Studies on the Tissue Culture of Toxoplasma gondii with HeLa Cells

Several observations were made on the tissue culture of Toxoplasma gondii (RH strain) with use of HeLa cells for a host cell line, with the object of obtaining the fundamental knowledge of the growth of the parasite in the tissue culture. To assess the growth of the parasite in the tissue culture, the infection rate of HeLa cells and the relative number of infective parasites were counted: the former was expressed by the percentage value of the number of HeLa cells invaded by the parasite, among the total HeLa cells observed, and the latter by the total number of parasites found in 100 HeLa cells on a microscope. Results achieved were summarized as below: 1) The infection rate of HeLa cells ascended up to 6 hours after the parasite inoculation into the HeLa cell culture, then trended to a gradual descent. The relative number of infective parasites was found to keep a rise up to 9 hours after the parasite inoculation into the culture. 2) The addition of lysozyme (1 mg/ml or more) or hyaluronidase (6 units/ml or more) into the tissue culture of the parasite brought about an increase of the infection rate of HeLa cells as well as the relative number of infective parasites. 3) The pretreatment of the parasite with sulfisoxazole (10 mg/ml) for 4 hours or sulfathiazole (10 mg/ml) for 2 hours shortly before the parasite inoculation into the HeLa cell culture did not appear to inhibit the growth of the parasite in a 6-hour cultivation. 4) The pretreatment of the parasite with 1% of the HA (Hemagglutination test)-positive human serum (HA-titre 4,096×) or 0.01% of the rabbit immune serum (HA-titre 65,536×) for 30 minutes or longer resulted in a noticeable reduction of the relative number of infective parasites in a 6-hour cultivation