Systemic anaphylaxis is a shocklike and often fatal state that occurs within minutes of exposure
to an allergen. It is usually initiated by an allergen introduced directly into the bloodstream or
absorbed from the gut or skin. These symptoms are all due to rapid antibody-mediated
degranulation of mast cells and the systemic effects of their contents.
Localized Hypersensitivity Reactions:
In localized hypersensitivity reactions (atopy), the pathology is limited to a specific target tissue
or organ, and often occurs at the epithelial surfaces first exposed to allergens.
Hay fever: Symptoms result from the inhalation of common airborne allergens (pollens, dust,
viral antigens), which react with IgE molecules bound to sensitized mast cells in the conjunctivae
and nasal mucosa.
Allergic asthma: Degrnulation of