Studies on the cellular site of action of the adjuvant activity of saponin for sheep erythrocytes.

Saponin, which complexes with cholesterol in cell membranes, is a powerful adjuvant for antigens such as whole cell protozoal vaccines and SRBC. Saponin attached to SRBC ghosts potentiated the humoral response; but injection of saponin 1 or 2 days before or after SRBC at the same subcutaneous site was also effective. After the subcutaneous injection of saponin and SRBC the cellularity of the draining lymph node increases sixfold, and indirect PFC appear in it and the spleen. Splenectomy increases immunopotentiation by saponin, but T cell depletion abolishes it. The data show that attachment of the saponin to the antigen is not essential, and suggest that the adjuvant effect, which is T cell dependent, is exerted on host cells in the draining lymph node.