BDNF and major depressive disorder: Previous studies have shown that increased levels of proinflammatory cytokines are seen in depressed patients.16 Also, there is a linear relationship between severity of depression and concentration of inflammatory cytokines, including IL-1β, IL-8, TNF-α,17 and IL-6.18 BDNF levels in women with PPD are low.19 A marked decrease in serum BDNF concentration occurs both before and after delivery.20 Antidepressant treatments increase neural plasticity by activating BDNF.21 Yoshimura et al indicated a negative correlation between serum BDNF levels and baseline HDRS scores.