A Purified Saponin Acts as an Adjuvant for a T-Independent Antigen

Abstract

Three strains of mice were injected with a T-independent antigen, Escherichia coli 055:B5 polysaccharide (PS) combined with purified saponin, QS-21, isolated from Quillaia saponaria bark. PS was prepared by hydrolysis of lipopolysaccharide (LPS). Nine week old mice were injected intradermally with 60 ug PS, as determined by an anthrone assay, with or without 15 ug QS-21 on days 0 and 14. On day 22 sera were assayed by EIA for PS specific antibodies. Titers were 11-fold higher in CD-1 mice with QS-21. C3H/HeJ (lps^d) and C3H/HeSnJ (lps^r) mice also showed an adjuvant associated increase in titer with saponin. Therefore, LPS responsiveness was not required for the adjuvant effect. PS vaccinated C3H and CD-1 mice with and without QS-21 had similar antibody isotype profiles. lgG2b titers accounted for more than half of the total Ig response. lgG2a was next highest followed by lgG3, IgM, lgG1, and IgA. In comparison, CD-1 mice injected with 0.1 ug intact LPS had a different LPS specific isotype profile. lgG3 was the highest followed by lgG1, lgG2b, IgM, lgG2a, and IgA.