Intra-cisternal vaccination induces high-level protection against Neospora caninum infection in mice

Abstract

The efficacy of intra-cisternal (IC) immunization in preventing the dissemination of Neospora caninum tachyzoites into the brain was investigated. Mice were vaccinated intracisternally with tachyzoite extract in artificial cerebrospinal fluid (ACSF). For comparison, other groups were vaccinated via the intraperitoneal (IP) route with crude tachyzoite antigen extract, suspended either in Freund's incomplete adjuvant (FIA) or saponin. Subsequently, the mice were experimentally infected by IP administration of 2×10(6) N. caninum tachyzoites, and were monitored for 30 days. In the IP vaccinated mice, 22 and 33% of the mice from the adjuvant control groups (FIA and saponin, respectively) survived the challenge, and 66% of mice receiving Neospora tachyzoite extract in FIA and 55% of mice immunized with Neospora tachyzoite antigens in saponin. In the IC vaccinated group, all mice (8 out of 8) immunized with Neospora antigen remained clinically healthy, while only 2 out of 8 survived in the group treated with ACSF alone. Analysis of brain tissue showed a significantly reduced cerebral parasite load in IC vaccinated mice. Quantification of NcGRA2 transcripts in the IC vaccinated groups revealed that the viability of tachyzoites was severely impaired. Analysis of the humoral immune responses employing ELISA showed that the increased protection by IC vaccination was associated with a high IgG2a/IgG1 ratio, and analysis of cytokine transcript levels in spleen tissues at the end of the experiment, revealed a significant increase in mRNA coding for interferon-γ.