Innate immune gene expression is known to alter behavior. The most serious side effect of treatment of cancer patients with proinflammatory interferon and interleukin is severe depression that must be treated with antidepressants. Multiple other studies have linked negative affect and depression to innate immune activation (Kelley 2011). Bacterial endotoxin (LPS) an effective inducer of innate immune genes causes sickness behavior and negative affect across multiple species. In rodents, models of depression-like behavior are linked to innate immune activation and in healthy humans LPS infusions reduce reward responses and increase depressed mood (Eisenberger et al. 2010). Increased negative affect is an important component of the neurobiology of addiction (Koob and Volkow 2010).
