Adjuvant activity of saponin: antigen localization studies.

The adjuvant saponin potentiates the antibody response of mice to the antigen keyhole limpet hemocyanin (KLH). Studies using 125I-labelled KLH show that saponin significantly prolongs the retention of antigen at the subcutaneous injection site and also increases the amount reaching the spleen. Both these phenomena were associated with the inflammatory response to saponin and were markedly reduced following abolition of the inflammatory action of saponin by addition of cholesterol-containing liposomes. The adjuvant action of saponin was not modified by this treatment. Further evidence that neither antigen retention nor splenic localization is implicated in the adjuvant action of saponin for KLH is the demonstration that digitonin, which shares hemolytic and cholesterol binding activity with saponin, caused similar antigen retention and splenic localization but was not adjuvant active.