TNF and major depressive disorder: In animal experiments, peripherally administered proinflammatory cytokines IL-1β and TNF-α as well as lipopolysaccharide (LPS) and synthetic compound mimicking viral infection (Poly (I:C)) have induced ‘sickness behaviour’ characterized by lethargy, depression, anxiety, loss of appetite, and sleepiness (Dantzer, 2001, Gibney et al., 2013).