Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/20/2005
Publication Date: 10/20/2005
Citation: Tuo, W., Fetterer, R.H., Jenkins, M.C., Dubey, J.P. 2005. Neospora caninum immunophilin stimulates interferon-gamma production. Meeting Abstract.
Technical Abstract: Interferon-gamma (IFN-gamma) response is necessary for the development of a host protective immunity during infection by intracellular parasites. Neosporosis which is caused by the intracellular protozoan parasite Neospora caninum is known to be fatal in IFN-gamma deficient hosts. However, the mechanism to elicit IFN-gamma by the invading parasite is unclear. This study has identified a microbial protein in the N. caninum tachyzoite, the N. caninum immunophilin, as a major component of the parasite responsible for inducing IFN-gamma production by bovine peripheral blood mononuclear cells (PBMC) and antigen-specific CD4+ T cells. The immunophilin has high sequence homology (86%) with the T. gondii 18 kDa cyclophilin, and has a calculated molecular mass (Mr.) of 19.4 kDa. The immunophilin is a secretory protein with a predicted signal peptide of 17 amino acids. The immunophilin has detectable peptidylprolyl isomerase activity and may not be N-glycosylated although potential glycosylation sites are present. The immunophilin was detected in whole-cell N. caninum tachyzoite lysate (NcAg) and in culture supernatant of live N. caninum tachyzoite. In N. caninum tachyzoite culture supernatant, three immmunophilin bands of 19, 22, and 24 kDa were identified, whereas only two bands of 19 and 24 kDa were detected in whole-cell tachyzoite lysate. NcAg induced high level os IFN-gamma aproduction by PBMC and CD4+ T cells in vitro. IFN-gamma-inducing effect of NcAg was blocked by cyclosporin A (CsA), a specific ligand for immunophilin, in a dose-dependent fashion. Furthermore, CsA abolished immunophilin-induced IFN-gamma aproduction by PBMC from naive cows and PBMC and CD4+ cells from immune cows, suggesting that IFN-gamma induced by immunophilin may not rely on antigen stimulation. These results indicate that the N. caninum tachyzoite naturally produces an IFN-gamma-inducing protein, immunophilin, which may in part mediate parasite survival as well as host protection.