Hypersensitivity
The same immune reactions that protect us from infection can also inflict a great deal of damage, not simply on a pathogen, but on our own Cells and tissues.
Richet coind the term 'Anaphylaxis' derived from the Greek and translated loosely as "against protection" to describe this overreaction of the immune system, the description of a hypersensitivity.
Two immunologist, P.G.H Gell and R.R.A. Coombs proposed a classification scheme to discriminate among the various types of hypersensitivity -
Type-1 hypersensitivity -
type-1 hypersensitivity reactions are mediated by IgE -antibodies and include many of the most common allergies to respiratory allergens, such as Pollen and Dust mites.
Type-2 hypersensitivity -
Type-2 hypersensitivity reactions results from the binding of IgG or IgM to the surface of host Cells, which are then destroyed by complement or cell mediated mechanism.
Type-3 hypersensitivity -
In type-3 hypersensitivity reactions, antigen - antibody complexes deposited on host Cells induce complement fixation and an ensuing inflammatory response.
Type-4 hypersensitivity -
Type-4 hypersensitivity reactions result from inappropriate T- Cell activation.
In general, type-1, type-2 and type-3 hypersensitivity comes under the immediate hypersensitivity results from antigen - antibody reactions, and type-4 hypersensitivity under the delayed type hypersensitivity caused by inappropriate T- Cell activation.
