TNF and major depressive disorder: For example, a recent meta-analysis evidenced that individuals with depression exhibit elevated peripheral levels interleukin (IL)-6, tumor necrosis factor (TNF)- α, IL-10, the soluble IL-2 receptor, C-C chemokine ligand 2, IL-13, IL-18, IL-12, the IL-1 receptor antagonist, and the soluble TNF receptor 2 compared to healthy controls (7).