Interestingly, immune-cell derived BDNF is considered to have a protective role in neuroimmunological disorders such as multiple sclerosis and CNS injury,95, 99, 102 and this notion has been extended to psychiatric disorders.103 Indeed, clinical data indicate that leukocyte BDNF gene expression is decreased in MDD patients,104, 105 whereas serum BDNF restoration and clinical improvement in these patients are paralleled by increases in leukocyte BDNF expression following antidepressant treatment.106, 107. Here, BDNF is linked to major depressive disorder.