Compare and contrast type I hypersensitivity with type IV hypersensitivity with respect to reaction time, mediators, and cells involved
What will be an ideal response?
Type I (immediate) hypersensitivity is very quick. The reaction time can be seconds to minutes after exposure to the allergen. This type of hypersensitivity starts with a prior sensitization to the allergen during which IgE specific for the allergen is produced. The IgE that is made binds to mast cells, basophils, and eosinophils. The response can be either local or systemic and is due to a subsequent exposure to the allergen. Upon subsequent exposure, the allergen binds to the IgE on mast cells, basophils, and eosinophils, causing them to degranulate and release a variety of inflammatory molecules, including histamines, kinins, proteases, leukotrienes, and prostaglandins.
Type IV (delayed or cell-mediated) hypersensitivity has a much slower reaction time. It takes 12-24 hours to start developing. Antigen does not bind to antibody; it binds to antigen-presenting cells and T cells. As with type I, a type IV response is due to a prior exposure, but in the case of the type IV hypersensitivity, memory T cells are produced. In both type I and type IV hypersensitivities, inflammation is a common result.
Bloom's Taxonomy: Analysis
Section: Hypersensitivities
Learning Outcome: 18.1
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