IL6 and major depressive disorder: A meta-analysis of 107 studies in the general adult population found that individuals with depression had elevated C-reactive protein (CRP), interleukin (IL)-3, IL-6, IL-12, IL-18, soluble interleukin 2 receptor (sIL-2R), and tumor necrosis factor alpha (TNF-α) levels with medium-effect sizes (Osimo et al., 2020).