Almost one-half of non-depressed hepatitis C and cancer patients treated with interferon develop depressive symptoms associated with increased serum IL-6 levels (one of the more reliable peripheral biomarkers in major depression) (Loftis and Hauser, 2004), while significantly higher circulating concentrations of TNF-α and IL-6 were reported in depressed subjects compared with controls (Dowlati et al., 2010). Here, IL6 is linked to major depressive disorder.