IDENTIFICATION AND PARTIAL CHARACTERIZATION OF A 36 KDA SURFACE PROTEIN ON NEOSPORA-CANINUM TACHYZOITES

Neospora caninum, the causative agent of neosporosis, is a recently id entified 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 involv ed 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 a nd mere 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 pres ent in 2 isolates of Neospora (NC-1 and Liverpool), but was absent in Toxoplasma (RH-strain) tachyzoites. Immunofluorescence and pre-embeddi ng immunogold transmission electron microscopy employing affinity-puri fied anti-Nc-p36 antibodies showed that the Nc-p36 is a cell surface-a ssociated protein. Immunogold on-section labelling of LR-White-embedde d parasites, fixed prior and at defined time-points after host cell en try, demonstrated the presence of this molecule on the surface as well as within the dense granules of N. caninum tachyzoites.