The role of flow cytometry in the interferon-gamma-based diagnosis of active tuberculosis and its coinfection with HIV-1--A technically oriented review

Peripheral immune cells in NAFLD patients: A spyhole to disease progression

Nonalcoholic fatty liver disease (NAFLD) is a worldwide leading cause of chronic liver disease, but we still lack ideal non-invasive tools for diagnosis and evaluation of nonalcoholic steatohepatitis (NASH) and related liver fibrosis in NAFLD population. Systemic immune dysregulations such as metabolic inflammation are believed to play central role in the development of NAFLD, signifying the hope of utilizing quantitative and phenotypic changes in peripheral immune cells among NAFLD patients as a diagnostic tool of NASH and fibrosis. In this review, we summarize the known changes in peripheral immune cells from NAFLD/NASH patients and their potential relationship with NAFLD and NASH progression. Potential challenges and possible solutions for further clinical translation are also discussed.

Combinatorial Immunoprofiling in Latent Tuberculosis Infection. Toward Better Risk Stratification

RATIONALE

Most immunocompetent patients diagnosed with latent tuberculosis infection (LTBI) will not progress to tuberculosis (TB) reactivation. However, current diagnostic tools cannot reliably distinguish nonprogressing from progressing patients a priori, and thus LTBI therapy must be prescribed with suboptimal patient specificity. We hypothesized that LTBI diagnostics could be improved by generating immunomarker profiles capable of categorizing distinct patient subsets by a combinatorial immunoassay approach.

OBJECTIVES

A combinatorial immunoassay analysis was applied to identify potential immunomarker combinations that distinguish among unexposed subjects, untreated patients with LTBI, and treated patients with LTBI and to differentiate risk of reactivation.

METHODS

IFN-γ release assay (IGRA) was combined with a flow cytometric assay that detects induction of CD25(+)CD134(+) coexpression on TB antigen-stimulated T cells from peripheral blood. The combinatorial immunoassay analysis was based on receiver operating characteristic curves, technical cut-offs, 95% bivariate normal density ellipse prediction, and statistical analysis. Risk of reactivation was estimated with a prediction formula.

MEASUREMENTS AND MAIN RESULTS

Sixty-five out of 150 subjects were included. The combinatorial immunoassay approach identified at least four different T-cell subsets. The representation of these immune phenotypes was more heterogeneous in untreated patients with LTBI than in treated patients with LTBI or unexposed groups. Patients with IGRA(+) CD4(+)CD25(+)CD134(+) T-cell phenotypes had the highest estimated reactivation risk (4.11 ± 2.11%).

CONCLUSIONS

These findings suggest that immune phenotypes defined by combinatorial assays may potentially have a role in identifying those at risk of developing TB; this potential role is supported by risk of reactivation modeling. Prospective studies will be needed to test this novel approach.

Diagnosis of latent tuberculosis infection with T-SPOT(®).TB in a predominantly immigrant population with rheumatologic disorders

PURPOSE

The objective of this study is to compare how likely positive tuberculin skin test (TST) and T-SPOT(®).TB (TSPOT) results predict risk factors for tuberculosis in a predominantly immigrant patient population at risk of latent TB infection (LTBI) and with rheumatologic conditions requiring immunomodulatory therapy (IMT).

METHODS

Prospective study conducted at a referral rheumatology clinic. Inclusion criteria included patients on various IMT, including immunosuppressive drugs that could predispose to TB progression. We studied risk factors associated with LTBI, test results, and tests' agreement.

RESULTS

We studied 101 patients. Eighty (79.2 %) were from countries where TB is prevalent and Bacille Calmette-Guérin vaccination is placed routinely. Seventy-four (73.3 %) had rheumatoid arthritis and 92 (90.7 %) were on IMT. Among patients with both TST and TSPOT results, 25 (30.9 %) were TST(+) and 20 (24.7 %) had TSPOT(+) results. Fifteen patients (18.5 %) had TST(+)/TSPOT(+) results, and 51 (63.0 %) had TST(-)/TSPOT(-) results (agreement = 81.5 %; kappa = .54 [95 % CI, .34-.74; P < .001]). Each TSPOT(+) and TST(+) results were independently associated with immigrant status and prior residence in a TB prevalent country after adjustment for immunosuppressive therapy: Adjusted OR(TSPOT+)=6.6 (95 % CI, 1.2-123.3; P = .027); and adjusted OR(TST+)=11.2 (95 % CI, 2.0-209.5; P = .003). Seven out of 10 TST(+)/TSPOT(-) cases had a TST ≥15 mm induration, including three cases with history of TST conversion.

CONCLUSIONS

TST(+) and TSPOT(+) results predict risk factors associated with LTBI independent of immunosuppressive IMT. Some TST(+)/TSPOT(-) results were unlikely to be false-negatives. The combined use of TST and TSPOT appears to be a reasonable diagnostic strategy to evaluate for LTBI in this population.

Comparative analysis of whole-blood interferon-γ and flow cytometry assays for detecting post-treatment immune responses in patients with active tuberculosis

BACKGROUND

Intracellular cytokine flow cytometry (ICCFC) has been explored to detect tuberculosis (TB) infections; however, there are little data regarding its use to examine the dynamic responses of Mycobacterium tuberculosis (MTB)-specific T-cells after anti-tuberculous therapy. The aim of this study was to analyze both dynamic changes in functional MTB antigen-specific T-cell subsets and interferon-gamma (IFN-γ) levels using ICCFC and the QuantiFERON-TB Gold In-Tube (QFT-IT) test, respectively, following anti-tuberculous treatment in patients with active TB.

METHODS

Twenty-six patients with active TB were enrolled in the study, and QFT-IT and ICCFC were performed simultaneously both before and after treatment. IFN-γ levels (QFT-IT test) and the numbers of IFN-γ- or tumor necrosis factor-alpha (TNF-α)-expressing T-cells (ICCFC assay) were examined after stimulation with MTB antigen.

RESULTS

There was no significant reduction in the mean IFN-γ concentrations measured by the QFT-IT test after anti-tuberculous treatment (P = 0.314). ICCFC analysis showed that the numbers of IFN-γ(+) /CD4(-) T-cells, and CD4(+) T-cells producing TNF-α, either alone or in combination with IFN-γ, were significantly reduced after anti-tuberculous treatment. The IFN-γ(+) /TNF-α(+) /CD4(+) T-cell subset showed the greatest difference between untreated and treated patients with active TB (area under the curve = 0.734, P = 0.004).

CONCLUSIONS

Unlike the QFT-IT test, ICCFC provides diverse immunological information about dynamic changes in the number of MTB antigen-specific T-cells following anti-tuberculous therapy. Thus, analysis of MTB antigen-stimulated T-cell responses using ICCFC might have a role to play in monitoring treatment responses in patients with active TB.

Comparison of whole-blood interferon-γ assay and flow cytometry for the detection of tuberculosis infection

OBJECTIVE

Limited data exist about the performance of the intracellular cytokine flow cytometry (ICCFC) with respect to that of the commercial interferon-γ release assay for the detection of tuberculosis (TB) infection. Here, we compared the diagnostic accuracy of an ICCFC with that of the QuantiFERON-TB Gold In-Tube (QFT-IT) test for the detection of TB in a clinical setting.

METHODS

Eighty-nine patients suspected of having TB were prospectively included. Both the QFT-IT test and ICCFC were performed for all subjects (TB [n = 65] and non-TB [n = 24]). Ten healthy controls who tested negative by QFT-IT were also assessed by ICCFC.

RESULTS

The sensitivity of the ICCFC was significantly superior to that of the QFT-IT test (91% vs. 78%, p = 0.021). The clinical characteristics of patients in whom the ICCFC exhibited superior sensitivity compared to the QFT-IT test included advanced age, lymphocytopenia, hypoalbuminemia, increased C-reactive protein level, a positive acid-fast bacilli smear of respiratory specimens, and radiographically more extensive disease.

CONCLUSIONS

ICCFC might be a preferable technique for the detection of TB infection, particularly in patients with conditions associated with impaired performance of the QFT-IT test.

Pulmonary immune-compartment-specific interferon gamma responses in HIV-infected individuals with active tuberculosis (TB) in an area of high TB prevalence

There is a paucity of data on the pulmonary immune-compartment interferon gamma (IFNγ) response to M. tuberculosis, particularly in settings of high tuberculosis (TB) prevalence and in HIV-coinfected individuals. This data is necessary to understand the diagnostic potential of commercially available interferon gamma release assays (IGRAs) in both the pulmonary immune-compartment and peripheral blood. We used intracellular cytokine staining by flow cytometry to assess the IFNγ response to purified protein derivative (PPD) and early secretory antigen 6 (ESAT6) in induced sputa (ISp) and blood samples from HIV-infected, smear-negative, TB suspects. We found that individuals with active TB disease produced significantly less IFNγ in response to PPD in their induced sputa samples than individuals with non-active TB (control group). This difference was not reflected in the peripheral blood, even within the CD27- CD4+ memory T lymphocyte population. These findings suggest that progression to active TB disease may be associated with the loss of IFNγ secretion at the site of primary infection. Our findings highlight the importance of studying pulmonary immune-compartment M. tuberculosis specific responses to elucidate IFNγ secretion across the spectrum of TB disease.

Flow cytometry of sputum: assessing inflammation and immune response elements in the bronchial airways

BACKGROUND

The evaluation of sputum leukocytes by flow cytometry (FCM) is an opportunity to assess characteristics of cells residing in the central airways, yet it is hampered by certain inherent properties of sputum including mucus and large amounts of contaminating cells and debris.

OBJECTIVE

To develop a gating strategy based on specific antibody panels in combination with light scatter properties for flow cytometric evaluation of sputum cells.

METHODS

Healthy and mild asthmatic volunteers underwent sputum induction. Manually selected mucus "plug" material was treated with dithiothreitol, filtered and total leukocytes acquired. Multicolor FCM was performed using specific gating strategies based on light scatter properties, differential expression of CD45 and cell lineage markers to discriminate leukocytes from squamous epithelial cells and debris.

RESULTS

The combination of forward scatter and CD45 expression reliably segregated sputum leukocytes from contaminating squamous epithelial cells and debris. Overlap of major leukocyte populations (neutrophils, macrophages/monocytes) required the use of specific antibodies (e.g. CD16, CD64, CD14, HLA-DR) that differentiated granulocytes from monocytes and macrophages. These gating strategies allowed identification of small populations of eosinophils, CD11c+ myeloid dendritic cells, B-cells and natural killer cells.

CONCLUSIONS

Multicolor FCM can be successfully applied to sputum samples to identify and characterize leukocyte populations residing on the surfaces of the central airways.

CLINICAL RELEVANCE

This research describes detailed methods to overcome difficulties associated with FCM of sputum samples, which previously has been lacking in the literature. FCM of sputum samples can provide valuable information on inflammation and immunological response elements in the bronchial airways for both clinical diagnostic and research applications and can be a useful tool in inhalation toxicology for assessing health effects of inhaled environmental pollutants.

Laboratory diagnosis of tuberculosis in resource-poor countries: challenges and opportunities

With an estimated 9.4 million new cases globally, tuberculosis (TB) continues to be a major public health concern. Eighty percent of all cases worldwide occur in 22 high-burden, mainly resource-poor settings. This devastating impact of tuberculosis on vulnerable populations is also driven by its deadly synergy with HIV. Therefore, building capacity and enhancing universal access to rapid and accurate laboratory diagnostics are necessary to control TB and HIV-TB coinfections in resource-limited countries. The present review describes several new and established methods as well as the issues and challenges associated with implementing quality tuberculosis laboratory services in such countries. Recently, the WHO has endorsed some of these novel methods, and they have been made available at discounted prices for procurement by the public health sector of high-burden countries. In addition, international and national laboratory partners and donors are currently evaluating other new diagnostics that will allow further and more rapid testing in point-of-care settings. While some techniques are simple, others have complex requirements, and therefore, it is important to carefully determine how to link these new tests and incorporate them within a country's national diagnostic algorithm. Finally, the successful implementation of these methods is dependent on key partnerships in the international laboratory community and ensuring that adequate quality assurance programs are inherent in each country's laboratory network.

Flow cytometric measurements of TB-specific T cells comparing with QuantiFERON-TB gold

BACKGROUND

Interferon-gamma (IFN-gamma) release assays and the detection of IFN-gamma synthesis in the cytoplasm of activated CD4+ T cells by flow cytometry have recently been used for tuberculosis (TB) diagnosis. The aim of this study was to compare the performance of IFN-gamma assay between ELISA (QuantiFERON-TB Gold, QFT) and intracellular cytokine flow cytometry (ICCFC), and to investigate the significance of an optimal gating strategy in ICCFC.

METHODS

The CD4+ T cell response to TB antigens was measured using the intracellular cytokine staining technique and four color FC (CD3, CD4, IFN-gamma, and tumor necrosis factor-alpha (TNF-alpha)) on whole blood samples. The results were compared with those of QFT.

RESULTS

Regarding sensitivity in the TB group, patients in the QFT positive TB group (N = 22) were all ICCFC positive and 9 patients (64%) in the QFT negative TB group (N = 14) were ICCFC positive. In all test tubes (N = 72), sensitivity of "targeted" gating for TNF-alpha+ IFN-gamma+ CD4+ T cells was significantly higher than customary gating (72%, 54%, respectively, P = 0.001).

CONCLUSIONS

The diagnostic sensitivity of ICCFC was further confirmed to be much higher than that of QFT. In the ICCFC analysis, TNF-alpha+ IFN-gamma+ CD4+ T cells should be sequentially gated through appropriately defined regions, minimizing interferents and reflecting characteristics of light scatter and marker expressions of CD4+ T cells activated by TB antigens.

Harmonization guidelines for HLA-peptide multimer assays derived from results of a large scale international proficiency panel of the Cancer Vaccine Consortium

Purpose

The Cancer Vaccine Consortium of the Cancer Research Institute (CVC-CRI) conducted a multicenter HLA-peptide multimer proficiency panel (MPP) with a group of 27 laboratories to assess the performance of the assay.

Experimental design

Participants used commercially available HLA-peptide multimers and a well characterized common source of peripheral blood mononuclear cells (PBMC). The frequency of CD8+ T cells specific for two HLA-A2-restricted model antigens was measured by flow cytometry.

The panel design allowed for participants to use their preferred staining reagents and locally established protocols for both cell labeling, data acquisition and analysis.

Results

We observed significant differences in both the performance characteristics of the assay and the reported frequencies of specific T cells across laboratories. These results emphasize the need to identify the critical variables important for the observed variability to allow for harmonization of the technique across institutions.

Conclusions

Three key recommendations emerged that would likely reduce assay variability and thus move toward harmonizing of this assay. (1) Use of more than two colors for the staining (2) collect at least 100,000 CD8 T cells, and (3) use of a background control sample to appropriately set the analytical gates. We also provide more insight into the limitations of the assay and identified additional protocol steps that potentially impact the quality of data generated and therefore should serve as primary targets for systematic analysis in future panels. Finally, we propose initial guidelines for harmonizing assay performance which include the introduction of standard operating protocols to allow for adequate training of technical staff and auditing of test analysis procedures.

Electronic supplementary material

The online version of this article (doi:10.1007/s00262-009-0681-z) contains supplementary material, which is available to authorized users.

How flow cytometry is changing the study of TB immunology and clinical diagnosis

The application of flow cytometry has hugely advanced the field of tuberculosis (TB) across all areas of research ranging from diagnostic tests to understanding the underlying immunology. As cellular responses are understood to be the mainstay of the immune response in the control of TB it is very likely that polychromatic flow will become the tool of choice for assessing the effects of vaccination. Results are particularly encouraging in this area. The development of a new type of diagnostic test, a prototype of which has been reported, may be the spin-off of a broad and systematic approach to understanding and profiling the T-cell response to TB. It is obvious that flow cytometry will not be able to address all research questions in the field of TB. However, its enormous flexibility as a technology will make it the tool of choice in many situations. An ever increasing availability of flow cytometers, even in resource-poor countries, will rapidly change the face of TB research and management in the years ahead.