TNF and major depressive disorder: Research has shown that the concentrations of inflammatory biomarkers—including soluble interleukin-2 receptor (sIL-2R), tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, IL-12, and IL-18—are significantly higher in the bloodstream of individuals with depression than in those without, underscoring the critical role of inflammatory processes in this condition (5).