Anhedonic MDD showed increased serum levels of IL-2 (0.36 ± 0.14 pg/ml vs. 0.09 ± 0.04 pg/ml, t = 2.025, P = 0.047), IL-6 (4.12 ± 0.75 pg/ml vs. 1.46 ± 0.19 pg/ml, t = 3.803, P < 0.001), and CRP (2.25 ± 0.64 mg/l vs. 0.85 ± 0.05 mg/l, t = 2.476, P = 0.016) compared with nonanhedonic MDD (Figures 1D,E). Here, IL2 is linked to major depressive disorder.