Adjuvant and suppressive effects of Grass Conjuvac and other alginate conjugates on IgG and IgE antibody responses in mice.
BALB/c mice were immunized with grass pollen extract (GPE), GPE conjugated to sodium alginate (Conjuvac) or GPE absorbed to aluminium hydroxide gel (alum). Conjuvac was a more potent immunogen than the other two preparations of GPE when anti-GPE IgG antibody levels were compared. In contrast, the highest IgE antibody titres in the Conjuvac treated mice, were some sixteen-fold lower than the highest titres in the mice immunized with GPE in alum. The suppressive effects of Conjuvac on IgE antibody titres were also studied. Mice were immunized with 1 microgram dinitrophenyl (DNP)-GPE in alum and the anti-DNP and anti-GPE IgE antibody titres determined. After 4 and 5 weeks, the mice were injected with GPE or Conjuvac. The Conjuvac and the GPE failed to reduce the ongoing primary anti-GPE IgE responses but both suppressed the secondary responses by up to eight-fold. The suppression was not dose-related however. The ongoing primary and secondary anti-DNP IgE titres were suppressed in a dose-related manner by up to sixty-four fold by Conjuvac but GPE treatment was much less suppressive. We went on to investigate the suppressive properties of DNR-alginate (DNP-alg) conjugates. In these experiments mice were immunized with 1 microgram DNP-ovalbumin (DNP-OA) mixed with alum. After 4 and 5 weeks, the mice were injected with a dose of 6--600 micrograms DNP-alg with an average hapten density of 2 or 10 per alginate molecule. After a further 8 weeks a second injection of 1 microgram DNP-OA was given. All dose levels of both DNP-alg conjugates suppressed the continuing primary as well as the secondary anti-DNP IgE responses. It is concluded that alginate has properties similar to those of known T-cell adjuvants and that Conjuvac may prove useful in the immunotherapy of atopic allergy.