Potential role for IL-2 ELISpot in differentiating recent and remote infection in tuberculosis contact tracing.

Benjamin Krummel,Volker Schoellhorn,Heidrun Rath,Robert Hoerster,Christoph Lange,Alan Strassburg,Barbara Eker,Andrea Glaewe,Martin Ernst,Giovanni Sotgiu,Norbert Reiling,Waltraud Wappler,Ben Marais

doi:10.1371/journal.pone.0011670

Abstract

Interferon (IFN)-γ release assays (IGRA) have improved tuberculosis contact tracing, but discrimination of recent from remote Mycobacterium tuberculosis contacts is not possible by IGRA alone. We present results of a tuberculosis contact investigation with a new early-secretory-antigenic-target (ESAT)-6 and culture-filtrate-protein (CFP)-10 specific interleukin (IL)-2 ELISpot in addition to ESAT-6 and CFP-10 specific IFN-γ ELISpot and tuberculin skin testing (TST). Results of the TST, IFN-γ ELISpot and IL-2 ELISpot were positive in 6/172 (3.4%), 7/167 (4.2%) and 6/196 (3.1%) of contacts, respectively. Close contact (≥100 hours) to the index case increased the risk of positive results in the IFN-γ ELISpot, TST, and IL-2 ELISpot by 40.8, 19.3, and 2.5 times, respectively. Individuals with a positive IFN-γ ELISpot/negative IL-2 ELISpot result had a median (IQR) duration of index case exposure of 568 hours (133_1000) compared to individuals with a positive IFN-γ ELISpot/positive IL-2 ELISpot result (median = 24 hours; 20_130; p-value = 0.047). Combination of a M. tuberculosis specific IFN-γ ELISpot with a M. tuberculosis specific IL-2 ELISpot significantly improved the identification of individuals with the highest risk of recent M. tuberculosis infection and is a promising method that should be explored to target tuberculosis preventive chemotherapy.

Highlights

Identification and treatment of individuals with lasting Mycobacterium tuberculosis specific immune responses following recent contact to a contagious index case with pulmonary tuberculosis are crucial to tuberculosis control [1]
The diagnosis and management of LTBI has evolved over the last decade with improvements in the immunodiagnosis by M. tuberculosis specific interferon-c release assays (IGRA) in addition to the tuberculin skin test [2]
IGRA detect interferon-c release by mononuclear cells in the ELISpot (T-SPOT.TB – Oxford Immunotec, Abingdon, UK) or in whole blood in the ELISA (QuantiFERON-TB GOLD in tube; QFT-G-IT; Cellestis, Carnegie, Australia) following ex vivo contact with antigens that are naturally encoded in the M. tuberculosis genomic region of difference (RD)-1 and RD11

Summary

Introduction

Identification and treatment of individuals with lasting Mycobacterium tuberculosis specific immune responses (latent tuberculosis infection -, LTBI) following recent contact to a contagious index case with pulmonary tuberculosis are crucial to tuberculosis control [1]. IGRA detect interferon-c release by mononuclear cells in the ELISpot (T-SPOT.TB – Oxford Immunotec, Abingdon, UK) or in whole blood in the ELISA (QuantiFERON-TB GOLD in tube; QFT-G-IT; Cellestis, Carnegie, Australia) following ex vivo contact with antigens that are naturally encoded in the M. tuberculosis genomic region of difference (RD)-1 and RD11 (only QFT-G-IT). Long-lived central memory T-cells may persist even after successful treatment of tuberculosis [6,7] and are less likely to release IFN-c after short incubation with antigen while they are more likely to produce IL-2 upon antigen exposure than effector cells [7]. Assaying M. tuberculosis-specific T cell function defined solely by the quantification of IFN-c secretion after short term ex vivo incubation with M. tuberculosis-specific antigen may prove to be an insufficient indicator for recent inhalation exposure to M. tuberculosis. Simultaneous measures of other T cell function, such as M. tuberculosis-specific stimulation of IL-2 secretion may improve the discrimination of active versus remote LTBI [7]

Methods

Results

Discussion

Conclusion