Evaluation of the adjuvant properties ofAstragalus membranaceusandScutellaria baicalensisGEORGI in the immune protection induced by UV-attenuatedToxoplasma gondiiin mouse models

Human vaccines are not available and current anti-toxoplasma treatment is disappointing. To investigate the possible adjuvant effect of aqueous extracts obtained from medicinal herbs ofAstragalus membranaceus(Am) andScutellaria baicalensisGEORGI (Sb) on the immune response toToxoplasma gondiiin the mouse models induced by ultraviolet (UV)-attenuatedT. gondii, this paper studies the possible vaccination strategies to help combat infections withToxoplasmaand looking towards developing new vaccine and approaches. We used UV-attenuatedT. gondii(UV-T.g) of RH strain as a vaccine and the extracts ofAm(AmE) andSb(SbE) as adjuvant. Mice were infected by intraperitoneal (i.p.) injection of 102RH tachyzoites alone (infected controls), infected and treated withAmE (T.g+AmE) andSbE (T.g+SbE), respectively; and mice immunized i.p. with UV-T.galone, UV-T.gco-administrated withAmE (UV-T.g+AmE) orSbE (UV-T.g+SbE), and then challenged withT.g, respectively. The animal survival time, parasite burden in peritoneal lavage fluids, liver histopathological analysis, and levels of serum antibodies among the groups were compared after either infection or challenge. The results showed that, compared to infected controls, infected mice treated withAmE orSbE, or vaccinated mice and then challenged, had significantly prolonged survival time, decreased parasite burden, improved liver histopathological score, and increased Th1-type cellular immune response; furthermore, vaccinated mice co-administrated withAmE orSbE had even longer survival, lower parasite burden, lower liver histopathological score, and higher Th1 response after challenge. Our data demonstrated that the protective immunity of UV-attenuatedT. gondiicould be markedly enhanced byAmE orSbE co-administration, which suggests that bothAmE andSbE may have the potential to be used as effective vaccine adjuvant.