Is IP-10 a Better Biomarker for Active and Latent Tuberculosis in Children than IFNc? Elizabeth Whittaker1*, Andrea Gordon 2 , Beate Kampmann1,2 1 Department of Paediatrics, Imperial College London, London, United Kingdom, 2 Wellcome Centre for Clinical Tropical Medicine, Imperial College London, London, United Kingdom Abstract Background: The blood based interferon-gamma release assays (IGRA) for the diagnosis of tuberculosis do not discriminate between active TB disease and latent TB infection (LTBI). The search for distinguishing biomarkers therefore continues, as the accurate diagnosis of tuberculosis is particularly challenging in children. IFN-c-inducible protein 10 (IP-10/CXCL10) has recently been evaluated as a marker for active TB in adults with promising results. Aim: To investigate this new biomarker for active TB and LTBI in paediatrics. Method: We measured IP-10 levels using ELISA in supernatants of whole blood samples stimulated with TB-specific- antigens and negative control antigen. Results: IP-10 is produced in high levels following mycobacterial antigen stimulation in active TB (n = 17) and LTBI (n = 16) compared to controls (n = 16) and to IFN-c. The baseline levels of IP-10 are increased in active TB and in LTBI, but there is no significant difference of stimulated levels of IP-10 between active TB and LTBI. Conclusions: IP-10 is a biomarker for tuberculosis in children. However like IFNc, IP-10 also does not distinguish between active TB and LTBI. Citation: Whittaker E, Gordon A, Kampmann B (2008) Is IP-10 a Better Biomarker for Active and Latent Tuberculosis in Children than IFNc?. PLoS ONE 3(12): e3901. doi:10.1371/journal.pone.0003901 Editor: Rosemary Jeanne Redfield, University of British Columbia, Canada Received August 11, 2008; Accepted November 4, 2008; Published December 9, 2008 Copyright: 2008 Whittaker et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was facilitated by consumable grants from the Peel Foundation and the European Society for Paediatric Infectious Diseases (ESPID). BK is funded by the Wellcome Trust (GR 077273). LW and BK are supported by the Biomedical Research Centre at Imperial College. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: e.whittaker@imperial.ac.uk Introduction The diagnosis of tuberculosis (TB) in the paediatric population remains a challenge, as TB can present similarly to many common childhood infections and shares many symptoms with HIV. Diagnosis is often based on contact history, clinical picture, tuberculin skin test (TST) responses and investigations including chest x-ray (CXR) rather than on the microbiological ‘‘gold standard’’ [1]. The paucibacillary nature of TB in childhood limits the microbiological yield and immunodiagnostic methods such as the Mantoux test have been widely used in paediatrics for many years[2]. In recent years new immunodiagnostic tests for tuberculosis have been developed: the commercially available Quantiferon TB Gold In Tube (Cellestis, Carnegie, Australia) and T-SPOT TB (Oxford Immunotec, Abingdon, UK) ELISPOT assays both measure interferon gamma (IFN-c) release by sensitized T cells after stimulation with peptides of M. tuberculosis specific antigens - Early Secretory Antigenic Target (ESAT)-6, Culture Filtrate Protein (CFP)-10 plus TB7.7 in the Quantiferon system.[3] These interferon gamma release assays (IGRA) are less influenced than the TST by factors frequently associated with childhood tuberculosis in developing countries, such as malnutri- tion and HIV co-infection [4]. BCG vaccine and environmental mycobacterial exposure are also known to influence TST results but not IGRA[5,6]. However, the IGRA poorly distinguish between active TB and latent TB infection (LTBI) and more recent studies question the sensitivity of these assays, particularly in some groups including younger children and immunocompro- mised patients. [7,8,9]. Recent studies looking at alternative markers for diagnosis of TB have identified a promising chemokine called IFN-c- inducible protein 10 (IP-10) [10]. Also known as CXCL10, it is a member of the CXC-chemokine family. Chemokines are a class of cytokines with chemotactic properties; they have a role in mediating leukocyte migration and activation. IP-10 is expressed in both lymphocytes and monocytes and is involved in trafficking of Th1 lymphocytes to areas of inflammation where it binds to CXCR3 (a receptor shared by IP-10, Mig and I-TAC)[11]. CXCR3 mRNA is expressed in T cells alone and thus IP-10 differs from other chemokines as it targets lymphocytes specifically and has no activity on neutrophils. In adult studies, high levels of IP-10 have been found in delayed type hypersensitivity reaction to Tuberculin Purified Protein Derivative (PPD)[12], in vivo in lymph node and lung tuberculous granulomas[13], in pleural effusions and plasma of TB infected patients[14,15] and plasma of TB-HIV co-infected patients diagnosed with immune reconstitution syndrome PLoS ONE | www.plosone.org 1 December 2008 | Volume 3 | Issue 12 | e3901