BDNF and depressive disorder: The correlation analysis showed that before treatment, the IL-18 and IL-1β levels were positively correlative with the BDI scores (r = 0.781, r = 0.2583, P < 0.001, P = 0.012), and the BDNF level was negatively correlative with the BDI scores (r = −0.3277, P = 0.001) in the depression group (see Figure 2).