Comparison of a whole-blood interferon-gamma assay and tuberculin skin testing in patients with active tuberculosis and individuals at high or low risk of Mycobacterium tuberculosis infection

BACKGROUND: QuantiFeron-TB (QIFN) is a whole-blood interferon-;gamma assay for the recognition of cell-mediated immune response to Mycobacterium tuberculosis infection. OBJECTIVES: To compare the QIFN assay with the tuberculin skin test (TST) in patients with newly diagnosed culture-proven tuberculosis (TB) and healthy volunteers with high or low risk of latent M tuberculosis infection and to identify factors associated with discordance between tests. METHOD: Two-hundred fifty-eight subjects underwent both assays. All participants completed a detailed questionnaire, and data from TB patients' medical records were collected. RESULTS: In the entire study population, agreement between tests was moderate and the correlation between the magnitude of QIFN response and the TST induration diameter was significant. In volunteers with no known risk of exposure to M tuberculosis, the specificity of the assays was comparable. However, in subjects with active TB or those vaccinated with bacille Calmette-Guérin, the QIFN assay detected more reactors than did the TST. In these individuals, agreement between assays was poor and no correlation or only a weak correlation was found between the diameter of TST induration and the magnitude of the interferon-gamma responses. CONCLUSIONS: The sensitivity of the QIFN assay is greater than that of the TST in patients with active TB before the initiation of anti-TB chemotherapy, but its specificity is influenced more by bacille Calmette-Guérin vaccination. The QIFN assay may provide an improvement over the current practice of the use of the TST to support diagnosis of active M tuberculosis infection in the clinic; however, QIFN cannot be considered an adequate replacement for the TST in the screening for latent infection.     

Comparison of two commercial interferon-gamma assays for diagnosing Mycobacterium tuberculosis infection.

The clinical usefulness of ex vivo interferon-gamma assays may largely depend on the assay format and epidemiological status of tuberculosis (TB) in the region studied. From July 2004 to June 2005 a prospective comparison study was undertaken at a tertiary referral hospital in South Korea. The results of tuberculin skin tests (TST) and the commercially available QuantiFERON-TB Gold (QFT-G) and T SPOT-TB (SPOT) assays were compared in an intermediate TB-burden country. Of the 224 participants studied, results from all three tests (TST, QFT-G, and SPOT) were available in 218; 87 with active TB and 131 at a low risk for TB. Using 10 mm as a cut-off for TST, SPOT sensitivity (96.6%) was significantly higher than that seen for TST (66.7%) and QFT-G (70.1%). QFT-G showed superior specificity over TST (91.6 versus 78.6%). Although the specificity of QFT-G was higher than that of SPOT (91.6 versus 84.7%), the difference was not statistically significant. Whilst some differences were found in the performance of the two commercialised interferon-gamma assays, they seemed to be superior in their detection of Mycobacterium tuberculosis infection compared with tuberculin skin tests. The most appropriate choice of interferon-gamma assay to use may depend on the clinical setting.     

Mycobacterium tuberculosis produces pili during human infection

Mycobacterium tuberculosis is responsible for nearly 3 million human deaths worldwide every year. Understanding the mechanisms and bacterial factors responsible for the ability of M. tuberculosis to cause disease in humans is critical for the development of improved treatment strategies. Many bacterial pathogens use pili as adherence factors to colonize the host. We discovered that M. tuberculosis produces fine (2- to 3-nm-wide), aggregative, flexible pili that are recognized by IgG antibodies contained in sera obtained from patients with active tuberculosis, indicating that the bacilli produce pili or pili-associated antigen during human infection. Purified M. tuberculosis pili (MTP) are composed of low-molecular-weight protein subunits encoded by the predicted M. tuberculosis H37Rv ORF, designated Rv3312A. MTP bind to the extracellular matrix protein laminin in vitro, suggesting that MTP possess adhesive properties. Isogenic mtp mutants lost the ability to produce Mtp in vitro and demonstrated decreased laminin-binding capabilities. MTP shares morphological, biochemical, and functional properties attributed to bacterial pili, especially with curli amyloid fibers. Thus, we propose that MTP are previously unidentified host-colonization factors of M. tuberculosis.     

Rapid diagnosis of Mycobacterium tuberculosis infection in children using interferon-gamma release assays (IGRAs)

Diagnosis of tuberculosis (TB) in children by the tuberculin skin test (TST) poses a diagnostic challenge for physicians due to its low specificity and cross-reactivity with nontuberculous mycobacteria and bacille Calmette-Guerin (BCG). Although interferon-gamma release assays (IGRAs) have been shown as novel TST alternatives for diagnosis of latent TB infection (LTBI) in adults, their effectiveness is less clear in children. The present study examined QuantiFERON-TB Gold (QFT-G) responses and IFN-gamma production capacity of TST-positive children, younger children ≤5 years. A total of 517 children of whom 434 were TST positive ranging in age from 1 month to 18 years were evaluated by the QFT-G. Of the 517 children, 434 (84%) were TST positive, 25 (5.8%) of whom were found to be QFT-G positive and 25 (5.4%) with an indeterminate response. Of the 517 children, 355 (68.7%) were previously BCG immunized and 310/355 (87.3%) were TST positive including 18/27 (66.7%) QFT-positive children. Adequate IFN-gamma production by purified TB peptides or mitogen was observed in 92.8% of children, 29.6% of whom were <5 years. This study shows that the QFT-G assay is useful for diagnosis of LTBI. The finding of 5.8% positive QFT-G in 434 TST-positive children underscores the superior specificity of the QFT-G than the TST and its greater cost effectiveness in preventing unnecessary and potentially toxic treatment in children. The study suggests that the majority of positive TST in children represent false-positive reactions and supports the use of IGRAs for diagnosis of LTBI in children, including those <5 years of age.     

抗原刺激后外周血单个核细胞γ干扰素释放反应在结核分枝杆菌感染和结核病诊断中的意义

目的 探讨3种结核分枝杆菌抗原刺激后外周血单个核细胞（PBMC）γ干扰素（IFN-γ）释放反应对结核性感染和结核病的诊断意义。方法 获取活动性结核病患者（结核组，57例）、肺癌患者（肺癌组，29例）和健康人（健康对照组，27名）外周血单个核细胞。分别将结核分枝杆菌纯蛋白衍生物（PPD）、结核分枝杆菌早期分泌抗原靶6000蛋白（ESAT6）和38000抗原与PBMC共培养5d，采用酶联免疫吸附测定（ELISA）法检测培养上清液中IFN-γ浓度。比较3种抗原PBMC IFN-γ释放水平和PPD皮试（TST）结果。结果 （1）健康对照组：TST反应与BCG接种史及排菌患者接触密切程度经Logistic回归分析显示均呈正相关（P=0．047和P=0．041）；以ESAT6为抗原的PBMC IFN-γ释放水平与结核病患者接触密切程度相关（P=0．005），而与BCG接种史无明显相关性。（2）3组间TST结果差异无显著性。（3）以38000抗原刺激后IFN-1释放水平为观察指标，经受试者操作特性（ROC）曲线分析获得最佳域值为1000pg／ml，以此判断38000抗原刺激后IFN-γ释放水平诊断结核病敏感性为64．9％，特异性为89．3％，准确性为77．0％，阳性预测值为86．0％，阴性预测值为71．0％。结论 ESAT6抗原的IFN-γ释放反应对结核分枝杆菌感染的诊断意义优于TST，38000抗原刺激后IFN-γ释放反应对结核病的临床诊断有辅助意义。     

Usefulness of whole-blood interferon-gamma assay and interferon-gamma enzyme-linked immunospot assay in the diagnosis of active pulmonary tuberculosis

PURPOSES: The aim of this study was to evaluate the usefulness of the whole-blood interferon-gamma assay (enzyme-linked immunosorbent assay [ELISA]) and interferon-gamma enzyme-linked immunospot assay (ELISPOT) based on early secretory antigenic target 6 and culture filtrate protein 10 in the diagnosis of active pulmonary tuberculosis (TB) in routine clinical practice. METHOD: We conducted a prospective study enrolling 144 participants with suspected pulmonary TB in a tertiary referral hospital in Seoul, South Korea, to investigate the diagnostic sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of these tests. Clinical assessment, tuberculin skin test (TST), whole-blood interferon-gamma ELISA (QuantiFERON-TB Gold [QFT-G]; Cellestis Ltd; Victoria, Australia), and an ELISPOT assay (T SPOT.TB; Oxford Immunotec; Oxford, UK) were performed. Test results were compared with the final confirmed diagnoses. RESULTS: Active pulmonary TB was diagnosed in 67 of 144 participants (47%). Sensitivities of QFT-G and T SPOT.TB for active pulmonary TB were 89% (95% confidence interval [CI], 79 to 96%) and 92% (95% CI, 83 to 97%), respectively; and specificities were 49% (95% CI, 37 to 61%) and 47% (95% CI, 36 to 59%). NPVs of QFT-G (84%; 95% CI, 69 to 93%) and T SPOT.TB (87%; 95% CI, 73 to 96%) were higher than that of TST (64%; 95% CI, 51 to 76%) [p = 0.001 and p < 0.001, respectively]. CONCLUSION: High NPVs of QFT-G and T SPOT.TB for the diagnosis of active TB suggest the supplementary role of these tests for the diagnostic exclusion of active TB, although the low PPV limits their usefulness in routine clinical practice in South Korea, where the prevalence of latent TB infection is considerable.     

重组结核分枝杆菌蛋白筛查结核分枝杆菌感染的试验研究

.0,均P>0.05).38000蛋白皮肤试验阳性反应直径多为5～9 mm,PPD试验阳性反应直径多为5～14 mill.结论 38000蛋白有望用于MTB感染的筛查.     

γ-干扰素对免疫低下小鼠结核分支杆菌感染的影响

目的　观察、评价γ干扰素(IFNγ)对免疫功能低下小鼠结核分支杆菌感染的影响和疗效。方法 将DBA/2小鼠90只按免疫功能正常和免疫功能低下2种状态分别制成小鼠结核分支杆菌感染模型。随机分组给予IFNγ或IFNγ单克隆抗体治疗,检测肺组织菌落计数,观察治疗后生存率。结果 免疫正常组小鼠无死亡,第2周、第4周菌落数分别为(51.5±17.5)×10³cfu/mL、(106.3±41.0)×10³cfu/mL。免疫低下组8只死亡,菌落数分别为(163.7±61.7)×10³cfu/mL、(768.3±206.5)×10³cfu/mL,免疫低下+IFNγ组3只死亡,菌落数分别为(54.2±21.3)×10³cfu/mL、(212.7±80.7)×10³cfu/mL,免疫低下组与免疫低下+IFNγ组比较有显著性差异。免疫正常小鼠给予IFNγ抗体后肺组织菌落数增多,与对照组比较有显著性差异。结论 IFNγ增强宿主免疫功能,对结核分支杆菌感染小鼠产生保护效应,适用于免疫功能低下宿主合并结核感染的辅助治疗。     

Multidrug resistant Mycobacterium tuberculosis in patients with human immunodeficiency virus infection.

Multidrug resistant Mycobacterium tuberculosis (MDR-MTB) infection has not been recognized as a serious problem in patients with human immunodeficiency virus (HIV) infection. Multidrug resistance (MDR) has appeared in our medical center in 24 out of 72 patients between January 1990 and May 1991 compared to 8 out of 132 patients within the period from 1982 to 1987 (relative risk 5.50 with 95 percent confidence interval 2.61 to 11.61). We describe 19 patients with MDR in MTB (isoniazid and at least one additional first line drug), who had serologic evidence of HIV infection, 13 of whom were diagnosed with acquired immunodeficiency syndrome (AIDS). The MTB cultures from 10 out of 19 patients with MDR were resistant to three or more drugs. Fifteen patients died although 9 out of these 15 had received at least a four-drug regimen for a mean time of seven weeks (range 2 to 12). This increase in MDR was seen in ten homosexuals and nine intravenous drug users. This rapid appearance of MDR-MTB strains is worrisome. New strategies for empiric therapy of such patients while awaiting sensitivity data are needed.     

Relationship between whole-blood interferon-gamma responses and the risk of active tuberculosis

We have analyzed the relationship between the responses to the diagnostic method for Mycobacterium tuberculosis (Mtb) infection, QuantiFERON-TB Gold (QFT-G), and the risk of developing active tuberculosis (TB). Contacts under 42 years old who were exposed to a patient with infectious pulmonary TB were tested using QFT-G during an investigation. Among 172 contacts, 111 (64.5%) were QFT-G positive. All subjects were evaluated for active TB by chest X-ray examination and, if needed, by CT scan at the time of the QFT-G test and 39 were diagnosed with active TB based on radiological abnormalities consistent with TB. Of these, 35 (89.7%) were QFT-G positive. Statistically the geometric mean of interferon-gamma (IFN-gamma) production levels of the active TB group was significantly larger than that of the latent TB infection group (p=0.013). The results of the multivariate analysis clearly showed that a combined parameter of ESAT-6 and CFP-10 significantly contributes to disease risk for the infected subjects. Our results suggest that subjects with high levels of IFN-gamma production in response to either ESAT-6 and/or CFP-10 in the QFT-G test have a higher possibility of developing active TB than QFT-G positive subjects with lower levels of IFN-gamma.     

Exclusion of active Mycobacterium tuberculosis complex infection with the T-SPOT.TB assay.

The present brief report describes four cases with mycobacterial infection and negative T-SPOT.TB tests. This test proved to be a useful tool to help rule out the diagnosis of active Mycobacterium tuberculosis infection and could therefore prevent unnecessary or inappropriate therapy.