Hypersensitivity

Question 1

What is hypersensitivity ?

Answer 1

The antigen specific immune responses that are either inappropriate or excessive and result in harm to host

Question 2

What are the different types of triggers of hypersensitivity ?

Answer 2

Exogenous antigens (drugs,infectious microbes , non infectious substances )

Intrinsic antigens (self)

Question 3

What are the type of hypersensitivity reactions that are antibody mediated ?

Answer 3

Type I, II and III

Question 4

What are the two phases of hypersensitivity reaction?

Answer 4

Sensitisation phase and effector phase

Question 5

What is the sensitisation phase of the hypersensitivity reaction ?

Answer 5

First encounter with the antigen , activation of APCs and memory cells

Question 6

What is the effector phase of the hypersensitivity reaction ?

Answer 6

Pathological reaction upon reexposure to the same antigen and activation of the memory cells

Question 7

Which antigens are targeted in type II ?

Answer 7

Cell bound antigens
Endogenous : self
Exogenous : blood group antigens, rhesus D antigens

Question 8

How does type II reactions cause tissue/cell damage ?

Answer 8

• Complement activation : cell lysis(MAC), neutrophil recruitment (C3a,C5a chemoattractant), opsonisation (C3b)
• AB dependent cell cytotoxicity (Natural killer cell bind to AB )

Question 9

Give two eg of Type II reactions induced diseases with exogenous antigens ?

Answer 9

Haemolytic disease of the newborn (rhesus D)
Transfusion reactions (A/B antigens )

Question 10

Give eg of diseases caused by type II reaction to self antigen ?

Answer 10

Autoimmune haemolytic anaemia
Immune thrombocytopenia
Goodpasture’s syndrome (basement membrane of kidney )

Question 11

Which Ig can pass through the placenta ?

Answer 11

IgG

Question 12

Other than tissue damage , what can type II reaction cause ? Give disease eg

Answer 12

Receptor stimulation : Graves’

Receptor blockade : Myasthenia gravis

Question 13

What are the therapeutic approaches to type II reactions ?

Answer 13

Immune suppression (prednisolone, anti metabolite )
Plasmapheresis(circulating ab)
Splenectomy 
IV Ig 
Correct metabolism 
Replacement therapy

Question 14

Type III hypersensitivity reactions target which antigens ?

Answer 14

Soluble , foreign (infection) and Endogenous

Question 15

How does type III reactions cause tissue damage ?

Answer 15

By immune complex deposition

Question 16

Why would immuno complex deposit in the tissue ?

Answer 16

Size of complex : intermediate
Low affinity antibody
Complement deficiency(C3b)
Local tissue factors (haemodynamic, physicochemical )

Question 17

How does immuno complex deposition cause tissue damage ?

Answer 17

Activates complement , neutrophil chemotaxis , neutrophil adherence and degranulation

Question 18

Give 3 eg of diseases caused by type III reaction and their antigens

Answer 18

Rheumatoid arthritis(self antigen  Anti-Rheumatoid factor ) 
Glomerulonephritis (infectious : Hep B , Bacterial endocarditis)
Systemic lupus erythemtosus (Ds-DNA)

Question 19

What is the mechanism of action in type IV hypersensitivity reaction ?

Answer 19

Cell mediated , involves lymphocytes and macrophages

Sensitisation activates TH1 which activates macrophages in effector phase releasing a lot of cytokines

Question 20

What are the subtypes of type IV reaction ?

Answer 20

Contact (48-72hr, epidermis , eczema )
Tuberculin (48-72hr, dermal reaction ,swelling)
Granulomatous (21-48 days, persistent infection )

Question 21

Give eg of autoimmune diseases caused by type IV reaction

Answer 21

Insulin dependant diabetes : pancreatic islet cells targeting

Hashimoto’s thyroiditis : CD8 T cells and AB so type IV and II

Question 22

Give eg of therapies for type III and IV reactions

Answer 22

Anti inflammatory drugs : non steroidal, oral prednisolone , azathioprine, cyclophosphamide

Monoclonal antibody : against B cells , T cells , APCs, Cytokines