Exploring the human host response to
Exploring the human host response to TB provides opportunity for the discovery of biomarkers, and the development of additional diagnostics that do not require samples from the site of disease and that are not based on the detection of Mtb. Mass spectrometry (MS) allows rapid quantitative assessment of various analytes in clinical laboratories, and portable MS technology is becoming more available (Wiley et al., 2013; Hendricks et al., 2014; Creamer et al., 2014). Furthermore, the technological mct2 inhibitor exists to develop and deploy multi-analyte tests using multiple reaction monitoring MS (MRM-MS) (Hunter and Paramithiotis, 2010), and immunoassays for the detection and quantification of specific proteins can be easily developed for settings where fewer resources are available. Tests based on host protein panels have already demonstrated diagnostic capability and prediction of disease severity in conditions such as dengue fever and ovarian, endometrial and lung cancers (Farias-Eisner et al., 2010; Li et al., 2013; Nosov et al., 2009; Oikonomopoulou et al., 2008; Villar-Centeno et al., 2008). The overall objective of this study was the identification of protein expression patterns that are associated with TB but not with Mtb uninfected states, LTBI, or respiratory diseases other than TB (ORD). Such biomarkers might ultimately also be able to serve as surrogates for antituberculous treatment response. In this study we focussed on subjects living in the US as these are often diagnosed at earlier disease stages than individuals living in more resource-limited settings (Achkar et al., 2010), such as many regions in Sub-Saharan Africa and Asia, where mycobacterial cultures are not always available and TB is typically not diagnosed until it is sputum smear-positive and highly transmissible (Reid and Shah, 2009; Steingart et al., 2007). Due to the known impact of HIV co-infection on the pathogenesis and clinical presentation of TB (reviewed in (Achkar and Jenny-Avital, 2011)), we hypothesized that the host response in TB will differ according to HIV status. In this work we show that TB leads to changes in blood protein expression, and demonstrate that modestly sized panels of protein biomarkers that differed according to HIV status were able to accurately distinguish TB from LTBI, and ORD.
Discussion Our data demonstrate that the physiological changes associated with TB, including the effects of HIV co-infection, are reflected by the human host protein patterns in blood. Small panels of proteins could accurately distinguish TB from LTBI and ORD in HIV− and HIV+ individuals. Particularly relevant for clinical practice was that our biomarker signature was detectable in both smear-positive and smear-negative TB, including culture-negative TB, indicating a high sensitivity for early as well as more advanced TB. Furthermore, the high specificity was estimated based on TB suspects ultimately diagnosed with an ORD, the clinically relevant comparator group. In addition, following the expression levels of host proteins during antituberculous therapy might allow rapid assessment of the treatment response, and offer advantages over the currently used culture method. Although these results require validation in larger studies, our data hold promise that the detection of host protein changes could provide the basis for adjunctive rapid TB diagnostics, either by immunoassay or by using portable MS devices that are becoming more available (Wiley et al., 2013; Hendricks et al., 2014; Creamer et al., 2014). The panel proteins were derived from the most prominently observed TB related host processes — the immune response, tissue repair, and lipid metabolism. As combinations of antituberculous and host-modulating therapies hold promise to improve bacterial clearance (Gonzalez-Juarrero, 2012; Maiga et al., 2012; Martins, 2011), the host protein changes described in this work could also offer insights into which host/pathogen combination therapies may be promising. Soluble CD14 (sCD14) and SEPP1 were present in the TB panels for HIV+ and HIV− subjects. CD14 is a marker of pulmonary inflammation (Anas et al., 2010). Consistent with our findings, membrane and soluble CD14 become up regulated in TB (Druszczynska et al., 2013; Lawn et al., 2000; Hoheisel et al., 1995). Other infections or respiratory diseases also induce elevated sCD14, albeit usually at lower levels than TB (Hoheisel et al., 1995; Lawn et al., 2000), also consistent with our observations. SEPP1, which was down regulated in TB, is involved in selenium transport and homeostasis. SEPP1 deficient mice experience greater morbidity and mortality in Trypanosoma infection (Burk and Hill, 2009), apparently due to increased tissue injury associated with enhanced production of reactive oxygen species (Bosschaerts et al., 2008).