Reduced infection and protection from clinical signs of cerebral neosporosis in C57BL/6 mice vaccinated with recombinant microneme antigen NcMIC1

NcMICl is a 460 amino acid Neospora caninum microneme protein implicated in host cell adhesion and invasion processes. In this study, we assessed the potential protectivity of NcMICl-based vaccination against experimental N. caninum infection in mice, employing both recombinant antigen vaccines and DNA vaccines. Recombinant NcMICl (recNcMICl) was expressed in Escherichia coli as gluthatione-S-transferase-fusion protein. The corresponding NcMICl cDNA was cloned into the peDNA3.1 expression plasmid (peDNA-MICl), and expression was checked in transfected Vero cells. Mice (10 animals/group) were vaccinated either with recNcMICl antigen suspended in Ribi-adjuvant Q intraperitoneal injections), pcDNA-NcMICl (3 intramuscular injections), or pcDNA-NcMICl (twice intramuscularly), followed by I intraperitoneal recNcMICl antigen boost. Control groups included corresponding treatments with adjuvant, pcDNA3.1 without insert, and PBS (= infection control). All vaccinated and control groups were then challenged intraperitoneally with 2 X 10(6) N. caninum tachyzoites. Animals were inspected daily for a period of 3 wk postinfection (PI). At day 21, all animals were killed and assessed for infection. Before day 21 PI, clinical signs such as walking disorders, rounded back, apathy, and paralysis Occurred in infection Controls (50% of the mice), pcDNA and adjuvant controls (20% each), and the combined pcDNA-NcMICl/recNcMICl-treated group (30%). No clinical symptoms were observed in the recNcMICl and pcDNA-NcMICl vaccinated groups. All mice were positive for cerebral N. caninum infection as assessed by PCR of brain tissue. However, quantitative real-time PCR revealed that the infection intensity was significantly reduced in the group vaccinated with recNcMICl antigen. Immunohistochemistry confirmed these findings. In contrast, the infection intensity was highest in the group vaccinated with the pcDNA-NcMICl/recNcMICl combination, indicating that the sequential application of the DNA vaccine and recombinant antigen had a deleterious effect. Serological analysis showed that only recNcMICl-immunized animals generated detectable antibody levels recognizing native NcMICl Thus, of all protocols applied here, only recNcMICl vaccination appears to be suited to reduce cerebral infection in mice challenged with N. caninum tachyzoites.