Hypersensitivity

Question 1

What are the 4 types of Gel and Coomb classification?

Answer 1

1 - Immediate hypersenitivity
2 - Direct cell effects
3 - Immune complex mediated
4 - Delayed type hypersensitivity

Question 2

Main antibody in hypersensitivity:

Answer 2

IgE antibody

Question 3

Hygeine hypothesis:

Answer 3

In modern countries, decreased exposure to parasites has left immune system ‘untrained’

Children producing more Th2 more likely to develop allergens than children who switch to producing Th1

Question 4

Vasoactive mediators (2):

Answer 4

Histamine
Tryptase

Question 5

What is an allergen?

Answer 5

When T cells bind to an antigen that catalyses a reaction

Question 6

Sensitisation process (5):

Answer 6

1. Allergen picked up by immune cells in airways
2. Antigen presenting cells migrate to lymph nodes
3. If person is allergic, antigen presenting cells will express costimulatory molecules
4. This results in the production of IgE by B cells
5. Residual IgE antibodies then bind to circulating mast cells via Fc receptors

Question 7

Antigen presenting cells (2):

Answer 7

dendritic cell
macrophages

Question 8

How are TH2 cells made?

Answer 8

Naive T helper cell binds to antigen
Cytokines help T helper cells become TH2

Question 9

Which cytokines help T helper cells become TH2?

Answer 9

Interleukin-4, 5 & 10

Question 10

Which IL’s does TH2 release?

Answer 10

IL4 & IL5

Question 11

What does IL5 stimulate:

Answer 11

Production of eosinophils

Question 12

Mild symptoms of type 1 hypersensitivity (4):

Answer 12

• Hives
• eczema
• allergic rhinitis (hayfever)
• asthma

Question 13

Severe symptoms of type 1 hypersensitivity

Answer 13

Large load of allergen can cause:
→ Inc vascular permeability
→ Airway constriction
→ Can’t supply vital organs
→ ANAPHYLACTIC SHOCK

Question 14

Type 1 second exposure:

Answer 14

Allergen binds to IgE -coated mast cells and basophils causing degranulation

Histamine (mediator) released

Question 15

Early phase reaction (minutes):

Answer 15

Bronchi: smooth muscle contraction; difficulty breathing

Blood vessels: dilation, increase permeability

Release of proteases + eosinophils

Question 16

Late phase reaction (8-12 hours):

Answer 16

TH2 cells, Basophils, Eosinophils recruited to site of allergen

Release of IL-4, IL-5, IL-10

Question 17

Type 2 is mediated by:

Answer 17

Tissue specific antibody to destroy specifc organ or tissue

IgM/IgG

Question 18

Type 2 sensitisation phase:

Answer 18

generation of relevant IgM/IgG antibodies in a classical humoral immune response

Question 19

Type 2 pathological phase:

Answer 19

Mediated by normal antibody effector functions

Question 20

Type 2 lla reaction:

Answer 20

destruction of antigen-positive cells

Question 21

Type 2 llb reaction:

Answer 21

stimulation of cell surfaces antigens

Question 22

What happens when too many antibodies bind to receptors? (Type 2)

Answer 22

An increase in thyroid hormone production

Question 23

Type 3:

Answer 23

Mediated by soluble immune complexes

1. Large amounts of antigen-antibody complex not removed by macrophages
2. Complexes lodge in capillaries
3. Classical complement pathway activated leading to vasodilation and cell death
4. Neutrophils are attracted to the area
5. Neutrophils discharge killing antigens causing huge inflammation

Question 24

Type 4 is mediated by:

Answer 24

T cells

Question 25

How is type 4 driven by CD4+ T cells?

Answer 25

Activation of CD4+ T cells leads to proliferation and inc. in macrophage recruitment and activation

Question 26

Hallmarks of type 4:

Answer 26

large number of macrophages at reaction site

takes 24-48 hours for symptoms to manifest

garnulomas often form due to infectious pathogens which cannot be cleared