Hypersensitivity

Question 1

What is hypersensitivity?

Answer 1

condition where normally protective immune system has harmful effects on body

Question 2

What is type 1 hypersensitivity?

Answer 2

Mediated by specific IgE antibodies e.g. asthma, allergic rhinitis
Most diseases thought of as an allergy is likely type 1 hypersensitivity

Question 3

What is type 1 hypersensitivity also know as?

Answer 3

Anaphylactic hypersensitivity

Wheal and Flare

Question 4

How does type 1 hypersensitivity relate to allergy?

Answer 4

Its an allergic reaction de to re-exposure to an antigen
1st allergen exposure= sensitisation
2nd exposure = allergic reaction

Question 5

How does type 1 hypersensitivity work?

Answer 5

1. Allergens presented by B cell
2. Th2 cell binds to antigen presenting cell- releases IL-4, IL-12 (cytokines)
3. Plasma cells and memory cells produced
4. Plasma cells can produce specific IgE
5. IgE bonds to sensitized mast cells
6. Mast cells secrete histamine, heparin, proteases etc. after degranulation after re-exposure to allergen- further Th2 differentiation

Question 6

What are the different phases of type 1 hypersensitivity?

Answer 6

Early Phase: mast cells only
Later Phase: recruitment of early inflammatory cells
Late Phase: recruitment of eosinophils and Th2 cells

Question 7

What is type 2 hypersensitivity?

Answer 7

Destruction of cells by IgG or IgM bound to cell surface antigens- inflammation and tissue damage

Question 8

What can cause type 2 hypersensitivity?

Answer 8

Mismatching of blood transfusion, haemolytic disease of newborn, immune thrombocytopenia, grave’s disease

Question 9

What is type 2 hypersensitivity also called?

Answer 9

Antibody- mediated cytotoxic hypersensitivity

Question 10

How does type 2 hypersensitivity work?

Answer 10

Mechanism 1: anti-receptor activity: receptor blockage or activation
Mechanism 2: classical activation of complement cascade
Mechanism 3: antibody dependent cell mediated cytotoxicity

Question 11

What is type 3 hypersensitivity?

Answer 11

Immune complex deposited (in cell walls and tissues) promoting inflammation and tissue damage
Attracts neutrophils which degranulate if they can’t phagocytose

Question 12

What is an immune complex?

Answer 12

non cell bound antigen-antibody complex which is normally cleared by immune system

Question 13

What is type 3 hypersensitivity also known as?

Answer 13

Immune complex driven disease

Question 14

What are symptoms of type 3 hypersensitivity?

Answer 14

Rash
Fever
Joint Pain
Vasculitis
Glomerulonephritis
Arthritis

Question 15

What immune diseases are involved in type 3 reactions?

Answer 15

Rheumatoid arthritis
Multiple sclerosis
Systemic Lupus Erythematosus (SLE)- IgG’s against DNA or proteins in nucleus which form persistent immune-complex deposits

Question 16

What causes type 3 hypersensitivity?

Answer 16

Diseases develops from autoimmune origin encounters with foreign antigens e.g. persistent infections

Question 17

What is type 4 hypersensitivity?

Answer 17

T cell mediated
Its a delayed type hypersensitivity
Sensitisation phase needs to occur where antigen is presented to naive T cell

Question 18

What is type 4 hypersensitivity also known as?

Answer 18

delayed type or T cell mediated hypersensitivity

Question 19

How does type 4 hypersensitivity work?

Answer 19

Th cell binds to dendritic cell
Dendritic cell secretes IL-12 which makes Th cell into Th1 cell
Th1 cell secretes IL-2, IFN gamma- results in Th cell proliferation and macrophages

Question 20

What happens in type 4 hypersensitivity on exposure to antigen?

Answer 20

Memory cells promote inflammation at site of exposure however there’s a delay because memory T cells respond slower

Question 21

What are examples of type 4 hypersensitivity?

Answer 21

Contact dermatitis (e.g. in poison ivy, hapten drives TH1 response), asthma (by Th2), graft tissue rejection

Question 22

What is a hapten?

Answer 22

Small molecule which causes an immune response when attached to larger carrier such as protein
E.g. in poison ivy expose, uruhsiol is the hapten

Question 23

Through what mechanisms does an antibody result in disease in type II hypersensitivity?

Answer 23

Anti-receptor activity: blocking or activating its function
Antibody dependent cell-mediated cytotoxicity
Classical activation of compliment cascade

Question 24

What is the result of compliment pathway activation?

Answer 24

Antibody on cell surface is recognised by compliment components
This leads to formation of MAC on surface of cell and cell death due to loss of osmotic integrity
Activation of compliment pathways results in inflammation, opsonisation and recruitment and activation of immune cells

Question 25

What occurs in antibody dependent cell-mediated cytotoxicity?

Answer 25

Antibody- antigen complex on surface of cells are bound by Fc receptors expressed by cells such as granulocytes and NK cells. This leads to direct lysis of the target cell but also the release of inflammatory mediators, chemokines and cytokines

Question 26

How does serum sickness cause type III hypersensitivity?

Answer 26

Person is bitten by snake
They may be given anti-venom
These are foreign proteins and while neutralise venom, our body creates antibodies that recognise anti-venom
If person gets bitten again antibodies will quickly recognise anti-serum and drive rapid inflammation