IL6 and major depressive disorder: Plasma IL-6 concentration was elevated in patients with MDD (1.46 pg/mL, IQR 0.80–4.0 pg/mL, n = 18) compared to healthy male volunteers (0.85 pg/mL, IQR 0.72–1.25 pg/mL, n = 13; P = 0.029, Fig. 1a).