Hypersensitivity

Question 2

What is the Gell and Coombs classification?

Answer 2

A system dividing hypersensitivity reactions into Types I–IV based on mechanism; Type V has since been added for receptor-mediated antibody effects.

Question 3

What is the mechanism of Type I hypersensitivity?

Answer 3

Antigen reacts with IgE bound to mast cells causing mast cell degranulation.

Question 4

What are examples of Type I hypersensitivity reactions?

Answer 4

Anaphylaxis, atopy including asthma, eczema and hay fever.

Question 5

What is the mechanism of Type II hypersensitivity?

Answer 5

IgG or IgM antibodies bind to antigens on cell surfaces causing cell destruction or dysfunction.

Question 6

What are examples of Type II hypersensitivity?

Answer 6

Autoimmune haemolytic anaemia, ITP, Goodpasture’s syndrome, pernicious anaemia, acute haemolytic transfusion reactions, rheumatic fever, pemphigus vulgaris and bullous pemphigoid.

Question 7

What is the mechanism of Type III hypersensitivity?

Answer 7

Immune complex formation between free antigen and antibody (usually IgG or IgA), depositing in tissues and causing inflammation.

Question 8

What are examples of Type III hypersensitivity?

Answer 8

Serum sickness, systemic lupus erythematosus, post-streptococcal glomerulonephritis, hypersensitivity pneumonitis (acute phase), Arthus reaction after vaccination.

Question 9

What is the mechanism of Type IV hypersensitivity?

Answer 9

T-cell mediated delayed immune response.

Question 10

What are examples of Type IV hypersensitivity?

Answer 10

Tuberculosis/tuberculin skin reaction, graft versus host disease, allergic contact dermatitis, scabies, extrinsic allergic alveolitis (chronic phase), multiple sclerosis, Guillain-Barré syndrome.

Question 11

What is the mechanism of Type V hypersensitivity?

Answer 11

Antibodies bind to cell surface receptors, stimulating them or blocking ligand binding.

Question 12

What are examples of Type V hypersensitivity?

Answer 12

Graves’ disease and myasthenia gravis.