Consistent with a role for cytokines in depression, meta-analyses have established that circulating concentrations of the pro-inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-α were elevated in non-medicated depressed patients, whereas variations of IL-1β were less consistently demonstrated (Dowlati et al., 2010; Liu et al., 2012a), possibly because of the difficulty in detecting the very low levels of this interleukin in human circulation. This evidence concerns the gene TNF and depressive symptom measurement.