Hypersensitivity and types of hypersensitivity?

Hypersensitivity is when an otherwise healthy immune system has an undesirable
exaggerated response to a foreign substance (or perceived foreign substance) that damages the
body’s own cells.
Type I Hypersensitivity is triggered by an innocuous foreign substance (like dust, pollen
or animal dander) that would cause no problems in the majority of people. The antigen
simultaneously binds more than one membrane bound IgE on a mast cell (or basophil). This
process, called Crosslinking, triggers the release of mast cell granules full of histamine.
Histamine then goes on to signal the various changes associated with allergies similar to how it
functions during acute inflammation. This allergic reaction happens almost instantly and the
symptoms can become evident within minutes. This is possible because the mast cells are Pre-
Sensitized to the innocuous substance which means they have pre-formed membrane bound IgE
that recognizes the particular innocuous antigen.
To be...