IL-2, proliferating other TH1 cells, and IFN-gamma activating macrophages
Macrophages release proinflammator cytokines