CXCL8 and major depressive disorder: A number of pro-inflammatory markers, including tissue necrosis factor alpha (TNF-α), C-reactive protein (CRP), interleukin-6 (IL-6), and interleukin-8 (IL-8) of both blood and cerebrospinal fluid, were elevated in mental disorders such as depression, schizophrenia and anxiety [10]; multiple factors including psychological influences, both genetic and biological, were also involved in the initiation of depressive episodes [11].