Tight junctional inhibition of entry of Toxoplasma gondii into MDCK cells

Detection and characterization of excretory/secretory proteins from Toxoplasma gondii by monoclonal antibodies

Excretory/secretory proteins (ESP) from Toxoplasma gondii were analyzed to define the function in the penetration process into host cells. Whole ESP obtained at 37 degrees C were composed of 15 bands with molecular mass of 110, 97, 86, 80, 70, 60, 54, 42, 40, 36, 30, 28, 26, 22, and 19 kDa. Five ESP of 86, 80, 42, 36, and 28 kDa were reacted with monoclonal antibodies (mAb), named as Tg386 (microneme), Tg485 (surface membrane), Tg786 (rhoptry), Tg378, and Tg556 (both dense granules), respectively. The ESP was released by a temperature-dependent/-independent manner and all at once whenever ready to pour out except Tg786. Each ESP was not exhausted within the parasite but the amount was limited. Tg786 was released continuously with increment, whereas Tg378 and Tg556 were ceased to release after 3 and 4 hr. Dense granular Tg378 and Tg556 were released spontaneously and constitutively before the entry into host cells also. The entry of T. gondii was inhibited by all the mAbs differentially. And the parasite deprived of ESP was inhibited to enter exponentially up to 90.1%. It is suggested that ESP play an essential function to provide appropriate environment for the entry of the parasite into host cells.

Effects of gamma-irradiation on intracellular proliferation of Toxoplasma gondii RH tachyzoites

A quantitative assay was performed on the effects of gamma-irradiation (30-300 Gy) on intracellular proliferation of Toxoplasma gondii RH tachyzoites in human leukemic HL-60 cells and murine peritoneal macrophages by means of 3H-uracil uptake assay. Infected non-irradiation group (NI) and uninfected group (incubating only host cells) were prepared. The 3H-uracil uptake by tachyzoites of NI group 12-24 hrs after infection was 2,190-4,787 counts per minute for macrophages and 2,967-8,254 for HL-60 cells, whereas the irradiated tachyzoites revealed only 381-703 (100 Gy) and 218-408 (300 Gy) for macrophages, and 1,911-2,618 (30 Gy), 1,253-1,384 (70 Gy), 1,013-1,090 (100 Gy), and 483-588 (300 Gy) for HL-60 cells. The proliferation inhibition rate was similar in macrophages and HL-60 cells, for example, 89-94% and 80-94% respectively by 300 Gy, 12-24 hrs after infection. It is concluded that RH tachyzoites of T. gondii are severely affected by gamma-irradiation in their capability of intracellular proliferation.

Inhibition of entry of Toxoplasma gondii into MDCK cells by fetal bovine serum

We experienced the partial inhibition of entry of Toxoplasma gondii into MDCK cells when the FBS was depleted from media. MDCK cells and Toxoplasma (RH strain) were co-cultured, the penetration was inhibited up to 60-80% with concentration-dependence of FBS. Inhibitory effect was clear when the conc. of FBS was over 1% (v/v) with 50% inhibition conc. of 5%. When Toxoplasma was pre-incubated with FBS and then applied to MDCK cells, there were no inhibitory effect, but when FBS was added to Toxoplasma-MDCK co-culture, the time of adding was critical with rapid inhibition. And when FBS was further treated with heat (95 degrees C, 10 min), the inhibitory effect was decreased slightly in both raw and inactivated FBS. The FBS factor(s) might participate to neutralize secreted materials which enhancing penetration or intervene between receptor-ligand binding at the moment of entry through sterically rather than functionally.

[Comparative susceptibility of different cell lines for culture of Toxoplasma gondii in vitro]

In order to establish a useful cell culture system for T. gondii, we compared the degree of proliferation of T. gondii tachyzoites among 8 different cell lines; 2 kinds of normal animal cells (MDCK-canine kidney cells; Vero-monkey kidney cells) and 6 kinds of human tumor cells (A 549, PC 14-lung cancer cells; SNU 1, SNU 16, MKN 45-stomach cancer cells; HL-60-promyelocytic leukemia cells), through morphological observation and 3H-uracil uptake assay. The degree of susceptibility to infection with T. gondii tachyzoites was highest in A 549 and PC 14 cells, medium in Vero, HL-60, MDCK and SNU 1, and lowest in SNU 16 and MKN 45 cells. The kinetics of T. gondii multiplication during the post-infection 60 hours were highly dependent upon the dose of tachyzoites administered and the duration of cultivation. These results show that A 549 and PC 14 are the most suitable cell lines among the 8 tested for the growth and multiplication of T. gondii in vitro.

Cell cycle-dependent entry of Toxoplasma gondii into synchronized HL-60 cells

The degree of attraction of Toxoplasma gondii to vertebrate cells varies with cell type and cell phase. Human promyelocytic leukemia cells, HL-60, were synchronized by double thymidine block method and co-cultured with Toxoplasma for 1 hr at each cell stage to investigate the cell cycle specific susceptibility of parasites to host cells. For 30 hr the average number of Toxoplasma that invaded was a little changed except at 3 hr from G1/S phase boundary which concurred with the peak point of DNA synthesis. At 3 hr which is a relatively short interval compared to whole S phase, modification of cells by parasitic invasion was most remarkable. The number of Toxoplasma that penetrated was increased to more than six times. The shape of the cells became sludgy and almost indiscernible by strong accessibility of parasites only for an hour of mid-S phase. The same fluctuation was also observed at the second peak of S phase but weakly. This suggests that there be surface molecules concerning with the attachment of Toxoplasma to the host cells, which is expressed at special point of S phase. Further studies on the specific protein or similar molecules related could be carried out using synchronized HL-60 cells.