Post-mortem brain tissue from AD cases with depression (n = 23) and AD cases with no history of psychiatric illness (n = 25) were analyzed for a range of inflammatory markers, including markers of microglial function (Iba1, P2RY12, CD64 and CD68 measured by immunohistochemistry); endothelial inflammatory markers (ICAM-1 and VCAM-1 measured by ELISA); and cytokine levels (IFN-γ, IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p70, IL-13, and TNF-α measured using Mesoscale Discovery Multiplex Assays). This evidence concerns the gene IFNG and major depressive disorder.