Toxoplasma gondii RH Ankara: production of evolving tachyzoites using a novel cell culture method.

Toxoplasma gondii is one of the most researched parasite due to its easy growth both in vitro and in vivo. Tachyzoites, derived from mouse or rat peritoneum encounters ethical and economical problems when used for research or diagnostic purposes. Currently, research has focused on determining the most suitable cell culture environment to reach highest amount of viable tachyzoites with least host cell contamination. However, gene expression changes that take place throughout the adaptation of evolving T. gondii strains to continuous cell cultures appear as a problem. The present study aimed to determine a novel cell culture strategy for T. gondii RH Ankara strain tachyzoites to harvest abundant tachyzoites with least host cell contamination and minimal antigenic variation at predetermined dates to use as an antigen source in serological assays that will facilitate reduction in animal use. To achieve this purpose, T. gondii RH Ankara strain tachyzoites were incubated with HeLa cell at different ratios for two or three days. In all flasks incubated for two days, viability rate reached to 100% and HeLa cell contamination decreased to levels between 0.12-0.5×10(6)/ml. In the flasks with HeLa-tachyzoite ratio 1/8, the tachyzoite yield and viability ratio were 3×10(6)/ml and 100%, respectively, with accompanying 10 fold decrease (0.12×10(6)/ml) in HeLa contamination. During continuous production, highest tachyzoite yield was obtained from the first passage (3.55×10(6)/ml) and until the end of third subculture viability rates and HeLa cell contaminations were between 98.2-99.4% and 0.31-0.37×10(6)/ml, respectively. ELISA, IFA and Western blot analyses showed that the quality, specificity and sensitivity of the antigen harvested from the first passage of cell culture performed at two days intervals were comparable to the antigen harvested from mice and decreased in the following subcultures. Overall, these results demonstrated that T. gondii RH Ankara strain is still evolving to adapt to cell culture environment and therefore such strains continuously produced in cell cultures should be avoided for serological assays. However, the two day short interval cell culture method described herein offers a chance to reduce the animal use intended for the preparation of serological assays' antigen from local evolving strains.