BDNF and major depressive disorder: 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).