Type I (atopic or anaphylactic) Hypersensitivity
Type I following the Gell and Coombs Classification . Allergic reactions are classified
depending on the type of tissue damage that develops. A Type I reaction occurs when an
antigen entering the body encounters
mast cells or basophils . These types of immune
defense cells have antibodies attached to their surfaces and the antigen
binds to this. The result is the release of histamine , causing blood vessel
dilation and a narrowing of the airways .