For example, almost all patients experience acute sickness, including symptoms of fatigue, malaise, myalgia, arthralgia, anorexia, apathy and cognitive impairment.11, 12, 13 IFN-α administration to humans replicates multiple pathologies central to depression, thereby providing support for the notion that endogenous cytokines that mediate innate immune responses can contribute to the state of depression.14 This evidence concerns the gene IFNA1 and major depressive disorder.