Previous studies documented that patients with depression had elevated levels of pro-inflammatory markers, such as C-reactive protein (CRP), interleukin-6 (IL-6) and tumour necrosis factor alpha (TNF-α), which were also manifested in the cytokine profiles of patients with organ-specific and/or systemic autoimmunity [8, 9, 32–35]. Here, TNF is linked to major depressive disorder.