Modified Protection against Toxoplasma gondii Lethal Infection and Brain Cyst Formation by Vaccination with SAG2 and SRS1.

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Abstract
Numerous studies have supported the importance of immunity to SAG1, the most predominant antigen of Toxoplasma tachyzoite, in protection against Toxoplasma gondii infection. Nevertheless, vaccination with SAGI provides insufficient protection when compared with that of Toxoplasma lysate (TL). In order to screen the Toxoplasma antigens for immunogenic potential shown by modified protection or induction of specific immune response after infection, recombinant antigens were prepared in Eschericha coli using DNA fragments corresponding to SAG1, SAG2, SAG3, SRS1 and P54 of T. gondii RH strain maintained in our laboratory. Each of the recombinant antigen products or a mixture of the five antigens (Mix) was used to vaccinate mice. Mice then received a lethal dose of T. gondii. Up to 25% of the mice vaccinated with SAG2, SRS1, P54 and Mix survived, whereas there were no survivors in gene 10- (negative control), SAG1- and SAG3- vaccinated groups. In all the survivors, brain cysts were not observed. Conversely, vaccination with TL almost completely protected mice in the acute phase but permitted brain cyst formation and resulted in gradual decrease of survivors to 33% during 4 months of experiments. Western blot analysis on convalescent sera showed an extensive IgG induction to a 30 kDa antigen in TL-vaccinated mice, a 22 kDa in SAG2-vaccinated mice and a 55 kDa in P54-vaccinated mice. The protection modified by boost in specific antibody is suggestive of the immunogenic potential of SAG2, SRS1 and possibly P54 against T. gondii infection.