A recent meta-analysis of 82 studies showed that levels of the cytokines Interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), IL-10, the soluble IL-2 receptor, C–C motif chemokine ligand 2 (CCL2), IL-13, IL-18, IL-12, the IL-1 receptor antagonist, and the soluble TNF receptor 2 were elevated in patients with depression compared to healthy control subjects, whereas interferon gamma (IFN-γ) levels were lower in depression (Köhler et al., 2017). Here, IL18 is linked to depressive disorder.