IFNG and major depressive disorder: In addition, to identify whether these behavioral effects were accompanied by changes in the circulating cytokine levels and central monoamine activity within several stressor-sensitive brain regions that have been implicated in depression and anxiety, the serum levels of the pro-inflammatory cytokines (IL-6 and TNF-á), Th1 cytokine (IL-2 and IFN-γ), Th2 inflammatory cytokine (IL-4) and Th17 cytokine (IL-17A) and monoamine (DA and 5-HT) within the prefrontal cortex and hippocampus were measured during the development of behavioral responses-related depression.