Abstract
Abstract Rat IgE identified by its physicochemical and antigenic characteristics was shown to mediate the immunologic release of both histamine and slow-reacting substance of anaphylaxis (SRS-A) in the rat. The antibodies in homocytotropic antiserum which mediated histamine and SRS-A release after a 2-hr latent period were shown to be heat-labile, to elute on DE-52 cellulose chromatography and Sephadex G-200 gel filtration in the fractions known to contain rat IgE, and to sediment as an approximately 8S immunoglobulin on sucrose density gradient ultracentrifugation. Absorption with mono-specific guinea pig anti-IgE strikingly reduced the capacity of homocytotropic antiserum to mediate passive cutaneous anaphylaxis or the intraperitoneal release of histamine and SRS-A, thereby establishing that these biologic activities of homocytotropic antiserum are attributable to an antigenically unique rat immunoglobulin. The release of histamine and SRS-A mediated by rat IgE is dependent on the participation of the mast cell but does not require the circulating polymorphonuclear (PMN) leukocyte or an intact complement system, thus differing from the PMN leukocyte- and complement-dependent pathway to SRS-A release mediated by the IgGa antibodies of hyperimmune serum.
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