Immunoglobulin E (IgE) is a kind of antibody that has only been found in mammals. IgE’s main function is immunity to parasites such as helminths like Schistosoma mansoni, Trichinella spiralis, and Fasciola hepatica. IgE is utilized during immune defense against certain protozoan parasites such as Plasmodium falciparum. IgE also has an essential role in type I hypersensitivity, which manifests various allergic diseases, such as allergic asthma, most types of sinusitis, allergic rhinitis, food allergies, and specific types of chronic urticaria and atopic dermatitis. IgE also plays a pivotal role in responses to allergens, such as: anaphylactic drugs, bee stings, and antigen preparations used in desensitization immunotherapy. Although IgE is typically the least abundant isotype — blood serum IgE levels in a normal individual are only 0.05% of the Ig concentration — it is capable of triggering the most powerful inflammatory reactions.
Atopic individuals can have up to 10 times the normal level of IgE in their blood. IgE is known to be elevated in various autoimmune disorders such as Lupus (SLE), Rheumatoid Arthritis (RA) and psoriasis, and is theorized to be of pathogenetic importance in RA and SLE by eliciting a hypersensitivity reaction.