For depression, a meta-analysis demonstrated that peripheral levels of interleukin-6 (IL-6), tumour necrosis factor (TNF)-alpha, IL-10, the soluble IL-2 receptor, C-C chemokine ligand 2, IL-13, IL-18, IL-12, the IL-1 receptor antagonist, and the soluble TNF receptor 2 were increased in patients suffering from major depression compared to controls. Here, IL18 is linked to major depressive disorder.