In patients with major depression or in animal models of stress-induced depression, levels of pro-inflammatory cytokines in the blood, such as interleukin IL-1b, IL-6, IL-18, IL-1Ra, tumor necrosis factor-α (TNF-α), and inflammasome components in immune cells, such as NLRP3, are significantly upregulated [38,90,113]. Here, IL18 is linked to major depressive disorder.