Mice given a single subcutaneous inoculation of highly-purified ovalbumin in water-in-oil emulsion yielded peak antibody titres which were about 500 times those stimulated by the same dose of ovalbumin without adjuvant, and which remained at the peak level for at least a year. Neither the oil, nor the emulsifier, nor the emulsion itself when injected at a separate site from the antigen, stimulated a response of this type. The response was not affected by a simultaneous subcutaneous injection of anti-ovalbumin, or by the later inoculation of a different antigen in water-in-oil emulsion, or by further inoculations of ovalbumin in saline.
Ovalbumin was detectable in emulsion recovered from injected mice for up to 544 days after inoculation and its half-life within the emulsion was found to be about 90 days.
The observations indicated that this type of adjuvant may exert its effect solely by the slow and even release of very tiny quantities of antigen over a long period of time. A mechanism by which such a release may take place is suggested.