Immune responses to foot-and-mouth disease DNA vaccines can be enhanced by coinjection with the Isatis indigotica extract.

The Isatis indigotica extract is widely used in clinical practice for the treatment of influenza, epidemic hepatitis, epidemic encephalitis B etc. The goal of this study was to investigate whether coinjection of the Isatis indigotica extract with foot-and-mouth disease virus (FMDV) DNA vaccine could increase the protective immune response. Mice were vaccinated twice with either FMDV DNA vaccine plus the Isatis indigotica extract or DNA vaccine alone. Compared with the group of DNA vaccine alone, in the group that received DNA vaccine plus the Isatis indigotica extract was observed a significant increase in not only FMDV-specific antibody response but also T cell proliferation assay. All swine immunized with either FMDV DNA vaccine plus the Isatis indigotica extract or DNA vaccine alone were partially protected from FMDV challenge, but the signs of DNA vaccine plus the Isatis indigotica extract group were less severe than that of DNA vaccine alone. Coinjection of the Isatis indigotica extract with DNA vaccine has adjuvant effect on the immune response against viral pathogens and its application provides an effective strategy to improve the efficacy of DNA vaccines.