TNF and major depressive disorder: Furthermore, IL-6, tumor necrosis factor-alpha (TNF-α), and IL-1β are implicated in the pathophysiology of depression (Brebner et al., 2000), and individuals with depression often have elevated circulating IL-1β, IL-6, and TNF with reduced levels of interferon-gamma (IFN-γ), IL-10, and IL-4 (Goldsmith et al., 2016).