In keeping with the view that increased pro-inflammatory cytokine activity might promote depression through their effects on growth factors, serum BDNF reductions during the course of IFN-α treatment were inversely correlated with depressive scores (Kenis et al., 2011), although it has also been found that depression severity during IFN-α immunotherapy was associated with lower BDNF levels prior to treatment, but not with the BDNF reductions that occurred during treatment (Lotrich et al., 2013). Here, BDNF is linked to depressive symptom measurement.