TNF and major depressive disorder: For instance, numerous studies have reported that pro-inflammatory cytokines, most notably interleukin-1-beta (IL-1β), IL-6, interferon-alpha (IFN-α), and tumor necrosis factor-alpha (TNF-α), are altered in major depression and stressor-based animal models (Dowlati et al., 2010; Liu et al., 2012; Dahl et al., 2014).