Modulation of the IgE antibody response in rats to Kentucky blue grass pollen allergens.

The low molecular weight dialyzable fraction (D) prepared from the aqueous extract of Kentucky Blue Grass pollen was shown to suppress the formation of IgE antibodies in rats immunized with the nondialyzable fraction (R). In an attempt to establish the nature of the constituents responsible for this suppression, D was fractionated by gel filtration through Sephadex G-25. The first fraction eluted (DI) elicited skin reactions in rats sensitized with a rat reaginic serum to R and also gave a precipitate with a rabbit antiserum to R. A later fraction (DIII) was devoid of these two properties. To investigate the effects of these fractions on the antibody response, rats received either DI or DIII, administered in saline, prior to their immunization with R in presence of aluminum hydroxide. Pretreatment with DI resulted in a reduction of IgE antibody levels as compared with the IgE antibody response in control animals which had received pretreatment only with saline; however, pretreatment with DI did not affect the anti-R-hemagglutinating titers. In contrast, pretreatment with DIII enhanced both the IgE and the hemagglutinating antibodies. Hence, it is concluded that the composite fraction D contains one group of constituents capable of suppressing and another of enhancing the IgE antibody response.