BDNF and major depressive disorder: What is more, NLR, monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial cellline-derived neurotrophic factor (GDNF), interleukin (IL), soluble tumor necrosis factor receptor I (sTNFr1), and soluble tumor necrosis factor receptor II (sTNFr2) have been found to be associated with MDD [12, 13] as compared with healthy controls [14].