IL6 and major depressive disorder: In MDD, prolonged activation of immune system [29–31] was identified with increased pro-inflammatory markers such as cytokines (interleukin (IL)-1, IL-2, IL-6, IL-8, IL-12, interferon (IFN)-γ, tumour necrosis factor (TNF)α) and adhesion molecules (intercellular molecule (ICAM)-1), while anti-inflammatory markers (e.g., IL-10) were reduced [32–34].