Incubation of whole blood at 39°C augments gamma interferon (IFN-γ)-induced protein 10 and IFN-γ responses to Mycobacterium tuberculosis antigens

Comparison of the Standard E TB-Feron ELISA and QuantiFERON-TB Gold PLUS assays: the advantageous use of whole recombinant protein antigens for latent tuberculosis diagnosis

The laboratory diagnosis of latent tuberculosis is often performed using interferon-gamma release assays. Here, we compared two enzyme-linked immunosorbent assay-based interferon-gamma release assays, namely, the newly developed Standard E TB-Feron enzyme-linked immunosorbent assay (STFE) and the QuantiFERON-TB Gold PLUS assay (QFT-GP), using samples from 155 participants. The STFE is based on using whole EAST6 and CFP10 recombinant antigens for latent tuberculosis diagnosis. The participants were classified into four groups and screened using both assays per the manufacturers' instructions. Thereafter, two statistical analyses were conducted to compare the obtained results. First, the STFE results were compared with the QTF-GP results (used as the gold standard) to calculate the total concordance, sensitivity, and specificity of STFE. Second, positivity and negativity concordances were calculated to differentiate healthy participants from participants with tuberculosis. The STFE showed 97% and 94% sensitivity and specificity, respectively. Furthermore, its positivity and negativity concordances were 91% and 98%, respectively. These results indicate the coordinated clinical performance of STFE in detecting latent tuberculosis and its improved performance in targeting tuberculosis-infected participants. Based on the comparison of the latent tuberculosis diagnostic abilities of STFE and QFT-GP, we establish the suitability and superior performance of STFE as a diagnostic tool.

Fever as an evolutionary agent to select immune complexes interfaces

We herein analyzed all available protein–protein interfaces of the immune complexes from the Protein Data Bank whose antigens belong to pathogens or cancers that are modulated by fever in mammalian hosts. We also included, for comparison, protein interfaces from immune complexes that are not significantly modulated by the fever response. We highlight the distribution of amino acids at these viral, bacterial, protozoan and cancer epitopes, and at their corresponding paratopes that belong strictly to monoclonal antibodies. We identify the “hotspots”, i.e. residues that are highly connected at such interfaces, and assess the structural, kinetic and thermodynamic parameters responsible for complex formation. We argue for an evolutionary pressure for the types of residues at these protein interfaces that may explain the role of fever as a selective force for optimizing antibody binding to antigens.

HIV-Infected Patients Developing Tuberculosis Disease Show Early Changes in the Immune Response to Novel Mycobacterium tuberculosis Antigens

Background: In individuals living with HIV infection the development of tuberculosis (TB) is associated with rapid progression from asymptomatic TB infection to active TB disease. Sputum-based diagnostic tests for TB have low sensitivity in minimal and subclinical TB precluding early diagnosis. The immune response to novel Mycobacterium tuberculosis in-vivo expressed and latency associated antigens may help to measure the early stages of infection and disease progression and thereby improve early diagnosis of active TB disease. Methods: Serial prospectively sampled cryopreserved lymphocytes from patients of the Swiss HIV Cohort Study developing TB disease ("cases") and matched patients with no TB disease ("controls") were stimulated with 10 novel Mycobacterium tuberculosis antigens. Cytokine concentrations were measured in cases and controls at four time points prior to diagnosis of TB: T1-T4 with T4 being the closest time point to diagnosis. Results: 50 samples from nine cases and nine controls were included. Median CD4 cell count at T4 was 289/ul for the TB-group and 456/ul for the control group. Viral loads were suppressed in both groups. At T4 Rv2431c-induced and Rv3614/15c-induced interferon gamma-induced protein (IP)-10 responses and Rv2031c-induced and Rv2346/Rv2347c-induced tumor necrosis factor (TNF)-α responses were significantly higher in cases compared to controls (p < 0.004). At T3 - being up to 2 years prior to TB diagnosis - Rv2031c-induced TNF-α was significantly higher in cases compared to controls (p < 0.004). Area under the receiver operating characteristics (AUROC) curves resulted in an AUC > 0.92 for all four antigen-cytokine pairs. Conclusion: The in vitro Mycobacterium tuberculosis-specific immune response in HIV-infected individuals that progress toward developing TB disease is different from those in HIV-infected individuals that do not progress to developing TB. These differences precede the clinical diagnosis of active TB up to 2 years, paving the way for the development of immune based diagnostics to predict TB disease at an early stage.

Biomarkers of cell-mediated immunity to bovine tuberculosis

Whole blood based assays, particularly interferon gamma (IFN-γ) release assays (IGRAs), are used for the diagnosis of both bovine and human tuberculosis (TB). The aim of the current study was to evaluate a panel of cytokines and chemokines for potential use as diagnostic readouts indicative of Mycobacterium bovis (M. bovis) infection in cattle. A gene expression assay was used to determine the kinetics of the response to M. bovis purified protein derivative and a fusion protein consisting of ESAT-6, CFP10, and Rv3615c upon aerosol infection with ∼10⁴ cfu of M. bovis. The panel of biomarkers included: IFN-γ, CXCL9, CXCL10, CCL2, CCL3, TNF-α, IL-1α, IL-1β, IL-1Ra, IL-22, IL-21 and IL-13. Protein levels of IFN-γ, CXCL9, and CXCL10 were determined by ELISA. Findings suggest that CXCL9, CXCL10, IL-21, IL-13, and several acute phase cytokines may be worth pursuing as diagnostic biomarkers of M. bovis infection in cattle.

Boosting effect of IL-7 in interferon gamma release assays to diagnose Mycobacterium tuberculosis infection

Background

A quarter of the world’s population is estimated to be infected with Myobacterium tuberculosis (Mtb). Infection is detected by immune response to M. tuberculosis antigens using either tuberculin skin test (TST) and interferon gamma release (IGRA’s), tests which have low sensitivity in immunocompromised. IL-7 is an important cytokine for T-cell function with potential to augment cytokine release in in-vitro assays. This study aimed to determine whether the addition of IL-7 in interferon-gamma release assays (IGRAs) improves its diagnostic performance of Mtb infection.

Methods

44 cases with confirmed TB and 45 household contacts without TB were recruited and 1ml of blood was stimulated in two separate IGRA’s tube set: one set of standard Quantiferon TB gold tubes mitogen, TB antigen and TB Nil; one set of customized Quantiferon TB gold tubes with added IL-7. Following IFN-γ and IP-10 release was determined using ELISA.

Results

We found that the addition of IL-7 led to significantly higher release of IFN-γ in individuals with active TB from 4.2IU/ml (IQR 1.4–6.9IU/ml) to 5.1IU/ml (IQR 1.5–8.1IU/ml, p = 0.0057), and we found an indication of a lower release of both IFN-γ and IP-10 in participants with negative tests.

Conclusions

In TB cases addition of IL-7 in IGRA tubes augments IFN-γ but not IP-10 release, and seems to lower the response in controls. Whether IL-7 boosted IGRA holds potential over standard IGRA needs to be confirmed in larger studies in high and low TB incidence countries.

Chemokines additional to IFN-γ can be used to differentiate among Mycobacterium tuberculosis infection possibilities and provide evidence of an early clearance phenotype

Current diagnostic tests for tuberculosis (TB) remain limited in their ability to discriminate between active TB (ATB) and latent TB infection (LTBI). Early clearance (EC) of TB by individuals exposed to Mycobacterium tuberculosis is a debated phenomenon for which evidence is lacking. We measured and compared secreted chemokines in the plasma fraction from 48 ATB, 38 LTBI, 162 presumed EC and 39 healthy controls (HC) using the QuantiFERON^®-TB Gold In-Tube assay. Single chemokine markers were limited in their ability to discriminate between ATB and LTBI: IFN-γ showed 16.7% sensitivity; CCL2 showed moderate sensitivity (70.8%) and specificity (74.4%); CXCL10 showed high sensitivity (87.5%) and specificity (78.9%). Compared to IFN-γ alone, IFN-γ combined with CXCL10 significantly improved (p < 0.001) the sensitivity and specificity to discriminate between ATB and HC (97.9% sensitivity and 94.9% specificity) and between ATB and LTBI (89.6% sensitivity and 71.1% specificity). Levels of CCL2 were very significantly lower (p < 0.0001) in EC compared to HC groups and hence CCL2 is a useful marker for EC. This study demonstrated the potential application of profiling using multiple chemokines for differentiating among the various M. tuberculosis infection possibilities. We also present evidence to support the EC phenomenon based on the decrease of CCL2 levels.

Increased TNF-α/IFN-γ/IL-2 and Decreased TNF-α/IFN-γ Production by Central Memory T Cells Are Associated with Protective Responses against Bovine Tuberculosis Following BCG Vaccination

Central memory T cell (Tcm) and polyfunctional CD4 T cell responses contribute to vaccine-elicited protection with both human and bovine tuberculosis (TB); however, their combined role in protective immunity to TB is unclear. To address this question, we evaluated polyfunctional cytokine responses by CD4 T cell effector/memory populations from bacille Calmette–Guerin (BCG) vaccinated and non-vaccinated calves by flow cytometry prior to and after aerosol challenge with virulent Mycobacterium bovis. Polyfunctional cytokine expression patterns in the response by Tcm, effector memory, and effector T cell subsets were similar between BCG-vaccinated and M. bovis-infected calves, only differing in magnitude (i.e., infected > vaccinated). BCG vaccination, however, did alter the kinetics of the ensuing response to virulent M. bovis infection. Early after challenge (3 weeks post-infection), non-vaccinates had greater antigen-specific interferon-γ (IFN-γ)/tumor necrosis factor-α (TNF-α) and lesser IFN-γ/TNF-α/IL-2 responses by Tcm cells than did vaccinated animals. Importantly, these differences were also associated with mycobacterial burden upon necropsy. Polyfunctional responses to ESAT-6:CFP10 (antigens not synthesized by BCG strains) were detected in memory subsets, as well as in effector cells, as early as 3 weeks after challenge. These findings suggest that cell fate divergence may occur early after antigen priming in the response to bovine TB and that memory and effector T cells may expand concurrently during the initial phase of the immune response. In summary, robust IFN-γ/TNF-α response by Tcm cells is associated with greater mycobacterial burden, while IFN-γ/TNF-α/IL-2 response by Tcm cells are indicative of a protective response to bovine TB.

Interleukin-17A as a Biomarker for Bovine Tuberculosis

T helper 17 (Th17)-associated cytokines are integral to the immune responses to tuberculosis, initiating both protective and harmful inflammatory responses. The aim of the present study was to evaluate applied aspects of interleukin-17 (IL-17) biology in the context of Mycobacterium bovis infection of cattle. Using transcriptome sequencing (RNA-Seq), numerous Th17-associated cytokine genes (including IL-17A, IL-17F, IL-22, IL-19, and IL-27) were upregulated >9-fold in response to purified protein derivative stimulation of peripheral blood mononuclear cells from experimentally M. bovis-infected cattle. Protective vaccines elicited IL-17A, IL-17F, IL-22, and IL-27 responses. Reduced IL-17A responses by vaccine recipients, compared to nonvaccinated animals, at 2.5 weeks after M. bovis challenge correlated with reduced disease burdens. Additionally, IL-17A and interferon gamma (IFN-γ) responses were highly correlated and exhibited similar diagnostic capacities. The present findings support the use of Th17-associated cytokines as biomarkers of infection and protection in the immune responses to bovine tuberculosis.

Application of Long-term cultured Interferon-γ Enzyme-linked Immunospot Assay for Assessing Effector and Memory T Cell Responses in Cattle

Effector and memory T cells are generated through developmental programing of naïve cells following antigen recognition. If the infection is controlled up to 95 % of the T cells generated during the expansion phase are eliminated (i.e., contraction phase) and memory T cells remain, sometimes for a lifetime. In humans, two functionally distinct subsets of memory T cells have been described based on the expression of lymph node homing receptors. Central memory T cells express C-C chemokine receptor 7 and CD45RO and are mainly located in T-cell areas of secondary lymphoid organs. Effector memory T cells express CD45RO, lack CCR7 and display receptors associated with lymphocyte homing to peripheral or inflamed tissues. Effector T cells do not express either CCR7 or CD45RO but upon encounter with antigen produce effector cytokines, such as interferon-γ. Interferon-γ release assays are used for the diagnosis of bovine and human tuberculosis and detect primarily effector and effector memory T cell responses. Central memory T cell responses by CD4(+) T cells to vaccination, on the other hand, may be used to predict vaccine efficacy, as demonstrated with simian immunodeficiency virus infection of non-human primates, tuberculosis in mice, and malaria in humans. Several studies with mice and humans as well as unpublished data on cattle, have demonstrated that interferon-γ ELISPOT assays measure central memory T cell responses. With this assay, peripheral blood mononuclear cells are cultured in decreasing concentration of antigen for 10 to 14 days (long-term culture), allowing effector responses to peak and wane; facilitating central memory T cells to differentiate and expand within the culture.

Thermostability of IFN-γ and IP-10 release assays for latent infection with Mycobacterium tuberculosis: A TBnet study

INTRODUCTION

Interferon-γ (IFN-γ) inducible protein 10kD (IP-10) and IFN-γ release assays (IGRAs) are immunodiagnostic tests aiming to identify the presence of specific cellular immune responses, interpreted as markers for latent infection with Mycobacterium tuberculosis. Incubation at higher temperatures could affect IFN-γ and IP-10 responsiveness in order to improve the performance of IP-10 release assays and IGRAs.

AIM

The aim of this study was to assess the robustness of whole blood based IP-10 release assay and IGRAs and the effect of hyper-thermic incubation (39 °C) on the diagnostic accuracy of IP-10 release assay and IGRAs.

RESULTS

We included 65 patients with confirmed pulmonary tuberculosis and 160 healthy controls from 6 European centres collaborating in the TBnet. In patients, IP-10 responses increased 1.07 (IQR 0.90-1.36) fold and IFN-γ responses decreased 0.88 (IQR 0.57-1.02) fold, with 39 °C compared to 37 °C incubation temperature. At 37 °C IGRA sensitivity was 85% and IP-10 sensitivity was 82%, whereas specificity was 97% for both tests (p > 0.8). These minor changes observed as a result of hyper-thermic incubation were not sufficient to impact IGRA and IP-10 release assay test performance.

CONCLUSION

The performance of IGRA and IP-10 release assays is robust despite variations in the incubation temperature between 37 °C and 39 °C.

The evaluation of candidate biomarkers of cell-mediated immunity for the diagnosis of Mycobacterium bovis infection in African buffaloes (Syncerus caffer)

We evaluated commercially available bovine enzyme linked immunosorbent assays (ELISA) and a human IP-10 ELISA to measure IP-10, MIG, MCP-1, MCP-2, MCP-3 and IL1-RA in buffalo plasma in order to identify sensitive markers of the immune response to Mycobacterium bovis-specific peptides. Additionally, we found that all coding mRNA sequences of these cytokines showed very high homology with their homologues in domestic cattle (97-99%) as did the derived amino acid sequences (97-99%). This high sequence homology between cattle and buffaloes supports the use of bovine ELISAs for the detection these cytokines in buffaloes. MCP-1 concentration showed a positive correlation with that of IFN-γ (p=0.0077) and appears to occur in far greater abundance in buffaloes when compared to humans. Using a bovine IP-10 ELISA, levels of this cytokine were found to be significantly increased in antigen-stimulated blood samples from M. bovis test positive buffaloes (p<0.0001) and IP-10 was detected in far greater abundance than IFN-γ. Measurement of IP-10 with this ELISA may prove to be a sensitive marker of M. bovis infection in African buffaloes.

Whole blood assay and visceral leishmaniasis: Challenges and promises

For years, the ability to study immune responses in patients with active visceral leishmaniasis (VL) has been hampered by the absence of detectable antigen-specific Th1 responses using cells from peripheral blood mononuclear cells (PBMCs). Employing whole blood assay (WBA), we recently reported that whole blood cells of active VL patients maintain the capacity to secrete significant levels of antigen driven IFN-γ and IL-10. Furthermore, WBA that uses soluble leishmania antigen (SLA) have advantages over the leishmanin skin test (LST), in terms of higher specificity and better correlation with surrogate markers of exposures to Leishmania donovani. These findings open the door to a series of immunological and epidemiological studies not previously possible for VL. In the present review, we discuss current status, future perspectives as well as obstacles in the research on WBA. Research in this area is essential for development of potential immunological and epidemiological tools for VL.

Effect of prolonged incubation time on results of the QuantiFERON TB gold in-tube assay for diagnosis of latent tuberculosis infection

Previous reports have shown that the sensitivity of the 6-day lymphocyte stimulation test is much higher than those of commercially available gamma interferon release assays (IGRAs). The aim of this study was to elucidate the effect of prolonged incubation on the results of the QuantiFERON TB Gold in-tube (QFT-GIT) assay. Patients aged >20 years with suspected tuberculosis (TB) were recruited prospectively from 1 May 2009 to 31 December 2010. In addition, healthy volunteers with no history of TB treatment were included as controls. For each participant, three sets of the QFT-GIT assay were performed using 24-, 48-, and 72-h incubation tests, and the results were compared. Thirty-seven patients with suspected pulmonary TB and 33 healthy controls were enrolled in the study. Of the 37 patients with suspected TB, the QFT-GIT assay results were positive for 28 (75.7%) after a 24-h incubation period. After prolonged incubation, the results differed in four (10.8%) of the 37 patients suspected of having TB. Among 27 patients with culture-confirmed TB, the sensitivities of the QFT-GIT assay after the 24-, 48-, and 72-h incubation tests were 85.2%, 81.5%, and 81.5%, respectively. Among the 33 healthy controls, the QFT-GIT assay results were positive in two (6.1%) after a 24-h incubation period. The results changed for two (6.1%) of the 33 healthy controls after prolonged incubation. The specificities of the QFT-GIT assay after 24, 48, and 72 h of incubation were 93.9%, 87.9%, and 90.9%, respectively. Prolonging the incubation time did not increase the sensitivity of the QFT-GIT assay. The manufacturer-recommended incubation time of 16 to 24 h should be respected because prolonged incubation can cause indeterminate or false-positive results.

A simple method to quantitate IP-10 in dried blood and plasma spots

BACKGROUND

Antigen specific release of IP-10 is an established marker for infection with M.tuberculosis. Compared to IFN-γ, IP-10 is released in 100-fold higher concentrations enabling the development of novel assays for detection. Dried blood spots are a convenient sample for high throughput newborn screening.

AIM

To develop a robust and sensitive ELISA-based assay for IP-10 detection in plasma, dried blood spots (DBS) and dried plasma spots (DPS); to validate the ELISA in clinically relevant samples; and to assess the performance of the assay for detection of Cytomegalovirus (CMV) and M.tuberculosis specific immune responses.

METHOD

We raised mice and rat monoclonal antibodies against human IP-10 and developed an ELISA. The assay was validated and applied to the detection of CMV and M.tuberculosis specific responses in 18 patients with immune reactivity towards M.tuberculosis and 32 healthy controls of which 22 had immune reactivity towards CMV and none towards M.tuberculosis. We compared the performance of this new assay to IFN-γ.

RESULTS

The ELISA was reliable for IP-10 detection in both plasma and filter paper samples. The linear range of the ELISA was 2.5-600 pg/ml. IFN-γ was not readily detectable in DPS samples. IP-10 was stabile in filter paper samples for at least 4 weeks at 37 °C. The correlation between IP-10 detected in plasma, DPS and DBS samples was excellent (r(2)>0.97).

CONCLUSIONS

This newly developed assay is reliable for IP-10 quantification in plasma, DBS and DPS samples from antigen stimulated and non-stimulated whole blood. The filter paper assays enable easy sample acquisition and transport at ambient temperature e.g. via the postal system. The system can potentially simplify diagnostic assays for M.tuberculosis and CMV infection.

IP-10 release assays in the diagnosis of tuberculosis infection: current status and future directions

The current state-of-the-art tests for infection with Mycobacterium tuberculosis - the IFN-γ release assays - rely on accurate measurement of the cytokine IFN-γ. Many other potential biomarkers are expressed in concert with IFN-γ, and IP-10 in particular has shown promising results. IP-10 is produced in large amounts, allowing for the development of new and simplified test platforms, such as lateral flow. In this review, we summarize the results of 22 clinical studies exploring the use of IP-10 as an alternative marker to IFN-γ. The studies report that diagnostic accuracy of IP-10 is on par with IFN-γ, but also that IP-10 may be more robust in young children and in HIV-infected individuals with low CD4 cell counts. We conclude the review by presenting limitations of the published works and outline recent developments and future directions.

Joint effects of febrile acute infection and an interferon-γ polymorphism on breast cancer risk

Background

There is an inverse relationship between febrile infection and the risk of malignancies. Interferon gamma (IFN-γ) plays an important role in fever induction and its expression increases with incubation at fever-range temperatures. Therefore, the genetic polymorphism of IFN-γ may modify the association of febrile infection with breast cancer risk.

Methodology and Principal Findings

Information on potential breast cancer risk factors, history of fever during the last 10 years, and blood specimens were collected from 839 incident breast cancer cases and 863 age-matched controls between October 2008 and June 2010 in Guangzhou, China. IFN-γ (rs2069705) was genotyped using a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry platform. Odds ratios (OR) and 95% confidence intervals (CIs) were calculated using multivariate logistic regression. We found that women who had experienced ≥1 fever per year had a decreased risk of breast cancer [ORs and 95% CI: 0.77 (0.61–0.99)] compared to those with less than one fever a year. This association only occurred in women with CT/TT genotypes [0.54 (0.37–0.77)] but not in those with the CC genotype [1.09 (0.77–1.55)]. The association of IFN-γ rs2069705 with the risk of breast cancer was not significant among all participants, while the CT/TT genotypes were significantly related to an elevated risk of breast cancer [1.32 (1.03–1.70)] among the women with <1 fever per year and to a reduced risk of breast cancer [0.63 (0.40–0.99)] among women with ≥1 fever per year compared to the CC genotype. A marked interaction between fever frequencies and the IFN-γ genotypes was observed (P for multiplicative and additive interactions were 0.005 and 0.058, respectively).

Conclusions

Our findings indicate a possible link between febrile acute infection and a decreased risk of breast cancer, and this association was modified by IFN-γ rs2069705.

Evaluation of gamma interferon (IFN-γ)-induced protein 10 responses for detection of cattle infected with Mycobacterium bovis: comparisons to IFN-γ responses

Gamma interferon (IFN-γ)-induced protein 10 (IP-10) has recently shown promise as a diagnostic biomarker of Mycobacterium tuberculosis infection of humans. The aim of the current study was to compare IP-10 and IFN-γ responses upon Mycobacterium bovis infection in cattle by using archived samples from two aerosol inoculation studies. In the first study (10(4) CFU M. bovis by aerosol, n = 7), M. bovis purified protein derivative (PPDb)-specific IP-10 and IFN-γ gene expression was detected as early as 29 days after challenge. PPDb-specific IP-10 and IFN-γ mRNA responses followed a similar pattern of expression over the course of this study and were highly correlated (r = 0.87). In the second study (10(5) CFU M. bovis by aerosol, n = 5), IP-10 and IFN-γ (protein) responses to mycobacterial antigens were compared following challenge. IFN-γ responses to mycobacterial antigens were detected at 29 days after challenge and were sustained during the remainder of the study. IFN-γ responses to mycobacterial antigens exceeded corresponding responses in nonstimulated cultures. IP-10 responses to mycobacterial antigens exceeded preinfection responses at 7, 29, and 63 days after challenge. In contrast to IFN-γ responses, IP-10 responses to mycobacterial antigens generally did not exceed the respective responses in nonstimulated cultures. IP-10 responses to medium alone and to mycobacterial antigens followed a similar pattern of response. Correlations between IP-10 and IFN-γ (protein) responses were modest (r ≈ 0.50 to 0.65). Taken together, these findings do not support the use of IP-10 protein as a biomarker for bovine tuberculosis using the current testing protocol and reagents; however, mRNA-based assays may be considered for further analysis.