What are the properties of immunoglobulin E (IgE)?

Immunoglobulin E (IgE) is a monomer characterized by the presence of an epsilon heavy chain in its structure. It is primarily located extravascularly in the lining of the digestive and respiratory tracts and has a very short half-life of less than one day. This is because of the continuous removal and destruction of a part of the IgE molecule in endosomes. 

IgE is the largest Ig monomer due to the four CH domains. It has a molecular weight of 190,000 Da.

IgE is the least abundant antibody isotype present in plasma, with levels around 100 ng/mL, constituting just 0.002% of total immunoglobulins. Despite its low concentrations, IgE is highly biologically active and highly sensitive to allergens because it binds to high-affinity receptors on the surface of mast cells and basophils. FcεRI, a high-affinity receptor specific for IgE, is found at high densities on tissue-resident mast cells and basophils.