LEARNING OBJECTIVES: Type I hypersensitivity reactions uniquely involve the IgE class of
immunoglobulins (Ig). IgE differs from other classes of Ig in that the majority of the antibodies
are bound to high affinity IgE FcɛRs that are expressed on a variety of cell types. Some of
these cell types, most notably, mast cells and basophils, are triggered to undergo rapid
activation, degranulation, and release of bioactive mediators following binding of antigen to
FcɛRI-bound IgE. Because of the central role that IgE antibodies and these mediators play …