Submitted to: Molecular and Biochemical Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 15, 1998
Publication Date: N/A
Interpretive Summary: Neosporosis is a parasitic disease that appears to be a major cause of abortion in dairy cattle in the U.S.A. and worldwide. Congenital transmission of the causative organism, Neospora caninum, to the fetus may result in abortion, stillbirth, delivery of a diseased calf which dies a few days after birth, or birth of an apparently normal, but infected calf which can transmit the parasite to it s own offspring. The present study was conducted to study the subcellular location of an N. caninum protein (called NCDG2) that can be used for the diagnosis of neosporosis in a variety of animals including cows. Using genetic engineering techniques our laboratory has isolated and partially characterized the entire DNA sequence encoding this protein. The gene sequence was introduced into the bacterium Eschericia coli to allow production of the recombinant antigen that is similar to the protein derived from the parasite. Recombinant NCDG2 is recognized by sera from N. caninum-infected cows. In electron microscopy studies, the protein was located within the dense granules found inside the parasite and, to a limited extent, was also found on the external surface of the parasite. These experiments, and work from others, such as Toxoplasma gondii, indicate that NCDG2 may be useful as a vaccine antigen against neosporosis.
Technical Abstract: A full-length cDNA encoding a dense granule protein (designated NCDG2) from the protozoan parasite Neospora caninum was cloned and expressed as a ~33 kDa polyhistidine fusion protein in Eschericia coli. Northern blotting analysis revealed the NCDG2 gene was transcribed as a 1.6 kb mRNA in tachyzoites. Antisera raised against E. coli-derived recombinant NCDG2 bound a ~37 kDa N. caninum tachyzoite protein in Western blotting. Immunoelectron microscopy showed this antigen to be associated with the dense granules of N. caninum tachyzoites and potentially secreted in the host cell. The recombinant protein NCDG2 was recognized by sera from cows with confirmed neosporosis-associated abortion. Homology searches of nucleotide and protein sequence databases showed that the NCDG2 predicted protein sequence was similar to GRA-6, a T. gondii protein also associated with the dense granules in this organism.