Adjuvant effects of orally administered saponins on humoral and cellular immune responses in mice

We have described adjuvant effects of orally administered Quillaja saponins on the immune responses of mice fed inactivated rabies antigen (AG). The in vivo lymphocyte proliferation in mice fed antigen + saponin (AG + SAP) was significantly greater than that in mice fed antigen (AG) alone. Further, the mitogen-induced cell proliferative responses in animals primed with AG + SAP was markedly increased compared with those in the AG group. These changes in clonal expansion were associated with an enhanced helper T cell (Th) and B cell co-operation. The in vivo cell proliferation and in vitro mitogen-induced responses of mice fed AG + SAP correlated with enhanced antibody synthesis. In mice fed saponin alone, there were significant increases in clonal expansion and lymphocyte function. Our present data indicate that the immunocompetence in animals fed AG + SAP was indeed evoked by saponins. Cytotoxic T lymphocyte activity in mice fed SAP or AG + SAP was detected 7 days after booster, in contrast to 21 days in mice fed AG alone. The natural killer cell activity in mice fed SAP alone was greatly enhanced and persisted for an extended period of time.