MIGRAs: are they the new IGRAs? Development of monokine-amplified IFN-γ release assays

Use of IP-10 detection in dried plasma spots for latent tuberculosis infection diagnosis in contacts via mail

The aim of this study was to test the use of IP-10 detection in dried plasma from contact studies individuals (contacts of smear positive patients), by comparing it with IP-10 and IFN-γ detection in direct plasma, to establish IP-10 detection in DPS as a useful assay for LTBI diagnosis. Whole blood samples were collected from 80 subjects: 12 with active tuberculosis (TB), and 68 from contact studies. The amount of IFN-γ produced by sensitized T cells was determined in direct plasma by QuantiFERON Gold In-Tube test. IP-10 levels were determined in direct and dried plasma by an in-house ELISA. For dried plasma IP-10 determination, two 25 µl plasma drops were dried in Whatman903 filter paper and sent by mail to the laboratory. Regarding TB patients, 100.0%, 91.7% and 75.0% were positive for IFN-γ detection and IP-10 detection in direct and dried plasma, respectively. In contacts, 69.1%, 60.3% and 48.5% had positive results after IFN-γ and IP-10 in direct and dried plasma, respectively. The agreement among in vitro tests was substantial and IP-10 levels in direct and dried plasma were strongly correlated (r = 0.897). In conclusion, IP-10 detection in dried plasma is a simple and safe method that would help improve LTBI management.

Use of IFN-γ and IP-10 detection in the diagnosis of latent tuberculosis infection in patients with inflammatory rheumatic diseases

OBJECTIVES

Biologic agents are used against rheumatic diseases, however, they increase the risk of developing severe infections and diseases such as tuberculosis. We aimed to determine the benefits of IP-10 detection to diagnose latent tuberculosis infection (LTBI) in patients with inflammatory rheumatic diseases on different immunosuppressive drug regimens, and compare these results with IFN-γ detection.

MATERIALS AND METHODS

We included 64 patients with inflammatory rheumatic diseases. We used QuantiFERON Gold In-Tube (QFN-G-IT) and T-SPOT.TB to detect IFN-γ production, and an in-house ELISA for IP-10 detection from the previous QFN-G-IT stimulated samples. We assessed the combined use of IFN-γ release assays (IGRAs) and IP-10 test, and analyzed the influence of immunotherapy on the tests performance.

RESULTS

We obtained 34.9% positive results by T-SPOT.TB, 25.0% by QFN-G-IT and 31.3% by IP-10 test. The combined use of IGRAs and IP-10 detection increased significantly the amount of positive results (p < 0.0001). Treatment intake had no significant effect on in vitro tests (p > 0.05).

CONCLUSIONS

IP-10 and IFN-γ detection is comparable and their combined use could increase the number of positive results in the diagnosis of LTBI in rheumatic patients. The tested assays were not influenced by rheumatoid immunosuppressive therapy. Thus, IP-10 could be of use in the development of new and improved LTBI diagnostic tools.

T- and B-cell responses and previous exposure to hepatitis B virus in 'anti-HBc alone' patients

A serologic response to hepatitis B virus (HBV) defined as 'anti-HBc alone' is commonly observed, but its significance remains unclear. This study aimed to define the relationship between 'anti-HBc alone' serostatus and HBV infection, including HBV-specific T- and B-cell memory responses. We enrolled 31 'anti-HBc alone' patients. Total HBV DNA and cccDNA were tested by nested polymerase chain reaction (PCR) analysis in liver samples from 22 'anti-HBc alone' patients vs controls (chronic or resolved HBV infection), followed by HBsAg/HBcAg immunohistochemical (IHC) staining. IFN-γ secretion by HBV-specific T cells was compared in individuals who were 'anti-HBc alone' (n = 27), resolved HBV (n = 21), chronic HBV (n = 24) and 12 healthy controls using enzyme-linked immunospot (ELISpot) assays. An HBsAg-IgG B-cell ELISpot assay was performed in 'anti-HBc alone' patients before and after one dose of recombinant HBsAg vaccine. The majority (23/31, 74.2%) of the 'anti-HBc alone' individuals were co-infected with HCV. Infrequent intrahepatic total HBV DNA (2/22, 9.1%) and cccDNA (1/22, 4.5%) were detected in biopsies; HBsAg and HBcAg IHC staining was negative. HBV-specific T-cell responses were similar between 'anti-HBc alone' individuals and HBV resolvers. Circulating HBV-memory B-cell responses were detected in all 'anti-HBc alone' individuals, consistent with an HBsAg-specific memory pool. After one HBV vaccine dose, increased anti-HBs antibody levels were observed, accompanied by an expansion of HBsAg-specific memory B cells (P = 0.0226). 'Anti-HBc alone' individuals showed HBV-specific T-cell and memory B-cell responses typical of previous viral exposure and protective memory, suggesting a resolved infection.

Dried plasma spots in the diagnosis of tuberculosis: IP-10 release assay on filter paper

Interferon (IFN)-γ release assays (IGRAs) are probably the most accurate tests for the detection of latent Mycobacterium tuberculosis infection, but IGRAs are labour intensive and the transport of samples over longer distances is difficult. IFN-γ-induced protein (IP)-10 is expressed at 100-fold higher levels than IFN-γ, and IP-10 release assays have comparable performance to IGRAs. The aim of this study was to explore the diagnostic potential of a novel IP-10 release assay based on dried plasma spots (DPS). The presence of IP-10 and IFN-γ was determined in plasma and in DPS by ELISA. Diagnostic algorithms for plasma and DPS tests for IP-10 were developed on a training cohort comprising 60 tuberculosis (TB) patients and 59 healthy controls. Diagnostic accuracy was assessed in a validation cohort comprising 78 TB patients and 98 healthy controls. Plasma was measured in Spain and DPS samples were sent to Denmark using the conventional postal service for analysis. IP-10 was readily detectable in both plasma and DPS, and correlation was excellent (r(2) = 0.95). QuantiFERON-TB Gold In-Tube (QFT-TB) and IP-10 in DPS and plasma rendered comparable sensitivity (78%, 82% and 84%, respectively), specificity (100%, 97% and 97%, respectively) and indeterminate rates (p>0.55). The DPS-based IP-10 test has comparable diagnostic accuracy to the QFT-TB and samples can be sent via conventional mail over long distances for analysis without affecting the results.

Recent advances in the diagnosis of Mycobacterium tuberculosis

Molecular technologies offer the greatest potential for laboratories in resource-rich countries because they have the highest sensitivity and specificity. Continued use of new technologies will be crucial in elucidating the true epidemiology and pathogenesis of a disease, including the less well studied diseases. Continued development of affordable, sensitive, and specific diagnostic tools will be required for use in resource-poor settings, where the incidence of disease is highest.

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.