hypersensitivity reactions

Question 1

what is type 1 hypersensitivity?

Answer 1

IgE mediated
most common and rapid
mild to life threatening

Question 2

role of IgE in type 1 hypersensitivity?

Answer 2

• B cells activated during sensitisation
• IgE binds to Fc receptor on mast cells or CD63 on basophils
• IgE recognises allergen and binds rapidly at next exposure

Question 3

examples of type 1 hypersensitivity?

Answer 3

atopic eczema (dermatitis)
urticaria (hives)
systemic anaphylaxis
penicillin allergy

Question 4

how to test for type 1 hypersensitivity?

Answer 4

skin prick
blood test
patch test
food challenge

Question 5

what is type 2 hypersensitivity?

Answer 5

non-IgE (cytotoxic)
activation of complement by IgG or IgM

Question 6

what is the cell lysed by in type 2 hypersensitivity?

Answer 6

membrane attack complex (complement)
antibody dependent cell mediated cytotoxicity (NK cells)

Question 7

example of type 2 hypersensitivity reaction?

Answer 7

haemolytic anaemia

Question 8

what is type 3 hypersensitivity?

Answer 8

reactions against soluble antigens in serum
1) deposition of antibody-antigen aggregates
2) complexes activate complement

Question 9

examples of type 3 hypersensitivity?

Answer 9

arthus reaction
serum sickness
oral erythema multiforme

Question 10

what is type 4 hypersensitivity?

Answer 10

• T cell response to foreign or modified self proteins
• delayed response - time to recruit t cells
• localised t cell reaction at site of encounter