One of five classes of immunoglobulins made by humans (the others being IgA , IgD , IgG and IgM ). Main function seems to be to protect the host against invading parasites. While parasitic disease may not be a major clinical issue in most industrialized nations, it is a major public health problem in developing nations. The antigen-specific IgE interacts with mast cells and eosinophils to protect the host against the invading parasite. However, the same antibody-cell combination is also responsible for typical allergy or immediate hypersensitivity reactions such as hay fever , asthma , hives and anaphylaxis .

There are two major types of receptor for the Fc portion (back) of the IgE or IgG4 molecule on cells . One, a high affinity receptor, is found primarily on mast cells and basophils . The other is a low affinity receptor found on CD23 cells. IgE attaches to these and acts as an antigen receptor.

This class of immunoglobulins is distributed throughout the body, although cells synthesizing IgE are found predominantly in association with mucosal tissues. IgE-bearing cells are also found in large numbers in the neonatal GALT , which on maturation revert to IgA and IgM synthesis. Little is known of the traffic of IgE-bearing or IgE-producing cells. If there is traffic of IgE cells it is less extensive than the IgG system - IgE is not found in breast milk, and only in very low amounts in other secretions such as saliva.

Reagin is the allergist's term for IgE antibodies.