IL6 and major depressive disorder: Examples of such immunologically important cytokines measured in the serum of patients with depression are IL-1, IL-2, IL-4, IL-5, IL-6, IL-10, IL-12, IL-13, IL-17, IFN-α, IFN-γ, TNF-α, and transforming growth factor (TGF)-β (2, 33, 61–64).