Structural and molecular differences in the host parasite relationship between the enteric (coccidian) and exoenteric forms of toxoplasma gondii

The host parasite relationship of the enteric (coccidian) and exoenteric (tachyzoite, bradyzoite) forms of Toxoplasma gondii was examined in vivo by electron microscopy and immunocytochemistry. Significant structural and molecular differences were observed between the enteric and exoenteric forms. The expression and distribution of certain rhoptry and all the dense granule proteins was examined by immunocytochemistry. It is was observed that, while the antibody recognising ROP2,3,4 positively stain the anterior of the infective stages (merozoite, tachyzoite and bradyzoite) of both the enteric and exoenteric stages, ROP1 appeared to be absent from the merozoite. It was found that GRA8, like GRAsl-6, was present in both the tachyzoite and bradyzoite stages but did not appear to be expressed by the enteric stages. The only dense granule proteins expressed by the enteric (coccidian) stages were GRA7 and NTPase. By electron microscopy, the parasitophorous vacuole (PV) containing the enteric forms in the enterocytes of the cat was limited by a laminated wall consisting of three fused unit membranes. This is in contrast to the exoenteric stages where the PVs are limited by a single unit membrane. These differences point to a unique host/parasite relationship for the enteric stages of T. gondii. Copyright® 1999, The Research Center for Protozoan Molecular Immunology.