Alum augments the experimental allergenicity of Kunitz-type soybean trypsin inhibitor independent of the antigen-adsorption

In order to inspect the significance of the adsorbing property in the adjuvant activity to enhance IgE production, we immunized BALB/c mice against Kunitz-type soybean trypsin inhibitor (KSTI), the most potent experimental allergen among soybean proteins, associated with Aluminum hydroxide (alum) or DEAE-Sephadex particles. The production of immunoglobulin isotypes was analyzed at the various amounts, 3-3,000 microg per mouse, of the antigen dosages. In our experiments, although alum did not adsorb KSTI significantly, it augmented the total and the antigen-specific IgE without affecting the optimal range of the antigen dosage. On the other hand, alum did not effectively enhance the production of the other immunoglobulin isotypes. The production of immunoglobulin isotypes other than IgE increased dose-dependently on the antigen. These results ensured our previous finding that another protein, ovalbumin, was used as the antigen. We also demonstrated that the adsorption of KSTI by DEAE-Sephadex in the immunizing vehicle resulted in the requirement of more KSTI for accomplishing the equal immunity in BALB/c mice compared to the control. Moreover, we demonstrated that, regardless of the inability to adsorb KSTI, alum exerted its adjuvant activity only when it was co-injected with the antigen. These results showed that some biochemical effect, other than adsorptive activity, to enhance the production of the antigen-specific IgE resides in alum.