Plasmodium berghei: The effects of suppressor factor on vaccination

Suppressor factor-free known protective fractions (G, Sp2) extracted from Plasmodium berghei-infected erythrocytes were injected into groups of mice with and without suppressor factor (SF). One, two and three injections of SF did not significantly alter the mortality rate or the mean day of death of vaccinated animals. Peaks obtained during the preparation of SF, which were free of SF, were tested for protection. Peak three of this preparation, which is enhancing in the plaque cell test, gave no protection after three vaccinating injections, but 10 daily injections during infection did give significant protection. Three vaccinating injections of SF did not induce sufficient SF inhibitory response to alter the mean day of death or the mortality rate. The presence of SF in vaccine material probably does not greatly affect its protective activity since 10 injections of SF following infection were required to alter the response.