Hypersensitivity Reactions

Question 1

Describe hypersensitivity.

Answer 1

-excessive harmful reactions made by the normal immune system
-require pre-sensitized (immune) state of the host

Question 2

Describe the Gell & Coombs classification.

Answer 2

1. Type 1 = immediate hypersensitivity reactions
   -IgE - histamine release + other mediators from mast cells & basophils
2. Type 2 = cytotoxic hypersensitivity reactions
   -IgG or IgM antibodies bound to cell surface antigens -complement fixation
3. Type 3 = immune complex reactions
   -circulating antigen-antibody immune complexes that deposit in postcapillary venules
   -complement fixation
4. Type 4 = delayed hypersensitivity reaction (cell mediated)
   -mediated by T cells rather than antibodies