Neospora caninum, the causative agent of neosporosis,
is a recently identified apicomplexan parasite which is structurally
and biologically closely related to, but antigenically distinct from,
Toxoplasma gondii. Molecules associated with the
surfaces of N. caninum tachyzoites are likely to participate in
the host cell entry process, could be involved in the interaction
of the parasite with the immune system, and they could influence the
pathogenesis of neosporosis. Isolated N. caninum
tachyzoites were extracted with the non-ionic detergent Triton X–114
and were further analysed using a polyclonal anti-N. caninum
antiserum. Immunoblots revealed several reactive bands, 1 of which
represented a glycoprotein of
approximately 36 kDa (Nc-p36). This molecule was present in 2 isolates
of
Neospora (NC-1 and Liverpool), but was
absent in Toxoplasma (RH-strain) tachyzoites. Immunofluorescence
and pre-embedding immunogold transmission electron microscopy
employing affinity-purified anti-Nc-p36 antibodies showed that the Nc-p36
is a cell surface-associated
protein. Immunogold on-section labelling of LR-White-embedded parasites,
fixed prior and at defined time-points after
host cell entry, demonstrated the presence of this molecule on the
surface as well as within the dense granules of N. caninum tachyzoites.