“…IDO can be studied quantitatively by measuring mRNA expression or protein levels or enzymatic activity (product-to-substrate ratio; Li et al, 2011; Mehra et al, 2012; Suzuki et al, 2012, 2013; Huang et al, 2013; Bipath et al, 2015; Zhang et al, 2019). IDO activity can be detected in host fluids including blood, sputum, pleural fluid, cerebrospinal fluid and urine (Almeida et al, 2009; Li et al, 2011; Suzuki et al, 2012, 2013; Bipath et al, 2015; Adu-Gyamfi et al, 2017; Gautam et al, 2018; Yarbrough et al, 2018). IDO mRNA expression has been studied using rt-PCR, and IDO protein has been measured by western blot, radioimmunoassay and immunofluorescence methods (Almeida et al, 2009; Soliman et al, 2013; Zhang et al, 2019).…”