Atopy in hypersensitivity is -
Type I hypersensitivity occurs in two forms :
1. Anaphylaxis
2. Atopv
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Acute, potentially fatal, systemic.
Chronic. Nonfatal. Localized.
Remember
 Mast cells are the most important cells in type 1 hypersensitivity.
O Eosinophils are the most important cells in the late phase reaction of type I hypersensitivity,
 Histamine is the most important mediator in type 1 hypersensitivity.
 1L-4 is particularly important, it is essential for turning on IgE secreening B cells.
 PAF is the most important cytokine in the initiation of late phase reaction.
Most potent eosinophilic activating cytokine is 1L-5.
Systemic type I hypersensitivity
Systemic type II hypersensitivity
Local type I hypersensitivity
Local type II hypersensitivity