Pai M
Division of Epidemiology, University of California, Berkeley, CA 94720, and Division of Pulmonary & Critical Care Medicine, San Francisco General Hospital, University of California, San Francisco, USA.
Indian J Med Microbiol. 2005 Jul;23(3):151-8. doi: 10.4103/0255-0857.16585.
For nearly a century, there were no alternatives to the tuberculin skin test (TST) for diagnosing latent tuberculosis infection. Because of advances in immunology and genomics, for the first time, an alternative has emerged in the form of T cell based interferon-g (IFN-gamma) assays, a new generation of in vitro tests of cellular immunity. These assays measure cell mediated immune response by quantifying IFN-gamma released by T cells in response to stimulation by Mycobacterium tuberculosis antigens. Although early versions of IFN-gamma assays used purified protein derivative (PPD) as the stimulating antigen, newer versions use antigens that are significantly more specific to M. tuberculosis. These specific antigens include ESAT-6 and CFP-10. These proteins, encoded by genes located within the region of difference 1 (RD1) segment of the M. tuberculosis genome, are more specific to M. tuberculosis than PPD because they are not shared with any BCG substrains or several nontuberculous mycobacterial species. A review of current evidence on the performance of IFN-gamma assays and TST suggests that both the TST and IFN-gamma assays have advantages and limitations, and both tests appear to be useful at this time. The emergence of IFN-gamma assays is a much anticipated, welcome development that has, for the first time, increased the choice of tests available for diagnosing latent tuberculosis infection. Because both tests have their strengths and limitations, the decision to select one over the other will depend on the population, the goal of testing, and the resources available. To fully evaluate the utility of IFN-gamma assays in high burden countries such as India, long-term cohort studies are needed to determine the association between positive IFN-gamma results and the subsequent risk of active disease.
近一个世纪以来，结核菌素皮肤试验（TST）一直是诊断潜伏性结核感染的唯一方法。由于免疫学和基因组学的进展，基于T细胞的干扰素-γ（IFN-γ）检测作为一种替代方法首次出现，这是新一代的细胞免疫体外检测方法。这些检测通过量化T细胞在结核分枝杆菌抗原刺激下释放的IFN-γ来测量细胞介导的免疫反应。尽管早期版本的IFN-γ检测使用纯化蛋白衍生物（PPD）作为刺激抗原，但新版本使用的抗原对结核分枝杆菌的特异性要高得多。这些特异性抗原包括ESAT-6和CFP-10。这些蛋白质由结核分枝杆菌基因组差异区域1（RD1）片段中的基因编码，比PPD对结核分枝杆菌更具特异性，因为它们不会与任何卡介苗亚菌株或几种非结核分枝杆菌共有。对当前关于IFN-γ检测和TST性能的证据进行的综述表明，TST和IFN-γ检测都有优点和局限性，目前这两种检测似乎都很有用。IFN-γ检测的出现是一项备受期待的、令人欢迎的进展，它首次增加了可用于诊断潜伏性结核感染的检测选择。由于两种检测都有其优势和局限性，选择其中一种检测的决定将取决于人群、检测目的和可用资源。为了全面评估IFN-γ检测在印度等高负担国家的效用，需要进行长期队列研究，以确定IFN-γ检测结果阳性与随后发生活动性疾病风险之间的关联。
