IL18 and major depressive disorder: Studies have demonstrated that patients with MDD (major depressive disorder) exhibit increased peripheral blood inflammatory biomarkers, such as IL-6, TNF-α, IL-10, C-C motive chemokine ligand 2(CCL2), IL-13, IL-18, IL-12, and CRP (Liu et al. 2020b; Köhler et al. 2017; Perry et al. 2021; Felger et al. 2020).