TNF and major depressive disorder: Mrugacz et al.29 explored the correlation between inflammatory cytokine levels in tears and depression among 32 (14 male, 18 female) DED patients with an average age of 44.21 years; and observed that patients with depression had significantly higher inflammatory cytokine (IL-6, IL-17, and TNF-α) levels in tears than control participants, which reflects the severity of local immunological changes.