IL18 and major depressive disorder: A recent meta‐analysis comprising 3212 MDD participants and 2798 healthy controls has shown that IL‐6, TNF‐α, soluble IL‐12 receptor, CCL2, IL‐13, IL‐18, IL‐12 and the soluble TNF receptor 2 are elevated in MDD individuals compared to healthy controls, whereas IFN‐γ levels are reduced (Köhler, Freitas, Maes, Andrade & Liu, 2017).