弓形虫ROP18结合宿主NMI抑制IFN‐γ依赖抗感染机制的研究

弓形虫在免疫抑制病人及胎儿感染中引起严重疾病甚至死亡，感染鼠细胞后通过TgROP18使宿主细胞IRGs磷酸化来实现免疫逃避，感染人细胞后的免疫逃避机制还不明了。前期我们发现ROP18可以结合人的NMI并使其磷酸化，致其转录水平及蛋白水平降低，细胞核中NMI的水平也降低。我们推断，ROP18分泌到人细胞内后与NMI结合，致其表达量下降或抑制其核转运，致使STAT1的转录活性降低，从而有效地抑制IFNγ依赖的细胞免疫。本课题拟分析ROP18是否通过降低NMI的转录水平、蛋白水平，或与NMI结合后占据或阻挡NMI与STAT1的结合位点，或使NMI发生依赖于磷酸化-泛素化-蛋白酶体的降解，致使与STAT1结合的NMI减少，进而降低STAT1招募CBP的能力，使其转录活性降低而抑制细胞免疫。本项目从ROP18与人NMI的互作出发来研究弓形虫感染后抑制IFNγ介导的细胞免疫的机制，具有理论创新的意义。

Toxoplasma gondii causes serious diseases and even death in immunosuppressed patients‘ and fetal infection. The parasite achieves immune escape after infection of murine cells through phosphorylation of Immune Related GTPases by its virulence factor ROP18，while what induces immune escape in human cells remains unclear. In previous research, we found that ROP18 could bind with human N-myc and Stat1 Interactor (NMI) and phosphorylate NMI, resulted in the decrease of transcription level and protein content of NMI in the cytoplasm, also the decrease of NMI content in the nuclear. We proposed that ROP18 bound to NMI after its secretion into human cells, which resulted in decreased protein level or inhibited nuclear transportation of NMI. Consequently, the transcriptional activity of STAT1 was inhibited, which effectively inhibited the IFN-gamma dependent cellular immunity. This research intended to analyze whether ROP18 inhibited human cellular immunity after T. gondii infection through decreasing the transcription level or protein content of NMI in the cytoplasm, occupying the binding site or blocking the binding of NMI with STAT1 after it combined with NMI, or through the NMI dependent phosphorylation-ubiquitination-proteasome degradation, all of which would reduce the level of NMI combined with STAT1 in the nuclear, thereby reduce the ability of STAT1 to recruit CBP and eventually its transcriptional activity. It is a novel perspective to study the mechanism of inhibiting IFN-gamma mediated cellular immunity after Toxoplasma gondii infection in human cells based on the interaction of ROP18 with human NMI.