Production and properties of Toxoplasma growth inhibitory factor (Toxo-GIF) and interferon (IFN) in the lymphokines and the circulation of Toxoplasma immune mice.

Assessment in vitro were carried out to study Toxo-GIF and IFN in lymphokines, LKs, produced by immune spleen cells with Toxoplasma lysate antigen (TLA). LKs were obtained from the cells after incubation for 24 to 48 h with TLA. They inhibited almost completely the intracellular multiplication of Toxoplasma (Tp) within homologous cells. Peak IFN activities were observed in the same LKs. The IFN was inactivated at pH 2, but did not lose its activity at 56 degrees C, suggesting that it might be type II or gamma IFN. Further evidence was presented of the coordinate production and properties of Toxo-GIF and IFN in the circulating blood of Tp-immune mice injected intraperitoneally with TLA or Poly I: C. The IFN was designated type II or gamma IFN. Its maximum activity appeared in Tp-immune mice 6 h after TLA or Poly I: C injection, while a maximum Toxo-GIF activity was observed in these mice 24 to 48 h after injection. Type I IFN activity was detected in the serum of normal mice injected with TLA or Poly I: C. Type I IFN differed markedly from type II IFN, because it was stable at pH 2 and unstable at 56 degrees C. Evidence was presented which emphasized the difference in activity in relation to the time of appearance between Toxo-GIF and IFN.