KEAP1 and depressive symptom measurement: In the review, the author would like to discuss the role of Keap1 [Kelch-like erythroid cell-derived protein with CNC homology [ECH]-associated protein 1)]-Nrf2 [Nuclear factor (erythroid 2-derived)-like 2] system in the pathophysiology of depression since Keap1-Nrf2 system plays a key role in inflammation.