IL6 and major depressive disorder: Persistent sub-clinical inflammation is one of the underlying factors that contribute to the pathophysiology of chronic diseases (e.g., cardiovascular disease, type 2 diabetes, depression, and obesity) [1,2] and is characterised by changes in biological markers: an increased concentration of proinflammatory molecules (e.g., C-reactive protein (CRP), interleukin-6 (IL-6), and tumour necrosis factor-α (TNF-α)) and a reduced concentration of anti-inflammatory molecules (e.g., adiponectin) in circulation.