Major depressive disorder (MDD) patients (n = 30) exhibited higher levels of Nrf2 and its regulator Keap1, as well as NF-κB in the cytoplasm of peripheral blood mononuclear cells compared to healthy controls (n = 35), suggesting that depression may be characterized by up-regulation of the transcription factor Keap1-Nrf2 (Lukic et al., 2014). Here, KEAP1 is linked to depressive symptom measurement.