Further post-hoc comparisons found the significant differences in serum IL-8 levels in drug-free MDD patients versus HCs (F = 17.68, p < 0.001), MDD patients with SSRIs versus HCs (F = 4.79, p = 0.03), and drug-free MDD patients versus MDD patients with SSRIs (F = 24.00, p < 0.001) using Fisher’s LSD procedure in Figure 1B. This evidence concerns the gene CXCL8 and major depressive disorder.