Immunology | Immune system| Immunity

           The potent biological activity of IgE allowed it to be identified in serum despite its extremely low average serum concentration.IgE antibodies mediate the immediate hypersensitivity reactions that are responsible for symptoms of hay fever,asthma,hives,and anaphylactic shock.The presence of a serum component responsible for allergic reactions was first demonstrated in 1921 by K.Prausnitz and H.Kustner,who injected serum from an allergic person intra-dermally into a nonallergic individual.When the appropriate antigen was later injected at the same site,a wheal and flare reaction(analogous to hives)developed there.This reaction,called the P-K reaction(named for its originators,prausnitz and kustner),was the basis for the fiorst biological assay for IgE activity.

a) Cross-linkage by a single allergen and b) Cross-linkage by a single IgG antibody to two allergen molecules.

          Actual identification of IgE was accomplished  by K.prausnitz and T.Ishizaka in 1966.They obtained serum from an allergic individual and immunized rabbits with it to prepare anti-isotype antiserum.The rabbits antiserum was then allowed to react with each class of human antibody known at that time(i.e.,IgG,IgA,IgM,IgD).In this way,each of known anti-isotype antibodies was precipitated and removed from the rabbit anti-serum.What remained was an anti-isotype antibody specific for an unidentified class of antibody.This antibody turned out to completely block the P-K reaction.the new antibody was called IgE(in reference to the E antigen of ragweed pollen,which is a potent inducer of this class of antibody).
         IgE binds to Fc receptors on the membranes of blood basophils and tissue mast cells.Cross-linkage of receptor-bound IgE molecules by antigen(allergen)induces basophils and mast cells to translocate their granules to the plasma membrane and release their contents to the extracellular environment, aprocess known as degranulation.As a result,a variety of pharmacologically active mediators are released and give rise to allergic manifestations.Localized mast-cell degranulation induced by IgE also may release for antiparasitic defense.