Singhal Amit, Jaiswal Anand, Arora Virendra K, Prasad Hanumanthappa K
TB Immunology Laboratory, Department of Biotechnology, All India Institute of Medical Sciences, New Delhi 110029, India.
Infect Immun. 2007 May;75(5):2500-10. doi: 10.1128/IAI.01743-06. Epub 2007 Mar 5.
Mycobacterium tuberculosis inhibits gamma interferon (IFN-gamma)-mediated antimycobacterial action by adopting diverse mechanisms. IFN-gamma binds to its receptor, IFN-gammaR, in order to initiate proper signaling. We have observed reduced surface expression levels of IFN-gamma receptor 1 (IFN-gammaR1) in untreated pulmonary tuberculosis patients compared to those in healthy individuals (P < 0.01). Following antitubercular therapy, the expression of IFN-gammaR1 was restored in these patients. To delineate the mechanism by which M. tuberculosis modulates IFN-gammaR1, in vitro experiments were designed, wherein the down modulation of IFN-gammaR1 surface expression was observed for CD14+ cells in peripheral blood mononuclear cells (PBMCs) cocultured with live M. tuberculosis compared to that for uninfected cells (P < 0.01). No modulation of IFN-gammaR1 expression was observed for CD14+ cells in PBMCs infected with Mycobacterium smegmatis. A time-dependent decrease in IFN-gammaR1 mRNA expression was observed for PBMCs infected with M. tuberculosis. Similar down modulation of IFN-gammaR1 protein and mRNA expression in phorbol myristate acetate-differentiated THP-1 cells (pdTHP-1) by M. tuberculosis was observed (P < 0.01). Using reporter gene analysis of 5' deletion constructs of the IFN-gammaR1 gene (IFNGR1) promoter, the decrease in IFN-gammaR1 mRNA in M. tuberculosis-infected pdTHP-1 cells was shown to be due to the decreased transcription of IFNGR1. By immunoblotting and electrophoretic mobility shift assays, the down regulation of stimulating protein 1 (Sp1) expression and its recruitment on the phorbol ester-responsive element of the IFNGR1 promoter in M. tuberculosis-infected pdTHP-1 cells was observed. This down regulation of Sp1 in pdTHP-1 cells cocultured with M. tuberculosis may be responsible for the down regulation of IFN-gammaR1 expression, thereby potentially altering its receptivity to IFN-gamma.
结核分枝杆菌通过多种机制抑制γ干扰素（IFN-γ）介导的抗分枝杆菌作用。IFN-γ与其受体IFN-γR结合，以启动适当的信号传导。我们观察到，未经治疗的肺结核患者中IFN-γ受体1（IFN-γR1）的表面表达水平低于健康个体（P < 0.01）。抗结核治疗后，这些患者中IFN-γR1的表达得以恢复。为了阐明结核分枝杆菌调节IFN-γR1的机制，我们设计了体外实验，结果发现，与未感染细胞相比，外周血单核细胞（PBMC）中与活结核分枝杆菌共培养的CD14+细胞的IFN-γR1表面表达下调（P < 0.01）。感染耻垢分枝杆菌的PBMC中的CD14+细胞未观察到IFN-γR1表达的调节。感染结核分枝杆菌的PBMC中观察到IFN-γR1 mRNA表达呈时间依赖性下降。结核分枝杆菌对佛波酯分化THP-1细胞（pdTHP-1）中IFN-γR1蛋白和mRNA表达的下调作用类似（P < 0.01）。通过对IFN-γR1基因（IFNGR1）启动子的5'缺失构建体进行报告基因分析表明，结核分枝杆菌感染的pdTHP-1细胞中IFN-γR1 mRNA的减少是由于IFNGR1转录减少所致。通过免疫印迹和电泳迁移率变动分析，观察到结核分枝杆菌感染的pdTHP-1细胞中刺激蛋白1（Sp1）表达下调及其在IFNGR1启动子的佛波酯反应元件上募集减少。与结核分枝杆菌共培养的pdTHP-1细胞中Sp1的这种下调可能是IFN-γR1表达下调以及潜在改变其对IFN-γ反应性的原因。
