Dai W, Pan H, Kwok O, Dubey J P
Molecular Biology Laboratory, Hipple Cancer Research Center, Dayton, OH 45439.
J Interferon Res. 1994 Dec;14(6):313-7. doi: 10.1089/jir.1994.14.313.
Interferon-gamma (IFN-gamma) is known to inhibit the growth of Toxoplasma gondii both in vivo and in vitro. The IFN-gamma induced anti-toxoplasma activity in human cells is strongly correlated with the degradation of the essential amino acid L-tryptophan in vitro. Destruction of L-tryptophan is due to an increased activity of indoleamine 2,3-dioxygenase (IDO), which is transcriptionally activated by IFN-gamma. To determine if indoleamine 2,3-dioxygenase alone is sufficient to block the T. gondii growth, we transfected human fibroblast cells with an IDO cDNA expression plasmid using a metallothionein-inducible promoter. We showed that IDO mRNA and its enzymatic activity are inducible in fibroblast cells transfected with right-orientation IDO cDNA upon addition of CdCl2 to culture medium. The elevated IDO enzyme activity is strongly correlated with an inhibition of T. gondii growth. No IDO mRNA nor enzyme activity is induced by CdCl2 in reverse orientation transfected cells, and no adverse effects were observed on T. gondii growth in cells transfected with the reverse IDO-construct or in control parent cells with or without supplementation of CdCl2. Our observations along with the recent report by Habara-Ohkubo et al. (Infect. Immun. 61, 1810-1813, 1993) suggest that IFN-gamma-induced antitoxoplasma activity is due at least in part to the activation of IDO gene.
已知γ-干扰素（IFN-γ）在体内和体外均能抑制刚地弓形虫的生长。在体外，IFN-γ诱导的人体细胞抗弓形虫活性与必需氨基酸L-色氨酸的降解密切相关。L-色氨酸的破坏是由于吲哚胺2,3-双加氧酶（IDO）活性增加所致，而该酶是由IFN-γ转录激活的。为了确定单独的吲哚胺2,3-双加氧酶是否足以阻断弓形虫的生长，我们使用金属硫蛋白诱导型启动子，将IDO cDNA表达质粒转染到人成纤维细胞中。我们发现，向培养基中添加CdCl2后，转染了正向IDO cDNA的成纤维细胞中IDO mRNA及其酶活性是可诱导的。IDO酶活性的升高与弓形虫生长的抑制密切相关。在反向转染的细胞中，CdCl2不会诱导IDO mRNA或酶活性，并且在用反向IDO构建体转染的细胞或添加或未添加CdCl2的对照亲本细胞中，未观察到对弓形虫生长的不利影响。我们的观察结果以及Habara-Ohkubo等人最近的报告（《感染与免疫》61, 1810 - 1813, 1993）表明，IFN-γ诱导的抗弓形虫活性至少部分归因于IDO基因的激活。
