L20: Hypersensitivity

Question 1

what are hypersensitivity diseases

Answer 1

diseases caused by the immune response

Question 2

when responses are not adequately controlled or
targeting to ____ then the immune response
becomes ____

Answer 2

the wrong tissue, the cause of the disease

Question 3

Type 1 mediated

Answer 3

IgE - allergy

Question 4

Type II mediated

Answer 4

IgG - antibody mediated (cytotoxic)

Question 5

Type III mediated

Answer 5

IgG - immune complex

Question 6

Type IV mediated

Answer 6

TH cells

Question 7

Why do we have IgE responses?

Answer 7

crucial in defence against parasite infection

Question 8

Why IgE and not IgG/FcR mediated for T1HS

Answer 8

• Normal IgG/FcR-mediated activity not very effective in mobilising fast response
• The mast cell receptor affinity for IgE is high and the IgE/FcR response is immediate in the presence of pathogen

Question 9

What is the action of IgE

Answer 9

causes mast cell degranulation by binding to FcER receptor and antigen crosslinking IgE

Question 10

what happens when mast cells degranulate?

Answer 10

release of mediators
1. chemoattractants
2. activators (blood flow/dilation)
3. spasmogens (smooth muscle contraction, mucous secretions)

Question 11

Mast cell mediators that are synthesised after activation

Answer 11

lipid mediatiors, cytokines

Question 12

mast cell mediators pre-formed, what does this mean?

Answer 12

• biogenic amines (histamines), enzymes (tryptases)
• immediate release upon activation

Question 13

action of histamines

Answer 13

vasodilation and vascular leak

Question 14

action of enzymes

Answer 14

tissue damage

Question 15

action of lipid mediators

Answer 15

bronchoconstriction, intestinal hypermotility, inflammation

Question 16

action of cytokines

Answer 16

inflammation

Question 17

common causes of allergies

Answer 17

rhinitis (hay fever), insect stings, food allergies, small molecules (morphine)

Question 18

What is mast cell sensitization

Answer 18

The binding of IgE to its high-affinity IgE receptor on mast cell surfaces upon first exposure to allergen

Question 19

What happens upon re-exposure when a mast cell has been sensitized?

Answer 19

mast cell preloaded with IgE - triggering a HS reaction

Question 20

allergies treatment

Answer 20

1. avoidance
2. antihistamines (bind histamine receptor so histamine cant trigger symptoms)
3. coritcosteroids
4. epinephrine
5. desensitisation (gradually increasing dose of allergen to insude high affinity IgG - competes with IgE = stops allergic reaction)

Question 21

allergy testing

Answer 21

immunoassay (test for AB to allergen), skin prick

Question 22

Explain the hygiene hypothesis in terms of T helper cells

Answer 22

Immune response to common allergens get polarised away from having a Treg/Th1 response to a Th2 IgE response

Question 23

Explain what happens in T2 HS

Answer 23

• Antibodies (IgG/IgM) bind directly to antigens on the surface of cells and cause lysis
• can attack mobile cells (in blood stream), or antibodies bind fixed/solid tissue

Question 24

what is hemolytic anemia

Answer 24

Individual makes
antibodies to their own red
blood cells (RBC)

Question 25

Explain how hemolytic anemia occurs

Answer 25

• IgG coated RBC are cleared from circulation via uptake by Fc receptor bearing macrophages
• IgM coated RBC are fixed by complement and directly lysed (MAC complex formation)

Question 26

What happens when AB bind to self antigen on tissue (T2 HS)

Answer 26

1. ADCC - antibody dependent cellular cytotoxicity
2. complement activation
3. frustrated phagocytosis

Question 27

what is an example of Anti-tissue antibodies

Answer 27

goodpastueres syndrome

Question 28

explain how goodpastures syndrome occurs

Answer 28

• Antibodies against type IV collagen in glomerular basement membrane
• Affects the kidney glomeruli and the alveoli in the lungs
• Antibodies trigger complement activation that damages epithelial cells
• Patients present with transient kidney dysfunction and bleeding in the lungs

Question 29

explain what happenscin T III HS

Answer 29

• Antibody complex is not cleared
• Complex becomes large, insoluble
• Complexes lodge in sites and provoke an immune response

Question 30

give examples of T III HS

Answer 30

serum sickness, rheumatoid arthritis

Question 31

What is Txpe IV HS

Answer 31

delayed-type hypersensitvity

Question 32

Type IV HS is mediated by?

Answer 32

antigen specific T-cells

Question 33

Explain how TIV HS is established

Answer 33

Antigen injected, process by local APC, Th1 effector response, recruitment of phagocytes, inflammation at site

Question 34

What are examples of T IV HS

Answer 34

contact sensitivity eg jewellery

Question 35

explain the process of contact sensitivity

Answer 35

• normal proteins act as carrier for small molecule
• transport to lymph