Serum samples were collected from a randomized, placebo-controlled 12-week clinical trial of minocycline (200 mg/day, added as usual to treatment) in adults experiencing MDD to determine changes in interleukin-6 (IL-6), lipopolysaccharide binding protein (LBP) and brain-derived neurotrophic factor (BDNF). Here, BDNF is linked to major depressive disorder.