Relate types of hypersensitivity to the root biological cause
Introduction:
The immune response is a protective process but sometimes can be harmful to the host. Hypersensitivity is the condition in which an immune response results in an excessive reaction that leads to tissue damage, disease, or can even be fatal in the sensitized host.
Hypersensitivity occurs in individuals who have had prior contact with the allergen (antigen). The initial contact sensitizes the immune system by priming appropriate B or T cells. This is referred to as 'sensitizing' or the 'priming' dose. Subsequent contact with similar antigen results in hypersensitivity, and the dose is referred to as a 'shocking' dose.
Answer:
Hypersensitivity reactions can be of the following four types:
- Type I (Anaphylactic)
- Type II (Cytotoxic)
- Type III (Immune complex)
- Type IV (Cell-mediated or Delayed)
Type-I, II, and III hypersensitivity reactions are the acute or subacute (immediate) reactions, whereas the Type-IV hypersensitivity reaction is a delayed-type. Type I, II, and III appears and recedes quickly, whereas the type-IV appears slowly (in about 24 to 72 hours) and is long-lasting.
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