Original ArticleLymphocyte subset analysis in QuantiFERON-TB Gold Plus and T-Spot.TB for latent tuberculosis infection in rheumatoid arthritis☆
Introduction
Rheumatoid arthritis (RA) is an immune mediated inflammatory disorder, and immune suppressive drugs, like steroid, methotrexate (MTX) and biological agents etc, are prescribed. RA patients receiving treatments are in a kind of immunosuppressive condition that presents increased risk of developing active tuberculosis (TB) [1]. The introduction of biological agents, such as tumor necrosis factor (TNF) inhibitors, boosts the risk still more [2], [3]. Active TB is believed to develop due to reactivation of latent tuberculosis infection (LTBI) [2], [4], [5]. Japan College of Rheumatology published guideline and recommends interferon-γ release assay (IGRA) or tuberculin skin test to screen TB infection before the initiation of MTX and biological agent.
Therefore, accurate diagnosis of LTBI, followed by appropriate isoniazid therapy, is recommended for RA patients [6].
LTBI is defined in World Health Organization Guidelines as a state of persistent immune response to stimulation by Mycobacterium tuberculosis (M. tuberculosis) antigens without evidence of clinically manifested active TB [7]. Interferon-γ release assays (IGRAs) estimate cell-mediated immune response to TB-specific antigens like ESAT-6 and CFP-10. IGRAs have been key tools for LTBI diagnosis. Two IGRAs, QuantiFERON®-TB Gold in Tube (QFT-GIT) (Cellestis/Qiagen, Carnegie, Australia) and T-Spot®.TB (TSPOT) (Oxford Immunotec, Abingdon, United Kingdom), are available [8], [9], [10]. Immune response is thought to be attenuated in an immunosuppressive condition like RA. The sensitivity of IGRAs would decrease in RA, and could LTBI not be detected sufficiently [11], [12], [13].
QuantiFERON®-TB Gold Plus (QFT-Plus) has been available as the 4th generation QuantiFERON. QFT-Plus uses two tubes, TB1 and TB2. TB1 is designed to elicit a CD4 T-cell response, like the current QFT-GIT. TB2 was newly designed to elicit immune response driven by both CD4 T-cell and CD8 T-cell. CD8 T-cell response is expected to increase the sensitivity for LTBI detection. Especially, CD8 T-cell work at the early phase of M. tuberculosis infection and at a phase of reactivation from LTBI [14], [15], [16], [17]. Therefore, lymphocyte subsets might affect the immune response in IGRAs, especially in QFT-Plus.
The objectives of this study are to compare the performance of two IGRAs, QFT-Plus and TSPOT, for LTBI diagnosis in RA patients, and to evaluate the influence of CD4 T-cell and CD8 T-cell counts on the immune responses to IGRAs.
Section snippets
Study design and settings
This study was a cross-sectional analysis conducted at the National Hospital Organization Chiba-East Hospital (CEH) in Japan. A total of 154 RA patients were enrolled between April and August 2016. We included stable RA patients who had received current therapy for more than 3 months. Patient characteristics are described in Table 1. Biological agents were introduced to 82 patients (53.9%). They consisted of infliximab, etanercept, adalimumab, golimumab, certolizumab pegol, tocilizumab and
Results
The results of QFT-Plus and TSPOT are shown in Table 2. The numbers of QFT-Plus diagnosis of positive, negative and indeterminate were 15, 138 and one, respectively; their percentages were 9.7% (95% Confidence Interval (CI), 6.0–15.4), 90.2% (95% CI, 84.6–94.1) and 1.0% (95% CI, 0.1–3.6). The numbers of TSPOT diagnosis of positive, negative and indeterminate were 7, 143 and 4, respectively; their percentages were 4.5% (95% CI, 2.2–9.1), 92.9% (95% CI, 87.7–96.0) and 2.6% (95% CI, 1.0–6.5).
Discussion
This is the first study to compare QFT-Plus and TSPOT, with association with lymphocyte subsets in RA. QFT-Plus, the 4th generation QuantiFERON, has been expected to increase the sensitivity of LTBI diagnosis by introduction of TB2, which can estimate both CD4 T-cell and CD8 T-cell immune response. TB1 in QFT-Plus and TSPOT just estimate the CD4 T-cell response. The positivity rates of QFT-Plus and TSPOT were 9.7% and 4.5%, respectively. QFT-Plus demonstrated significantly higher positivity
Conflicts of interest
None declared.
Acknowledgement
This research was supported by the Research Program on Emerging and Re-emerging Infectious Diseases from the Japan Agency for Medical Research and Development, AMED (Grant number 15fk0108004h0001 and 16fk0108204h0002).
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All authors meet the ICMJE authorship criteria.