校正淋巴细胞计数对提高基于结核抗原特异性外周血定量T细胞检测（T-SPOT.(®)TB和QFT-GIT）敏感性的影响

Impact of correcting the lymphocyte count to improve the sensitivity of TB antigen-specific peripheral blood-based quantitative T cell assays (T-SPOT.(®)TB and QFT-GIT).

作者信息

van Zyl-Smit Richard N, Lehloenya Rannakoe J, Meldau Richard, Dheda Keertan

机构信息

1 Lung Infection and Immunity Unit, Division of Pulmonology & UCT Lung Institute, Department of Medicine, 2 Division of Dermatology, Department of Medicine, 3 Institute of Infectious Diseases and Molecular Medicine, University of Cape Town, Cape Town, South Africa ; 4 Department of Infection, University College London Medical School, London, UK.

出版信息

J Thorac Dis. 2016 Mar;8(3):482-9. doi: 10.21037/jtd.2016.02.65.

DOI:10.21037/jtd.2016.02.65

PMID:27076944

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC4805805/

Abstract

BACKGROUND

The standardized blood-based TB antigen-specific T cell assay, T-SPOT.(®)TB, is 10% more sensitive than QuantiFERON(®)-TB-GIT (QFT-GIT) in detecting presumed latent TB infection (LTBI). Whilst T-SPOT.(®)TB uses a fixed number of lymphocytes per well, QFT-GIT uses a fixed volume of blood (1 mL). However, the person-to-person lymphocyte count can vary by 2 to 3 fold. We hypothesized that this variability could explain the reduced sensitivity of QFT-GIT. The findings could have potential implications for improving case detection.

METHODS

T-SPOT.(®)TB was compared to QFT-GIT readouts before and after normalization of lymphocyte count (by adjusting the blood volume or lymphocyte enrichment within a fixed 1 mL volume) to an arbitrary value of 2.5×10(6) cells/mL. Within-test variability was evaluated to meaningfully interpret results.

RESULTS

In patient-specific optimization experiments IFN-γ concentrations significantly increased when QFT-GIT positive samples were enriched with increasing concentrations of lymphocytes (1×10(6) vs. 2.5×10(6) cells/mL). However, for the group as a whole lymphocyte enrichment whilst maintaining a ~1 mL volume, compared to un-enriched samples, did not significantly increase IFN-γ [median (range): 0.03 (0-4.41) vs. 0.20 (0-2.40) IU/mL; P=0.64]. There was also no increase in IFN-γ readouts when QFT-GIT lymphocyte numbers were corrected (to 2.5×10(6) lymphocytes/mL) using volume adjustment. Interestingly, adjusted values were significantly lower than unadjusted ones [median (range): 0.02 (0-12.93) vs. 0.09 (0-14.23) IU/mL; P=0.008].

CONCLUSIONS

In QFT-GIT negative subjects lymphocyte enrichment did not increase QFT-GIT positivity rates. The reduced clinical sensitivity of the QFT-GIT assay, compared to T-SPOT.(®)TB, is likely to be due to factors other than lymphocyte count alone. Further studies are required to clarify these findings.

摘要

背景

标准化的基于血液的结核分枝杆菌抗原特异性T细胞检测方法T-SPOT.(®)TB在检测疑似潜伏性结核感染（LTBI）方面比QuantiFERON(®)-TB-GIT（QFT-GIT）敏感约10%。T-SPOT.(®)TB每孔使用固定数量的淋巴细胞，而QFT-GIT使用固定体积的血液（约1 mL）。然而，人与人之间的淋巴细胞计数可能相差2至3倍。我们推测这种变异性可能解释了QFT-GIT敏感性降低的原因。这些发现可能对改善病例检测具有潜在意义。

方法

在将淋巴细胞计数（通过调整血液体积或在固定的1 mL体积内进行淋巴细胞富集）标准化至任意值2.5×10⁶个细胞/mL之前和之后，将T-SPOT.(®)TB与QFT-GIT的检测结果进行比较。评估试验内变异性以有意义地解释结果。

结果

在患者特异性优化实验中，当QFT-GIT阳性样本中淋巴细胞浓度增加时（1×10⁶个细胞/mL对2.5×10⁶个细胞/mL），IFN-γ浓度显著增加。然而，对于整个组而言，在保持约1 mL体积的同时进行淋巴细胞富集，与未富集样本相比，并未显著增加IFN-γ[中位数（范围）：0.03（0 - 4.41）对0.20（0 - 2.40）IU/mL；P = 0.64]。当使用体积调整将QFT-GIT淋巴细胞数量校正至2.5×10⁶个淋巴细胞/mL时，IFN-γ读数也没有增加。有趣的是，校正后的值显著低于未校正的值[中位数（范围）：0.02（0 - 12.93）对0.09（0 - 14.23）IU/mL；P = 0.008]。