Thymidine uptake by chicken kidney cells parasitized by Eimeria tenella: evidence for a diffusable mediating substance.

The pattern of DNA synthesis in chicken kidney (CK) cells parasitized by Eimeria tenella was altered; a 2-fold increase in the uptake of [3-H]-thymidine occurred in these cells compared with that shown by the controls. This difference was significantly different at 16 h post-inoculation (p.i.) and reached a peak at 20 h p.i. Non-parasitized cells in co-culture with parasitized cells showed a level of incorporation intermediate between that of the parasitized and non-parasitized monocultures. It was shown that this stimulation was due to a factor released into the medium by the parasite or the parasitized cell. A possible course of events leading to induced and prolonged DNA synthesis by the host cell and the significance of this change in the life-cycle of the parasite is discussed.