A comparison of saponin with other adjuvants for the potentiation of protective immunity by a killedPlasmodium yoeliivaccine in the mouse

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Abstract
The protective immunity conferred by subcutaneous injection of outbred CD‐1 mice with a killedPlasmodium yoelii(YM strain) vaccine was strongly potentiated by saponin. By adjusting the dose of antigen, the number of immunizations and the number of living parasites in the challenge infection, conditions were defined where antigen alone was non‐protective but 100% protection was obtained by the addition of saponin. Inbred BALB/c, CBA/CA and C57 Bl mice were much less responsive than the CD‐1 mice. The following adjuvants were compared with saponin: mineral oil emulsions (Freund's incomplete and complete adjuvants); Al(OH)3(Alhydrogel); bacteria and synthetic bacterial derivatives (Bordetella pertussis, Corynebacterium parvumand muramyl dipeptide); surface active materials (digitonin, vitamin A, Arquad 18, dimethyldioctadecyl ammonium bromide, and the polyene antibiotics, Nystatin and Amphotericin B). None of these adjuvants were as effective as saponin, although FCA, Al(OH)3and C.parvumaugmented immunity considerably. The possible reasons for the efficacy of saponin as an adjuvant for protozoal vaccines are discussed. TheP. yoelli/mouse system provides a sensitive and rapid screening assay for comparison of potential adjuvants suitable for use with a malaria vaccine.