BDNF and major depressive disorder: Cumulative meta-analyses revealed that the levels of proteins involved in inflammatory regulation, such as interleukin-6 and C-reactive proteins, were higher in patients with major depression than in nondepressed controls [10,11], and some neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), were lower in the serum of a patient with depression than in healthy controls [12].