[15,17,18] Increased levels of C-reactive protein ([CRP]; ≥1.0 mg/L), interleukin-6, interleukin-1, and tumor necrosis factor-α (TNF-α) have been repeatedly shown in clinical trials and meta-analyses to have a positive correlation with MDD [15,17,19,20,21,22]. Here, IL6 is linked to major depressive disorder.