IL15 and major depressive disorder: Plasma concentrations of IL-1β, IL-1Ra, IL-5, IL-6, IL-7, IL-8, IL-10, G-CSF, IFN- γ, and TNF-α are significantly elevated in patients with MDD compared to healthy controls. IL-2, IL-15, and MIP-1α did not show significant differences in plasma concentrations between the two groups.