MDD is also characterized by neurophysiological abnormalities of striatal, cortical midline, and limbic brain structures that regulate hormonal, autonomic, and emotional responses to reward and stress (4-6). Yet, it remains unclear how immune function relates to these depression-associated functional neuroimaging abnormalities. Studies of healthy volunteers (HCs) administered endotoxin or the typhoid vaccine have reported inflammation-associated increases in negative affect along with neurophysiological changes in brain regions comprising the affective and reward circuitry (7-8). However, because these studies were limited to HCs, it is possible that the observed inflammation-induced neurophysiological changes were adaptive and therefore not applicable to MDD populations. That is, it remains unclear whether any experimentally-induced immune abnormalities in MDD are correlated and therefore potentially causally-related to the neuroimaging abnormalities observed in MDD.