The coccidian parasite Neospora caninum is an intracellular protozoan, causing abortion in cattle in many countries around the world. In this study, the protective potential of the major N. caninum
surface antigen NcSRS2, expressed in Escherichia coli and formulated into
immunostimulating complexes (
iscoms), was investigated in an experimental mouse model. The
recombinant protein was specially designed for binding to
iscoms via
biotin-
streptavidin interaction. Two groups of 10 BALB/c mice were immunised twice, on days 0 and 28 with
iscoms containing either the recombinant NcSRS2 (NcSRS2
iscoms) or similar
iscoms with NcSRS2 substituted by an unrelated recombinant
malaria peptide (M5) as a control (M5
iscoms). A third group of 10 age-matched BALB/c mice served as an uninfected control group. Immunisation with recombinant NcSRS2
iscoms resulted in production of substantial antibody titres against N. caninum
antigen, while the mice immunised with M5
iscoms produced only very low levels of
antibodies reacting with N. caninum
antigen. After challenge
infection with N. caninum tachyzoites on day 69, mice immunised with NcSRS2
iscoms showed only mild and transient symptoms, whereas the group immunised with M5
iscoms showed clinical symptoms until the end of the experiment at 31 days post inoculation. A competitive PCR assay detecting Nc5-repeats was applied to evaluate the level of parasite
DNA in the brain. The amount of Nc5-repeats in the group vaccinated with NcSRS2
iscoms was significantly lower than in the control group given M5
iscoms. In conclusion, it was found that the recombinant NcSRS2
iscoms induced specific
antibodies to native NcSRS2 and immunity sufficient to reduce the proliferation of N. caninum in the brains of immunised mice.