In patients with depression (Dowlati et al., 2010, Goldsmith et al., 2016, Haapakoski et al., 2015, Howren et al., 2009) and psychosis (Miller et al., 2011, Miller et al., 2013, Potvin et al., 2008, Upthegrove et al., 2014) who are acutely unwell, concentrations of IL-6 and other inflammatory markers are elevated compared with controls, which tend to normalize after recovery but continue to be elevated in treatment resistant patients (Goldsmith et al., 2016, Maes et al., 1997, O'Brien et al., 2007). Here, IL6 is linked to depressive symptom measurement.