TNF and major depressive disorder: In addition to these measures in saliva, peripheral blood concentrations of inflammatory biomarkers, such as interleukin-1 beta (IL-1β), tumor necrosis factor alpha (TNF-α), and interleukin-6 (IL-6), have previously been found to be elevated in cases of MCI and depression in comparison to healthy age-matched controls (23, 24, 29).