IL4 and major depressive disorder: Adolescents with depression exhibited significantly higher serum levels of IL-4, IFN-γ, and TNF-α compared with healthy controls (IL-4: 14.71 ± 6.83 vs. 11.73 ± 10.90 pg/mL, t = 2.859, p = 0.006; IFN-γ: 18.34 ± 21.75 vs. 9.60 ± 10.13 pg/mL, t = 2.058, p = 0.042; TNF-α: 8.41 ± 4.17 vs. 6.92 ± 4.54, t = 2.324, p = 0.018) (Figures 2A–C).