Suppression of IgE responses by hyperimmune serum in rats

Recent work has shown that a relatively long-lasting suppression of egg albumin (EA)-specific IgE responsiveness occurs in the progeny of EA-immunized mother rats. This phenomenon can be duplicated by a course of EA-immune serum injections given to the neonatal progeny of normal mothers, and antigen-specific IgG was found to be the effective mediator. In order to elucidate further the mechanism of this selective suppression, the capacity of immune serum to suppress IgE responsiveness in adults was investigated. Pretreatment of adults with hyperimmune serum 3 weeks in advance of immunization was as effective as when the animals were neonatally treated. The possibility that the mediator responsible is the very small amount of EA-specific IgG remaining at the time of immunization was tested by injecting a small volume of immune serum simultaneously with immunization. This treatment also suppressed IgE responsiveness. The possibility that low levels of EA-specific antibody form complexes with the immunizing antigen is discussed.