We mention this fact because it indicates that the variation in plasma concentrations of both 5-HT and kynurenine, variation that was associated with SSRI response and severity of MDD symptoms (see Figure 4), respectively, appeared to be associated with the effects of proteins, TSPAN5, ERICH3, DEFB1 and AHR, which had not previously figured prominently--or at all--in our thinking with regard to MDD pathophysiologic mechanism(s). Here, DEFB1 is linked to major depressive disorder.