Our results showed that the plasma MLT concentration was decreased in T2DM patients with a higher level of HbA1c, and the plasma MLT levels were negatively correlated with not only the BRIEF-A cognitive score and CES-D depression score but also the inflammatory markers such as plasma concentrations of IL-6, CRP, sTREM1, and sTREM2. This evidence concerns the gene IL6 and major depressive disorder.