For example, the anti-inflammatory cytokine IL-2 is altered in people with schizophrenia [63,84,85]; IL-6 concentrations are associated with depression [42,45,86]; elevated levels of IL-6 are trait markers for BD [87] and schizophrenia [63,88]; elevations of IL-8 in cerebrospinal fluid are seen in patients with schizophrenia [89]; IL-18 is increased in patients with depression [50,61]; the level of TNF-α increased in patients with SCZ, MDD [63] and BD [90]. Here, TNF is linked to major depressive disorder.